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EC2304 Microprocessors and Microcontrollers Notes

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EC2304 Microprocessors and Microcontrollers Question Bank Prepared from previous year questions - 2 marks with answer + 16 marks


Part A ( 2 Marks)


1.What is Microprocessor ?
It is a program controlled semiconductor device (IC}, which fetches,
decode and executes instructions.
2. What are the basic units of a microprocessor ?
The basic units or blocks of a microprocessor are ALU, an array of
registers and control unit.
3.what is Software and Hardware?
The Software is a set of instructions or commands needed for
performing a specific task by a programmable device or a computing
machine.
The Hardware refers to the components or devices used to form
computing machine in which the software can be run  and tested.
Without software the Hardware is an idle machine. 4. What is assembly language?
The language in which the mnemonics (short -hand form of
instructions) are used to write a program is called assembly language.
The manufacturers of microprocessor give the mnemonics.
5. What are machine language and assembly language programs?
The software developed using 1's and 0's are called machine language,
programs. The software developed using mnemonics are called
assembly language programs.
6. What is the drawback in machine language and assembly language,
programs?
 The machine language and assembly language programs are machine
dependent. The programs developed using these languages for a
particular machine cannot be directly run on another machine .
7. Define bit, byte and word.
A digit of the binary number or code is called bit. Also, the bit is the
fundamental storage unit of computer memory.
The 8-bit (8-digit) binary number or code is called byte and 16-bit
binary number or code is called word. (Some microprocessor
manufactures refer the basic data size operated by  the processor as
word). 8. What is a bus?
Bus is a group of conducting lines that carries data, address and control
signals.
9. Why data bus is bi-directional?
The microprocessor has to fetch (read) the data from memory or input
device for processing and after processing, it has  to store (write) the
data to memory or output device. Hence the data bus is bi-directional.
10. Why address bus is unidirectional?
The address is an identification number used by the microprocessor to
identify or access a memory location or I / O device. It is an output
signal from the processor. Hence the address bus is unidirectional.
11. What is the function of microprocessor in a system?
The microprocessor is the master in the system, which controls all the
activity of the system. It issues address and control signals and fetches
the instruction and data from memory. Then it executes the instruction
to take appropriate action.
12. What are the modes in which 8086 can operate?
The 8086 can operate in two modes and they are minimum (or
uniprocessor) mode and maximum ( or multiprocessor) mode. 13. What is the data and address size in 8086?
The 8086 can operate on either 8-bit or 16-bit data. The 8086 uses 20
bit address to access memory and 16-bit address to access 1/0 devices.
14. Explain the function of M/IO  in 8086.
The signal  M/IO is used to differentiate memory address and 1/0
address When the processor is accessing memory locations MI  10 is
asserted high and when it is accessing 1/0 mapped devices it is asserted
low.
15. Write the flags of 8086.
 The 8086 has nine flags and they are
1. Carry Flag (CF) 6. Overflow Flag (OF)
2. Parity Flag (PF) 7. Trace Flag (TF)
3. Auxiliary carry Flag (AF) 8. Interrupt Flag (IF)
4. Zero Flag (ZF) 9. Direction Flag (DF)
5. Sign Flag (SF)
16. What are the interrupts of 8086?
The interrupts of 8085 are INTR and NMI. The INTR is general
maskable interrupt and NMI is non-maskable interrupt. 17. How clock signal is generated in 8086? What is the maximum internal
clock frequency of 8086?
The 8086 does not have on-chip clock generation circuit. Hence the
clock generator chip, 8284 is connected to the CLK  pin of8086. The
clock signal supplied by 8284 is divided by three for internal use. The
maximum internal clock frequency of8086 is 5MHz.
18. Write the special functions carried by the general purpose registers of
8086.
The special functions carried by the registers of 8086 are the following.
Register Special function
1. AX 16-bit Accumulator
2. AL 8-bit Accumulator
3. BX Base Register
4. CX Count Register
5. DX .Data Register
19. What is pipelined architecture?
In pipelined architecture the processor will have number of functional
units and the execution time of functional units are overlapped. Each
functional unit works independently most of the time.
20.  What are the functional units available in 8086 architecture?
The bus interface unit and execution unit are the two functional units
available in 8086 architecture. 21. List the segment registers of  8086.
The segment registers of 8086 are Code segment, Data segment, Stack
segment and Extra segment registers.
22. Define machine cycle.
 Machine cycle is defined as the time required to complete one
operation of accessing memory, I/O, or acknowledging an external
request. This cycle may consist of three to six T-states.
23. Define T-State.
   T-State is defined as one subdivision of the operation performed in
one clock period. These subdivisions are internal states synchronized
with the system clock, and each T-State is precisely equal to one
clock period.
24. List the components of microprocessor (single board microcomputer)
based system
The microprocessor based system consist of microprocessor as CPU,
semiconductor memories like EPROM and RAM, input device, output
device and interfacing devices. 25. Why interfacing is needed for 1/0 devices?
Generally I/O devices are slow devices. Therefore the speed of I/O
devices does not match with the speed of microprocessor. And so an
interface is provided between system bus and I/O devices.
26. What is the difference between CPU bus and system bus?
The CPU bus has multiplexed lines but the system bus has separate
lines for each signal. (The multiplexed CPU lines are demultiplexed by
the CPU interface circuit to form system bus).
27..What does memory-mapping mean?
The memory mapping is the process of interfacing memories to
microprocessor and allocating addresses to each memory locations.
28..What is interrupt 1/0?
If the 1/0 device initiate the data transfer through interrupt then the 1/0
is called interrupt driven 1/0.
29. Why EPROM is mapped at the beginning of memory space in 8085  
      system?
In 8085 microprocessor, after a reset, the program  counter will have
OOOOH address. If the monitor program is stored from this address
then after a reset, it will be executed automatically. The monitor program is a permanent program and stored in EPROM  memory. If
EPROM memory is mapped at the beginning of memory space, i.e., at
OOOOH, then the monitor program will be executed automatically
after a reset.
30. What is the need for system clock and how it is generated in 8085?
The system clock is necessary for synchronizing various internal
operations or devices in the microprocessor and to  synchronize the
microprocessor with other peripherals in the system.
31.What is DMA?
The direct data transfer between I/O device and memory is called
DMA.
32. What is the need for Port?
The I/O devices are generally slow devices and their timing
characteristics do not match with processor timings. Hence the I/O
devices are connected to system bus through the ports.
33.What is a port?
The port is a buffered I/O, which is used to hold the data transmitted    
from the microprocessor to I/O device or vice-versa. 34.Give some examples of port devices used in 8085 microprocessor based
system?
The various INTEL I/O port devices used in 8085 microprocessor
based system are 8212, 8155, 8156, 8255, 8355 and 8755.
35. Write a short note on INTEL 8255?
The INTEL 8255 is a I/O port device consisting of 3 numbers of 8 -bit
parallel I/O ports. The ports can be programmed to function either as a
input port or as a output port in different operating modes. It requires
4 internal addresses and has one logic LOW chip select pin.
36.What is the drawback in memory mapped I/0?
When I/O devices are memory mapped, some of the addresses are
allotted to I/O devices and so the full address space cannot be used for
addressing memory (i.e., physical memory address space will be
reduced). Hence memory mapping is useful only for small systems,
where the memory requirement is less.
37. How DMA is initiated?
When the I/O device needs a DMA transfer, it will send a DMA
request signal to DMA controller. The DMA controller in turn sends a
HOLD request to the processor. When the processor receives a HOLD
request, it will drive its tri-stated pins to high impedance state at the
end of current instruction execution and send an acknowledge signal to
DMA controller. Now the DMA controller will perform DMA transfer. 38. What is processor cycle (Machine cycle)?
The processor cycle or machine cycle is the basic operation performed
by the processor. To execute an instruction, the processor will run one
or more machine cycles in a particular order.
39. What is Instruction cycle?
The sequence of operations that a processor has to  carry out while
executing the instruction is called Instruction cycle. Each instruction
cycle of a processor indium consists of a number of machine cycles.
40. What is fetch and execute cycle?
In general, the instruction cycle of an instruction can be divided into
fetch and execute cycles. The fetch cycle is executed to fetch the
opcode from memory. The execute cycle is executed to decode the
instruction and to perform the work instructed by the instruction.
41.What is Block and Demand transfer mode DMA?
In Block transfer mode, the DMA controller will transfer a block of
data and relieve the bus for processor. After sometime another block
of data is transferred by DMA and so on.
In Demand transfer mode the DMA controller will complete the entire
.data transfer at a stretch and then relieve the bus to processor. 42. What is the need for timing diagram?
The timing diagram provides information regarding the status of
various signals, when a machine cycle is executed. The knowledge of
timing diagram is essential for system designer to  select matched
peripheral devices like memories, latches, ports, etc., to form a
microprocessor system.
43. How many machine cycles constitute one instruction cycle in 8085?
Each instruction of the 8085 processor consists of one to five machine
cycles.
44. Define opcode and operand.
Opcode (Operation code) is the part of an instruction / directive that        
identifies a specific operation.
Operand is a part of an instruction / directive that represents a value
on which the instruction acts.
45. What is opcode fetch cycle?
The opcode fetch cycle is a machine cycle executed to fetch the opcode
of an instruction stored in memory. Every instruction starts with opcode
fetch machine cycle. 46. What operation is performed during first T -state of every machine cycle
in 8085 ?
In 8085, during the first T -state of every machine cycle the low byte
address is latched into an external latch using ALE signal.
47. Why status signals are provided in microprocessor?
The status signals can be used by the system designer to track the
internal operations of the processor. Also, it can be used for memory
expansion (by providing separate memory banks for program & data
and selecting the bank using status signals).
48. How the 8085 processor differentiates a memory  access (read/write)
and 1/0 access (read/write)?
The memory access and 1/0 access is differentiated using 10 I M signal.
The 8085 processor asserts 10 I M low for memory read/write operation
and 10 I M is asserted high for 1/0 read/write operation.
49. When the 8085 processor checks for an interrupt?
In the second T -state of the last machine cycle of every instruction, the
8085 processor checks whether an interrupt request is made or not.
50. What is interrupt acknowledge cycle?
The interrupt acknowledge cycle is a machine cycle executed by 8085
processor to get the address of the interrupt service routine in-order to
service the interrupt device. 51. How the interrupts are affected by system reset?
    Whenever the processor or system is resetted , all the interrupts except
TRAP are disabled. fu order to enable the interrupts, El instruction has
to be executed after a reset.
52. What is Software interrupts?
The Software interrupts are program instructions. These instructions
are inserted at desired locations in a program. While running a
program, if software interrupt instruction is encountered then the
processor executes an interrupt service routine.
53. What is Hardware interrupt?
If an interrupt is initiated in a processor by an appropriate signal at the
interrupt pin, then the interrupt is called Hardware interrupt.
54. What is the difference between Hardware and Software interrupt?
The Software interrupt is initiated by the main program, but the
Hardware interrupt is initiated by an external device.
In 8085, the Software interrupt cannot be disabled  or masked but the
Hardware interrupt except TRAP can be disabled or masked. 55. What is Vectored and Non- Vectored interrupt?
     When an interrupt is accepted, if the processor control branches to a      
specific address defined by the manufacturer then the interrupt is
called vectored interrupt.
      In Non-vectored interrupt there is no specific address for storing the
interrupt service routine. Hence the interrupted device should give the
address of the interrupt service routine.
56. List the Software and Hardware interrupts of 8085?
Software interrupts: RST 0, RSTl, RST 2,
RST 3, RST 4, RST 5,
RST 6 and RST 7.
Hardware interrupts: TRAP, RST 7.5, RST 6.5,
RST 5.5 and INTR.
57. What is TRAP?
The TRAP is non-maskable interrupt of8085. It is not disabled by
processor reset or after reorganization of interrupt.
58. Whether HOLD has higher priority than TRAP or not?
The interrupts including mAP are recognized only if the HOLD is not
valid, hence TRAP has lower priority than HOLD. 59. What is masking and why it is required?
Masking is preventing the interrupt from disturbing the current
program execution. When the processor is performing an
important job (process) and if the process should not be
interrupted then all the interrupts should be masked or disabled.
In processor with multiple 'interrupts, the lower priority interrupt
can be masked so as to prevent it from interrupting, the execution
of interrupt service routine of higher priority interrupt.
60. When the 8085 processor accept hardware interrupt?
The processor keeps on checking the interrupt pins at the second T
-state of last Machine cycle of every instruction. If the processor
finds a valid interrupt signal and if the interrupt is unmasked and
enabled then the processor accepts the interrupt. The acceptance
of the interrupt is acknowledged by sending an OOA signal to the
interrupted device.
61. When the 8085 processor will disable the interrupt system?
The interrupts of 8085 except TRAP are disabled after anyone of the
following operations
1. Executing El instruction.
2. System or processor reset.
3. After reorganization (acceptance) of an interrupt. 62. What is the function performed by Dl instruction?
The function of Dl instruction is to enable the disabled interrupt system.
63. What is the function performed by El instruction?
The El instruction can be used to enable the interrupts after disabling.
64. How the vector address is generated for the INTR interrupt of 8085?
For the interrupt INTR, the interrupting device has to place either RST
opcode or CALL opcode followed by l6-bit address. I~RST opcode is
placed then the corresponding vector address is generated by the
processor. In case of CALL opcode the given l6-bit address will be the
vector address.
65. How clock signals are generated in 8085 and what is the frequency of
the internal clock?
The 8085 has the clock generation circuit on the chip but an external
quartz crystal or L C circuit or RC circuit should be connected at the
pins XI and X2. The maximum internal clock frequency of 8085A is
3.03 MHz. 66. What happens to the 8085 processor when it is resetted?
When the 8085 processor is resetted it execute the first instruction at the
OOOOH location. The 8085 resets (clears) instruction register, interrupt
mask bits and other registers.
67. What are the operations performed by ALU of 8085?
The operations performed by ALU of 8085 are Addition, Subtraction,
Logical AND, OR, Exclusive OR, Compare Complement,  Increment,
Decrement and Left I Right shift
68. What is a flag?
Flag is a flip flop used to store the information about the status of the
processor and the status of the instruction executed most recently.
69. List the flags of 8085
There are five flags in 8085. They are sign flag, zero flag, Auxiliary
carry flag, parity flag and carry flag.
70. What is the Hardware interrupts of 8085?
The hardware interrupts in 8085 are TRAP, RST 7.5, RST 6.5 and
RST 5,5. 41.  71.Which interrupt has highest priority in 8085? What is the priority of
other interrupts?
The TRAP has the highest priority, followed by RST  7.5, RST 6.5,
RST 5.5 and INTR.
72 What is an ALE?
The ALE (Address Latch Enable) is a signal used to  demultiplex the
address and data lines, using an external latch. It is used to enable the
external latch.
73. Explain the function of IO/M in 8085.
The IO/M is used to differentiate memory access and I/O access. For IN
and OUT instruction it is high. For memory reference instructions it is
low.
74. Where is the READY signal used?
READY is an input signal to the processor, used by the memory or I/O
devices to get extra time for data transfer or to introduce wait states in
the bus cycles.
75. What is HOLD and HLDA and how it is used?
Hold and hold acknowledge signals are used for the  Direct Memory
Access (DMA) type of data transfer. The DMA controller place a high
on HOLD pin in order to take control of the system bus. The HOLD
request is acknowledged by the 8085 by driving all its tristated pins to
high impedance state and asserting HLDA signal high. 76.What is Polling?
Polling is a scheme or an algorithm to identify the devices interrupting
the processor. Polling is employed when multiple devices interrupt the
processor through one interrupt pin of the processor.
77. What are the different types of Polling?
The polling can be classified into software and hardware polling. In
software polling the entire polling process is govern by a prograrn.1n
hardware polling, the hardware takes care of checking the status of
interrupting devices and allowing one by one to the processor.
78.What is the need for interrupt controller?
The interrupt controller is employed to expand the interrupt inputs. It
can handle the interrupt request from various devices and allow one by
one to the processor.
79. List some of the features of INTEL 8259 (Programmable Interrupt
Controller)
1. It manage eight interrupt request
2. The interrupt vector addresses are programmable.
3. The priorities of interrupts are programmable.
4. The interrupt can be masked or unmasked individually. 80. What is a programmable peripheral device ?
If the functions performed by a peripheral device can be altered or
changed by a program instruction then the peripheral device is called
programmable device. Usually the programmable devices will have control
registers. The device can be programmed by sending  control word in the
prescribed format to the control register.
81. What is synchronous data transfer scheme?
For synchronous data transfer scheme, the processor does not check the
readiness of the device after a command have been issued for
read/write operation. fu this scheme the processor  will request the
device to get ready and then read/W1.ite to the device immediately
after the request. In some synchronous schemes a small delay is
allowed after the request.
82. What is asynchronous data transfer scheme?
In asynchronous data transfer scheme, first the processor sends a
request to the device for read/write operation. Then the processor
keeps on polling the status of the device. Once the device is ready, the
processor execute a data transfer instruction to complete the process.
83. What are the operating modes of 8212?
The 8212 can be hardwired to work either as a latch or tri-state buffer.
If mode (MD) pin is tied HIGH then it will work as a latch and so it can be used as output port. If mode (MD) pin is tied LOW then it
work as tri- state buffer and so it can be used as input port.
84. Explain the working of a handshake output port
In handshake output operation, the processor will load a data to port.
When the port receives the data, it will inform the output device to
collect the data. Once the output device accepts the data, the port will
inform the processor that it is empty. Now the processor can load
another data to port and the above process is repeated.
85.What are the internal devices of  8255 ?
The internal devices of 8255 are port-A, port-B and port-C. The ports
can be programmed for either input or output function in different
operating modes.
86. What is baud rate?
The baud rate is the rate at which the serial data are transmitted. Baud
rate is defined as l /(The time for a bit cell). In some systems one bit
cell has one data bit, then the baud rate and bits/sec are same.
87. What is USART?
The device which can be programmed to perform Synchronous or
Asynchronous serial communication is called USART (Universal
Synchronous Asynchronous Receiver Transmitter). The INTEL 8251A is an example of USART.
88. What are the functions performed by INTEL 8251A?
The INTEL 825lA is used for converting parallel data to serial or vice
versa. The data transmission or reception can be either asynchronously
or synchronously. The 8251A can be used to interface MODEM and
establish serial communication through MODEM over telephone lines.
89. What is an Interrupt?
Interrupt is a signal send by an external device to the processor so as to
request the processor to perform a particular task or work.
90. What are the control words of 8251A and what are its functions ?
The control words of 8251A are Mode word and Command word.
The mode word informs 8251 about the baud rate, character length,
parity and stop bits. The command word can be send to enable the
data transmission and  reception.
91. What are the information that can be obtained from the status word of
8251 ?
The status word can be read by the CPU to check the readiness of the
transmitter or receiver and to check the character synchronization in
synchronous reception. It also provides information regarding various
errors in the data received. The various error conditions that can be checked from the status word are parity error, overrun error and
framing error.
92. Give some examples of input devices to microprocessor-based system.
The input devices used in the microprocessor-based  system are
Keyboards, DIP switches, ADC, Floppy disc, etc.
93. What are the tasks involved in keyboard interface?
The task involved in keyboard interfacing are sensing a key actuation,
Debouncing the key and Generating key codes (Decoding the key).
These task are performed software if the keyboard is interfaced
through ports and they are performed by hardware if the keyboard is
interfaced through 8279.
94. How a keyboard matrix is formed in keyboard interface using 8279?
The return lines, RLo to RL7 of 8279 are used to form the columns of
keyboard matrix. In decoded scan the scan lines SLo to SL3 of 8279
are used to form the rows of keyboard matrix. In encoded scan mode,
the output lines of external decoder are used as rows of keyboard
matrix.
95. What is scanning in keyboard and what is scan time?
The process of sending a zero to each row of a keyboard matrix and
reading the columns for key actuation is called scanning. The scan time is the time taken by the processor to scan all the  rows one by one
starting from first row and coming back to the first row again.
96. What is scanning in display and what is the scan time?
In display devices, the process of sending display codes to 7 -segment
LEDs to display the LEDs one by one is called scanning ( or
multiplexed display). The scan time is the time taken to display all the
7-segment LEDs one by one, starting from first LED and coming back
to the first LED again.
97. What are the internal devices of a typical DAC?
The internal devices of a DAC are R/2R resistive network, an internal
latch and current to voltage converting amplifier.
98. What is settling or conversion time in DAC?
The time taken by the DAC to convert a given digital data to
corresponding analog signal is called conversion time.
99. What are the different types of ADC?
The different types of ADC are successive approximation ADC,
counter type ADC flash type ADC, integrator converters and voltageto-frequency converters. 100. Define stack
Stack is a sequence of RAM memory locations defined by the
programmer.
101. What is program counter? How is it useful in program execution?
The program counter keeps track of program execution. To execute a
program the starting address of the program is loaded in program
counter. The PC sends out an address to fetch a byte of instruction from
memory and increments its content automatically.
102. How the microprocessor is synchronized with peripherals?
The timing and control unit synchronizes all the microprocessor
operations with clock and generates control signals necessary for
communication between the microprocessor and peripherals.
103. What is a minimum system and how it is formed in 8085?
A minimum system is one which is formed using minimum number of
IC chips, The 8085 based minimum system is formed using 8155,8355
and 8755.
104. What is mean by microcontroller
    A device which contains the microprocessor with integrated
peripherals like memory, serial ports, parallel ports, timer/counter, interrupt
controller, data acquisition interfaces like ADC,DAC is called
microcontroller. 105.List the features of 8051 microcontroller?
   The features are
      *single_supply +5 volt operation using HMOS technology.
   *4096 bytes program memory on chip(not on 8031)
  *128 data memory on chip.
  *Four register banks.
  *Two multiple mode,16-bit timer/counter.
  *Extensive boolean processing capabilities.
                     *64 KB external RAM size
                     *32 bidirectional individually addressible I/O lines.
                     *8 bit CPU optimized for control applications.
106.Explain the operating mode0 of  8051 serial ports?
  In this mode serial enters &exits through RXD, TXD outputs
the shift clock.8 bits are transmitted/received:8 data bits(LSB first).The baud
rate is fixed at 1/12 the oscillator frequency.
107 Explain the operating mode2 of 8051 serial ports?
  In this mode 11 bits are transmitted(through TXD)or received
(through RXD):a start bit(0), 8 data bits(LSB first),a programmable 9th  data
bit ,& a stop bit(1).ON transmit the 9
th
 data bit (TB* in SCON)can be
assigned the value of 0 or 1.Or for eg:, the parity bit(P, in the PSW)could be
moved into TB8.On receive the 9
th
 data bit go  in to the RB8 in Special Function Register SCON, while the stop bit is ignored. The baud rate is
programmable to either 1/32or1/64 the oscillator frequency.
108. Explain the mode3 of 8051 serial ports?
  In this mode,11 bits are transmitted(through TXD)or
received(through RXD):a start bit(0), 8 data bits(LSB first),a programmable
9th  data bit ,& a stop bit(1).In fact ,Mode3 is the same as Mode2 in all
respects except the baud rate. The baud rate in Mode3 is variable.
                    In all the four modes, transmission is initiated by any instruction
that uses SBUF as a destination register. Reception is initiated in Mode0 by
the condition RI=0&REN=1.Reception is initiated in  other modes by the
incoming start bit if REN=1.
 109.Explain the interrupts of 8051 microcontroller?
   The interrupts  are:
                                                                          Vector address
• External interrupt 0      :   IE0        :       0003H
• Timer interrupt 0          :  TF0        :       000BH
• External interrupt 1      :   IE1        :       0013H
• Timer Interrupt 1          :  TF1        :       001BH
• Serial Interrupt
                   Receive interrupt : RI       :        0023H
                   Transmit interrupt: TI       :        0023H 110.Write A program to perfom multiplication of 2 nos using 8051?
                    MOV A,#data 1
                    MOV B,#data 2
                    MUL AB
                    MOV DPTR,#5000
                    MOV @DPTR,A(lower value)
                    INC DPTR
                    MOV A,B
                    MOVX @ DPTR,A
111.Write a program to mask the 0
th
 &7
th
 bit using 8051?
    MOV A,#data
                               ANL A,#81
                               MOV DPTR,#4500
   MOVX @DPTR,A
   LOOP  SJMP  LOOP
112.List the addressing modes of 8051?
• Direct addressing
• Register addressing
• Register indirect addressing.
• Implicit addressing
• Immediate addressing
• Index addressing
• Bit addressing   113.Write about CALL statement in 8051?
                       There are two subroutine CALL instructions. They are
                            *LCALL(Long CALL)
                            *ACALL(Absolute CALL)
             Each increments the PC to the 1
st
 byte of the instruction & pushes them
in to the stack.
 
114.Write about the jump statement?
                             There are three forms of jump. They are
LJMP(Long jump)-address 16
AJMP(Absolute Jump)-address 11
SJMP(Short Jump)-relative address
115.Write program to load accumulator ,DPH,&DPL using 8051?
                          MOV A,#30
                       MOV DPH,A
                       MOV DPL,A
116.Write a program to find the 2’s complement using 8051?
                     MOV A,R0
                     CPL A
                     INC A
117.Write a program  to add 2 8-bit numbers using 8051?
                         MOV A,#30H
                         ADD A,#50H 118.Write a program to swap two numbers using 8051?
                      MOV A, #data
                      SWAP A
119.Write a program to subtract 2 8-bit numbers &exchange the digits using  
       8051?
                       MOV A,#9F
                          MOV  R0,#40
                          SUBB A,R0
                          SWAP A
 120.Write a program to subtract the contents of R1 of Bank 0from the contents
         of R0 of Bank 2 using 8051?
                        MOV  PSW,#10
                        MOV A,R0
                        MOV PSW,#00
                        SUBB A,R1







Part B 




1. Draw & explain the architecture of 8085 microprocessor
• Block Diagram
• Registers Available
• Function Of Accumulator
• Explanation about all blocks in the block diagram
       2.  Draw the Pin Diagram of 8085 and explain the function of various signals.
• Pin Diagram
• Explanation about all signals
3. Explain the instruction classification & instruction sets
• Data Transfer Instructions
• Arithmetic Instructions
• Logical Instructions
• Branch Instructions
• Machine Control Instructions
    4. Write a program to sort the numbers in ascending and descending order.
• Program
• Result Verification
   5.Draw the timing diagram of the following Instructions
• PUSH
• IN Port A
• STA 5000
• MVI A, 08
• Explain the machine cycles needed for every Instructions and
draw the timing diagram
6. Explain the 8085 based microcomputer system
      7. With neat sketch explain the functions of 8255 PPI.
• Block Diagram
• Explanation about all the ports available.
• Explanation about the modes of transfer
• Explain the control Word Register
     8. With neat sketch explain the functions of 8251.
• Block Diagram
• Types of data transfer
• Explanation about all the blocks. • Explain the control Word Register, Status Register
    9.  With neat sketch explain the function of DMA contoller.
• Block Diagram
• Explanation about all blocks in the block diagram
    10.With neat sketch explain the function of Programmable Interrupt Controller.
• Block Diagram
• Explanation about all blocks in the block diagram
     11.With neat sketch explain the function of Keyboard and display controller.
• Block Diagram
• Types of Display Available
• Types of keys available
• Explanation about all blocks in the block diagram
    12. With neat sketch explain the function of A/D converter.
• Fundamental steps
• Figure
• Explain the functions.
    13. With neat sketch explain the function of D/A converter.
• Fundamental steps
• Figure
• Explain the functions.
    14.With neat sketch explain the architecture of 8051 microcontroller.
• Block Diagram
• Explanation about all blocks in the block diagram
    15. Draw the Pin Diagram of 8051 and explain the function of various
signals.
• Pin Diagram
• Explanation about all signals
16. List the various Instruction available in 8051 microcontroller.
• Data Transfer Instructions
• Arithmetic Instructions
• Logical Instructions
• Boolean variable Manipulation Instructions
• Program and Machine Control Instructions

by Vinoth · 0

EC2305 Transmission Lines and Wave guides Question Bank Prepared from previous year questions - 2 marks with answer + 16 marks


DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING 
                    SUBJECT CODE: EC 2305 
SUBJECT: TRANSMISSION LINES AND WAVEGUIDES 
(FOR FIFTH SEMESTER ECE)



TWO MARKS QUESTIONS

UNIT I-TRANSMISSION LINE THEORY 

1.Define the line parameters?
            The parameters of a transmission line are:
                          Resistance (R)
                          Inductance (L)
                          Capacitance (C)
                          Conductance (G)
            Resistance (R) is defined  as the loop resistance per unit length of the wire. Its                                      
unit is ohm/Km
            Inductance (L) is defined as the loop inductance per unit length of the wire. Its
unit is Henry/Km
            Capacitance (C) is defined as the loop capacitance per unit length of the wire. Its
unit is Farad/Km
            Conductance (G) is defined as the loop conductance per unit length of the wire.
Its unit is mho/Km

2. What are the secondary constants of a line? Why the line parameters are called
distributed elements?
                 
              The secondary constants of a line are:
                                 Characteristic Impedance
                                  Propagation Constant
             Since the line constants R, L, C, G are distributed through the entire length of the
line, they are called as distributed elements. They are also called as primary constants.    
           
3.Define Characteristic impedance
              Characteristic impedance is the impedance measured at the sending end of the
line. It is given by Z0 =   Z/Y,where
                              Z = R + jωL   is the series impedance
                              Y = G + jωC  is the shunt admittance          4. Define Propagation constant
               Propagation constant is defined as the natural logarithm of the ratio of the
sending end current or voltage to the receiving end current or voltage of the line. It gives
the manner in the wave is propagated along a line and specifies the variation of voltage
and current in the line as a function of distance. Propagation constant is a complex
quantity and is expressed as
                                          γ  = α + j β
               The real part is called the attenuation constant α whereas the imaginary part of
propagation constant is called the phase constant β
5.What is a finite line? Write down the significance of this line?
                  A finite line is a line having a finite length on the line. It is a line, which is
terminated, in its characteristic impedance (ZR=Z0), so the input impedance of the finite
line is equal to the characteristic impedance (Zs=Z0).
6.What is an infinite line?
                  An infinite line is a line in which the length of the transmission line is infinite.
A finite line, which is terminated in its characteristic impedance, is termed as infinite
line. So for an infinite line, the input impedance is equivalent to the characteristic
impedance.
7.What is wavelength of a line?
                  The distance the wave travels along the line while the phase angle is changing
through 2Π radians is called a wavelength.
8.What are the types of line distortions?
                   The distortions occurring in the transmission line are called waveform
distortion or line distortion. Waveform distortion is of two types:
                         a) Frequency distortion
                         b) Phase or Delay Distortion.
9.How frequency distortion occurs in a line?
                   When a signal having many frequency components are transmitted along the
line, all the frequencies will not have equal attenuation and hence the received end
waveform will not be identical with the input waveform at the sending end because each
frequency is having different attenuation. This type of distortion is called frequency
distortion.
10.How to avoid the frequency distortion that occurs in the line?
                 In order to reduce frequency distortion occurring in the line,
                        a) The attenuation constant α   should be made independent of frequency.            
b) By using equalizers at the line terminals which minimize the  frequency
distortion. Equalisers are networks whose frequency and phase
characteristics are adjusted to be inverse to those of the lines, which result in a uniform frequency response over the desired frequency band, and
hence the attenuation is equal for all the frequencies.
11.What is delay distortion?    
                 When a signal having many frequency components are transmitted along the
line, all the frequencies will not have same time of transmission, some frequencies being
delayed more than others. So the received end waveform will not be identical with the
input waveform at the sending end because some frequency components will be delayed
more than those of other frequencies. This type of distortion is called phase or delay
distortion.
12. How to avoid the frequency distortion that occurs in the line?
               In order to reduce frequency distortion occurring in the line,
a) The phase constant β should be made dependent of frequency.    
b) The velocity of propagation is independent of frequency.        
c) By using equalizers at the line terminals which minimize the frequency
distortion. Equalizers are networks whose frequency and phase
characteristics are adjusted to be inverse to those of the lines, which
result in a uniform frequency response over the desired frequency
band, and hence the phase is equal for all the frequencies.
13.What is a distortion less line? What is the condition for a distortion less line?
                  A line, which has neither frequency distortion nor phase distortion is called a
distortion less line. The condition for a distortion less line is RC=LG. Also,
                        a) The attenuation constant α   should be made independent of frequency.                
                        b) The phase constant β should be made dependent of frequency.    
d) The velocity of propagation is independent of frequency.
14.What is the drawback of using ordinary telephone cables?
                  In ordinary telephone cables, the wires are insulated with paper and twisted in
pairs, therefore there will not be flux linkage between the wires, which results in
negligible inductance, and conductance. If this is the case, the there occurs frequency and
phase distortion in the line.
15.How the telephone line can be made a distortion less line?
                  For the telephone cable to be distortion less line, the inductance value should
be increased by placing lumped inductors along the line.
16.What is Loading?
                  Loading is the process of increasing the inductance value by placing lumped
inductors at specific intervals along the line, which avoids the distortion     17.What are the types of loading?
                     a) Continuous loading
                     b) Patch loading
                     c) Lumped loading  
   
18.What is continuous loading?
                  Continuous loading is the process of increasing the inductance value by
placing a iron core or a magnetic tape over the conductor of the line.  
 
19.What is patch loading?
                  It is the process of using sections of continuously loaded cables separated by
sections of unloaded cables which increases the inductance value
20.What is lumped loading?
                Lumped loading is the process of increasing the inductance value by placing
lumped inductors at specific intervals along the line, which avoids the distortion    
21.Define reflection coefficient
               Reflection Coefficient can be defined as the ratio of the reflected voltage to the
incident voltage at the receiving end of the line
               Reflection Coefficient K=Reflected Voltage at load /Incident voltage at the load
                                                K=Vr/Vi
  22. Define reflection loss
                Reflection loss is defined as the number of nepers or decibels by  which the              
current in the load under image matched conditions would exceed the current actually
flowing in the load
23.What is Impedance matching?
                If the load impedance is not equal to the source impedance, then all the power
that are transmitted from the source will not reach the load end and hence some power is
wasted. This is called impedance mismatch condition. So for proper maximum power
transfer, the impedances in the sending and receiving end are matched. This is called
impedance matching.
24. Define the term insertion loss
                 The insertion loss of a line or network is defined as the number of nepers or
decibels by which the current in the load is changed by the insertion .      
Insertion loss=Current flowing in the load without insertion of the
network/Current flowing in the load with insertion of the network  
    25.When reflection occurs in a line?
                  Reflection occurs because of the following cases:
                       1) when the load end is open circuited
                       2) when the load end is short-circuited
                       3) when the line is not terminated in its characteristic impedance
        When the line is either open or short circuited, then there is not resistance at the
receiving end to absorb all the power transmitted from the source end. Hence all the
power incident on the load gets completely reflected back to the source causing
reflections in the line. When the line is terminated in its characteristic impedance, the
load will absorb some power and some will be reflected back thus producing reflections.
26.What are the conditions for a perfect line? What is a smooth line?
                      For a perfect line, the resistance and the leakage conductance  value were
neglected. The conditions for a perfect line are R=G=0.
                      A smooth line is one in which the load is terminated by its characteristic
impedance and no reflections occur in such a line. It is also called as flat line.



UNIT II-RADIO FREQUENCY LINE



27. State the assumptions for the analysis of the performance of the radio frequency
line.
1.Due to the skin effect ,the currents are assumed to flow on the  surface of  the
conductor. The  internal inductance is zero.
2.The resistance R increases with   √ f  while inductance  L increases with  f .
  Hence ωL>>R.
  3.The leakage conductance G  is zero
28.State the expressions for inductance L of a open wire  line and coaxial line.
For open wire line ,
                                               
                                         L=9.21*10
-7
(µ/µr +4ln d/a)=10
-7
(µr+9.21log d/a) H/m
           For coaxial line,
                                     L = 4.60*10
-7
[log b/a]H/m
29.State the expressions for the capacitance  of a open wire line
For open wire line ,
                        C=(12.07)/(ln d/a)µµf/m
30.What is dissipationless line?
A line for which the effect  of resistance R is completely  neglected is called
dissipationless line . 31.What is the nature and value of  Z0 for the dissipation less line?
  For the dissipation less  line, the  Z0 is purley resistive and given  by,
                                                             Z0=R0 = √  L/c
32.State the values of  ααα  and βββ for the dissipation less  line.
 Answer:
              α=0 and   β=ω √LC
33.What are nodes and antinodes on a line?
The points along the line where magnitude of  voltage or current is zero  are
called nodes  while the the points along the lines where magnitude of  voltage or current
first maximum  are called antinodes  or  loops.
34.What is standing  wave ratio?
The ratio of the maximum to minimum  magnitudes  of voltage or current on a
line having  standing  waves called standing  waves ratio.
                                                 Emax        Imin
                                    S =                  =    
                Emin         Imin
35.What is the range of values of standing  wave ratio?
The range of  values of standing wave ratio is theoretically 1 to  infinity.
36.State the relation between standing wave ratio and reflection coefficient.
Ans:                          S =  1+K
                                             
                                            1-K
37.What are standing waves?
If the transmission is not terminated in its characteristic impedance ,then there
will be two waves traveling along the line which gives rise to standing waves having
fixed maxima and fixed minima.
38.What is called  standing  wave ratio?
The ratio of the maximum to minimum magnitudes of current or voltage on a line
having standing wave is called the standing-wave ratio S. That is,
 
  S=  E max        = I max      
      Emin              I min
 
               
39.State  the relation between standing were ratio S and reflection co-efficient k.
 The relation between standing wave ratio S and reflection co-efficient k is,
             1+  k
  S  =
1- k
S-1
Also    k     =
  S+1
  40. How will you make standing wave measurements on coaxial lines?
For coaxial lines it is necessary to use a length of line in which a longitudinal
slot, one half wavelength or more long has been cut.  A wire probe is inserted into
the air dielectric of the line as a pickup device, a vacuum tube voltmeter or other
detector being connected between probe and sheath as an indicator.  If the meter
provides linear indications, S is readily determined.  If the indicator is non linear,
corrections must be applied to the readings obtained.
41.Give the input impedance of a dissipationless line.
The input impedance of a dissipationless line is given by,
 
 Z
s
 =  Es
  = R0  1+  k < φφφ -2βββs
                     I s
           1-  k  <φφφ -2βββs
42.Give the maximum  and minimum input impedance of the dissipationless line.
Maximum input impedance,
 R max = R0  1+   k
                               1-   k
 
= SRo    
Minimum input impedance,
R min = Ro  1+   k  
                              1-   k
 
=  Ro
                                 S
      43.Give the input impedance of open and short circuited lines.
  The input impedance of open aned short circuited lines are given by,   Zsc = jRo tan
2 πs
                                                                                           
λ
      44.Why the point of voltage minimum is measured rather than voltage  
maximum?
The point of a voltage minimum is measured rather than a voltage
maximum because it is usually possible to determine the exact point of
minimum voltage with greater accuracy.
45. What is the use of eighth wave line?
              An eighth wave line is used  to transform any resistance to an impendence with a
magnitude equal to Roof the  line  or to obtain a magnitude match between a resistance of
any value  and a source of Ro internal resistance.
46. Give the input impendence of eighth wave line terminated in a pure resistance
Rr.
            The input impendence of eighth wave line terminated in a pure resistance  Rr. Is
given by
                     Zs = (ZR+jRo/Ro+jZR)
         From the above equation it is seen that
                      Zs = Ro.
47. Why is a quarter wave line called as impendence inverter?
              A quater wave line may be considered as an impendence inverter because it can
transform a low impendence in to ahigh impendence and vice versa.
48. What is the application  of the quarter wave matching section ?
         An important  application  of the quarter wave matching sectionis  to a couple a
transmission line  to a resistive load such as an antenna .The quarter –wave matching
section then must be designed to have a characteristic impendence Ro so chosen that the
antenna resistance Ra is transformed to a value equal to the characteristic impendence Ra
of the transmission line.The characteristic impendence  Ro of the matching  section  
then should be
                         Ro’ = √ Ra Ro
49. What do you mean by copper insulators?
            An application of the short circuited quarter wave  line  is an insulator to support
an open wire line  or the center conductor of a coaxial line .This application makes se of
the fact that the input impendence of a quarter –wave shorted line is very high ,Such lines
are sometimes  referred to as copper insulators.
50. Bring out the significance of a  half wavelength line.                            A half wavelength line may be considered as a one- to – one
transformer. It has its greatest utility in connecting load to a source in cases where the
load source cannot be made adjacent.
51. Give some of the impendence –matching devices.
           The quarter – wave line or transformer and the tapered line are  some of the
impendence –matching devices.
52. Explain   impendence matching using stub.
          In the method of impendence matching using stub ,an open or closed stub line of
suitable length is used as a reactance  shunted across the transmission line at a designated
distance from the load ,to tune  the length of the line and the load to resonance with an
antiresonant resistance equal to Ro.
53.Give reasons for preferring  a short- circuited  stub when compared to an open –
circuited stub.
                        A short circuited stub is preferred to an open circuited stub because of
greater ease in constructions and because of the inability to maintain high enough
insulation resistance at the open –circuit point to ensure that the stub is really open-
circuited .A shorted stub also has a lower loss of energy due to radiation ,since the short –
circuit can be definitely established with a large metal plate ,effectively stopping all field
propagation.
54.What are the two independent measurements that must be made to find the
location and length of the stub.
 
                    The standing  wave ratio  S and the position of a voltage minimum are the
independent  measurements that must be made to find the location and length of the stub.
55.Give the formula to calculate the distance of the point from the load at which the
stub is to be connected.
                    The formula to calculate the distance of the point from the load at which the
stub is to be connected is,
                         
                            S1 =  (φ +π-cos
-1
|K|)/(2β)
56. Give the formula to calculate the distance d from the voltage minimum to the
point  stub be connection.
             
 The formula to calculate the distance d from the voltage minimum to the point  of
stub be connection is,
  d= cos
-1
|K| / (2β)
                   
57.  Give the formula to calculate the length of the short circuited stub.                      
                 The formula to calculate the length of the short circuited stub is,
   L=λ/2Π tan
-1
(√s/(s-1))
This is the length of the short – circuited stub to be placed d meters
towards the load from a point at which a voltage minimum existed before
attachment of the stub.
58. What is the input impendence equation of a dissipation less line ?
                   The input impendence equation of a dissipation less line  is given by
   (Zs/Ro)=(1+|K|(Ф-2βs)/ (1-|K|(Ф-2βs)
59.Give the equation for the  radius of a circle diagram.
             
           The equation for the  radius of a circle diagram is
                           
                          R=(S
2
-1)/2S    and
                           
                           C = (S
2
+1)/2S
Where C is the shift of the center of the circle on the positive  Ra axis.
60.What is the use of a circle diagram?
       The circle diagram may be used to find the input impendence of a line mof any
chosen length.
             
61. How is the circle diagram useful to find the input impendence of short and open
circuited lines?
            An open circuited line has s = α ,the correspondent circle appearing as the vertical
axis .The input impendence is then pure reactance , with the value for various electrical
lengths determined by the intersections of the corresponding βs circles with the vertical
axis.
          A short circuited line may be solved by determining its amittance .The S circle is
again the vertical axis, and susceptance values may be read off at appropriate intersection
of the  βs circles with the vertical axis.
62. List the applications of the smith chart.
     The applications of the smith chart are,
(i) It is used to find the input impendence and input admittance of the line.
(ii) The smith chart may also be used for lossy lines and the locus of points on a
line then follows a spiral path towards the chart center, due to attenuation. (iii) In single stub matching    
63. What are the difficulties in single stub matching?
  The difficulties of the smith chart are
(i) Single stub impedance matching requires the stub to be located
at a definite point on the line. This requirement frequently calls
for placement of the stub at an undesirable place from a
mechanical view point.
(ii) For a coaxial line, it is not possible to determine the location of
a voltage minimum without a slotted line section, so that
placement of a stub at the exact required point is difficult.
(iii) In the case of the single stub it was mentioned that two
adjustments were required ,these being location and length of
the stub.
64. What is double stub matching?
 Another possible method of impedance matching is to use two stubs in which the
locations of the stub are arbitrary,the two stub lengths furnishing the required
adjustments.The spacing is frequently  made λ/4.This is called double stub matching.
65. Give reason for an open line not frequently employed for impedance matching.
 An open line is rarely used for impedance matching because of radiation losses
from the open end,and capacitance effects and the difficulty of a smooth adjustment of
length.
66. State the use of half wave line .
           The expression for the input impendence of the line is given by
                                     Zs  =  Zr
Thus the line repeats is terminating impedance .Hence it is operated as one to one
transformer .Its application  is to connect load to a source where they can not be made
adjacent.
67. Why Double stub matching is preferred over single stub matching.
   Double stub matching is preferred over single stub due to following
disadvantages of single stub.
1. Single stub matching  is useful for a fixed frequency . So as frequency changes
the location of single stub will have to be changed.
2. The single stub matching system  is based on the measurement of voltage
minimum .Hence for coxial line it is very difficult to get such voltage
minimum, without using slotted line section.


UNIT III-GUIDED WAVES


68. What are guided waves? Give examples
                         The electromagnetic waves that are guided along or over conducting  or                                          
dielectric surface are called guided waves.
             Examples: Parallel wire, transmission lines
69. What is TE wave or H wave?
                           Transverse electric (TE) wave is a wave in which the electric field
strength E is entirely transverse. It has a magnetic field strength Hz in the direction of
propagation and no component of electric field Ez in the same direction
70. What is TH wave or E wave?
                           Transverse magnetic (TM) wave is a wave in which the magnetic field
strength H is entirely transverse. It has a electric field strength Ez in the direction of
propagation and no component of magnetic field Hz in the same direction
71. What is a TEM wave or principal wave?
                              TEM wave is a special type of TM wave in which an electric field E
along the direction of propagation is also zero. The TEM waves are waves in which both
electric and magnetic fields are transverse entirely but have no components of Ez and Hz
.it is also referred to as the principal wave.
72. What is a dominant mode?
                     The modes that have the lowest cut off frequency is called the dominant
mode.
73. Give the dominant mode for TE and TM waves
                       Dominant mode: TE10 and TM10
                         
74. What is cut off frequency?
                       The frequency at which the wave motion ceases is called cut-off frequency
of the waveguide.
75. What is cut-off wavelength?
                       It is the wavelength below which there is wave propagation and above
which there is no wave propagation.
76. Write down the expression for cut off frequency when the wave is propagated in
between two parallel plates.
                          The cut-off frequency, fc = m/ (2a (µΕ)
1/2
)
77. Mention the characteristics of TEM waves.
              a) It is a special type of TM wave
              b) It doesn’t have either e or H component
              c) Its velocity is independent of frequency
              d) Its cut-off frequency is zero. 78. Define attenuation factor
               Attenuation factor =   (Power lost/ unit length)/(2 x power transmitted)        
79. Give the relation between the attenuation factor for TE waves and TM waves
                             αTE    =     αTM  (fc/f)
2
80. Define wave impedance
                      Wave impedance is defined as the ratio of electric to magnetic field strength
                 
Zxy
= Ex/ Hy     in the positive direction
                 
Zxy
= -Ex/ Hy     in the negative direction
81. What is a parallel plate wave guide?
                 Parallel plate wave guide consists of two conducting sheets separated by a
dielectric material.
                       
                         
82.Why are rectangular wave-guides preferred over circular wave-guides?
              Rectangular wave-guides preferred over circular wave guides because of the
following reasons.
a) Rectangular wave guide is smaller in size than a circular wave guide of the
same operating frequency
b) It does not maintain its polarization through the circular wave guide
c) The frequency difference between the lowest frequency on dominant
mode and the next mode of a rectangular wave-guide is bigger than in a
circular wave guide.
83.Mention the applications of wave guides
              The wave guides are employed for transmission of energy at very high
frequencies where the attenuation caused by wave guide is smaller.
              Waveguides are used in microwave transmission.Circular waveguides are used
as attenuators and phase shifters


UNIT IV-RECTANGULAR WAVEGUIDES


84.Why is circular or rectangular form used as waveguide?
              Waveguides usually take the form of rectangular or circular cylinders because of
its simpler forms in use and less expensive to manufacture.
85. What is an evanescent mode?
          When the operating frequency is lower than the cut-off frequency, the propagation
constant becomes real i.e., γ = α . The wave cannot be propagated. This non- propagating
mode is known as evanescent mode.
87.What is the dominant mode for the TE waves in the rectangular waveguide?
               The lowest mode for TE wave is TE10 (m=1 , n=0) 88. What is the dominant mode for the TM waves in the rectangular waveguide?
               The lowest mode for TM wave is TM11(m=1 , n=1)
89. What is the dominant mode for the rectangular waveguide?
              The lowest mode for TE wave is TE10 (m=1 , n=0) whereas the lowest mode for
TM wave is TM11(m=1 , n=1). The TE10 wave have the lowest cut off frequency
compared to the TM11 mode. Hence the TE10 (m=1 , n=0) is the dominant mode of a
rectangular waveguide.Because the TE10 mode has the lowest attenuation of all modes in
a rectangular waveguide and its electric field is definitely polarized in one direction
everywhere.
10.Which are the non-zero field components for the for the TE10 mode in a rectangular
waveguide?
                      Hx, Hz and Ey.
90. Which are the non-zero field components for the for the TM11 mode in a
rectangular waveguide?
                      Hx, Hy  ,Ey.
 and Ez.
91. Define characteristic impedance in a waveguide
                  The characteristic impedance Zo can be defined in terms of the voltage-current
ratio or in terms of power transmitted for a given voltage or a given current.
                                  Zo (V,I) = V/I
92.Why TEM mode is not possible in a rectangular waveguide?
                 Since TEM wave do not have axial component of either E or H ,it cannot
propagate within a single conductor waveguide
93.Explain why TM01 and TM10 modes in a rectangular waveguide do not exist.
                 For TM modes in rectangular waveguides, neither m or n can be zero because
all the field equations vanish ( i.e., Hx, Hy  ,Ey.
 and Ez.=0). If m=0,n=1 or m=1,n=0 no
fields are present. Hence TM01 and TM10 modes in a rectangular waveguide do not exist.
94. What are degenerate modes in a rectangular waveguide?
            Some of the higher order modes, having the same cut off frequency ,  are
called degenerate modes. In a rectangular waveguide , TEmn and TMmn modes ( both m ≠
0 and n ≠ 0) are always degenerate.


UNIT V-CIRCULAR WAVEGUIDES AND CAVITY RESONATORS


     95.What is a circular waveguide?
                      A circular waveguide is a hollow metallic tube with circular crosssection for propagating the electromagnetic waves by continuous reflections from
the surfaces or walls of the guide 96.Why circular waveguides are not preferred over rectangular waveguides?
The circular waveguides are avoided because of the following reasons:
a) The frequency difference between the lowest frequency on the  dominant
mode and the next mode is smaller than in a rectangular waveguide, with
b/a= 0.5
b) The circular symmetry of the waveguide may reflect on the possibility of
the wave not maintaining its polarization throughout the length of the
guide.
c) For the same operating frequency, circular waveguide is bigger  in size
than a rectangular waveguide.
97.Mention the applications of circular waveguide.
Circular waveguides are used as attenuators and phase-shifters
98.Which mode in a circular waveguide has attenuation effect decreasing with
increase in frequency?
                        TE01
99.What are the possible modes for TM waves in a circular waveguide?
The possible TM modes in a circular waveguide are : TM01 , TM02 ,
TM11, TM12
100.What are the root values for the TM modes?
                   The root values for the TM modes are:
                 (ha)01 =  2.405   for TM01
             
        (ha)02 =  5.53     for TM02
                  (ha)11 =  3.85    for TM11
                 (ha)12 =  7.02    for TM12
101.Define dominant mode for a circular waveguide.
               The dominant mode for a circular waveguide is defined as the lowest
order mode having the lowest root value.
      102.What are the possible modes for TE waves in a circular waveguide?
The possible TE modes in a circular waveguide are : TE01 , TE02 ,
TE11, TE12
103. What are the root values for the TE modes?
                   The root values for the TE modes are:
                 (ha)01 =  3.85     for TE01
             
        (ha)02 =  7.02     for TE02
                  (ha)11 =  1.841  for TE11
                 (ha)12 =  5.53    for TE12
            104. What is the dominant mode for TE waves in a circular waveguide
                The dominant mode for TE waves in a circular waveguide is the
TE11  because it has the lowest root value of 1.841  
      105. What is the dominant mode for TM waves in a circular waveguide
                The dominant mode for TM waves in a circular waveguide is the
TM01  because it has the lowest root value of 2.405.
      106. What is the dominant mode in a circular waveguide
                The dominant mode for TM waves in a circular waveguide is the
TM01 because it has the root value of 2.405. The dominant mode for TE waves in
a circular waveguide is the TE11  because it has the root value of 1.841 .Since  the
root value of TE11 is lower than TM01 , TE11 is the dominant or the lowest order
mode for a circular waveguide.
      107.  Mention the dominant modes in rectangular and circular waveguides
  For a rectangular waveguide,
              the dominant mode is TE01
  For a circular waveguide,
              the dominant mode is TE11
108.Why is TM01 mode preferred to the TE01 mode in a circular waveguide?
TM01 mode is preferred to the TE01 mode in a circular waveguide, since
it requires a smaller diameter for the same cut off wavelength.
  109.What are the performance parameters of microwave resonator?
                      The performance parameters of microwave resonator are:
(i) Resonant frequency
(ii) Quality factor
(iii) Input impedance
110.What is resonant frequency of microwave resonator?
              Resonant frequency of microwave resonator is the frequency at which the energy
in the resonator attains maximum value. i.e., twice the electric  energy or magnetic
energy.
111.Define quality factor of a resonator.
                      The quality factor Q is a measure of frequency selectivity of the resonator.
It is defined as
                Q = 2 ∏ x Maximum energy stored / Energy dissipated per cycle
                     = ω W/ P
Where W is the maximum stored energy               P is the average power loss
112.What is a resonator?
                      Resonator is a tuned circuit which resonates at a particular frequency at
which the energy stored in the electric field is equal to the energy stored in the magnetic
field.
113.How the resonator is constructed at low frequencies?
                             At low frequencies upto VHF ( 300 MHz) , the resonator is made up of
the reactive elements or the lumped elements like the capacitance and the inductance.
114.What are the disadvantages if the resonator is made using  lumped elements at
high frequencies?
1) The inductance and the capacitance values are too small as the
frequency is increased beyond the VHF range and hence difficult to
realize .
115.What are the methods used for constructing a resonator?
                             The resonators are built by
a) using lumped elements like L and C
b) using distributed elements like sections of coaxial lines
c) using rectangular or circular waveguide
116.What is a transmission line resonator or coaxial resonator?
                    Transmission line resonator can be built using distributed elements  like
sections of coaxial lines. The coaxial lines are either opened or shunted at the end
sections thus confining the electromagnetic energy within the section and acts as the
resonant circuit having a natural resonant frequency.
117.Why transmission line resonator is not usually used as microwave resonator?
                         At very high frequencies transmission line resonator does not give very
high quality factor Q due to skin effect and radiation loss. So, transmission line resonator
is not used as microwave resonator
118.What are cavity resonators?
                        Cavity resonators are formed by placing the perfectly conducting sheets on
the rectangular or circular waveguide on the two end sections and hence all the sides are surrounded by the conducting walls thus forming a cavity. The electromagnetic energy is
confined within this metallic enclosure and they acts as resonant circuits .
119.What are the types of cavity resonators?
                           There are two types of cavity resonators. They are:
                     a ) Rectangular cavity resonator
                     b ) Circular cavity resonator
120.Why rectangular or circular cavities can be used as microwave resonators?
              Rectangular or circular cavities can be used as microwave resonators because
they have natural resonant frequency and behave like a LCR circuit.
121.How the cavity resonator can be represented by a LCR circuit?
                      The electromagnetic energy is stored in the entire volume of the cavity in
the form of electric and magnetic fields. The presence of electric field gives rise to a
capacitance value and the presence of magnetic field gives rise to a inductance value and
the finite conductivity in the walls gives rise to loss along the  walls giving rise to a
resistance value. Thus the cavity resonator can be represented by a equivalent LCR
circuit and have a natural resonant frequency
122.Name the three basic configurations of coaxial resonators.
                             The basic configurations of coaxial resonators are:
d) Quarter wave coaxial cavity
e) Half wave coaxial cavity
f) Capacitance end coaxial cavity
123.What is  the dominant mode for rectangular resonator?
                            The dominant mode of a rectangular resonator depends on the
dimensions of the cavity.
For b
124.What is  the dominant mode for circular resonator?
                            The dominant mode of a circular resonator depends on the dimensions
of the cavity.
Ford< 2a, the dominant mode is TM010
125.When a medium is said to be free- space.
                   A free-space medium is one in which there are no conduction currents and no
charges.                                                        








 16 MARKS QUESTIONS




1. Explain in detail about the waveform distortion. Derive the condition for a
distortion less line?
   Waveform Distortion:
                      Signal transmitted over lines are normally complex and consists of many
frequency components. For ideal transmission, the waveform at the line-receiving end
must be the same as the waveform of the original input signal. The condition requires that
all frequencies have the same attenuation and the same delay  caused by a finite phase
velocity or velocity of propagation. When these conditions are not satisfied, distortion
exists.
                        The distortions occurring in the transmission line are called waveform                          
distortion or line distortion. Waveform distortion is of two types:
                         a) Frequency distortion
                         b) Phase or Delay Distortion.
a) Frequency distortion:
                         In general, the attenuation function  α is a function of frequency.
Attenuation function specifies the attenuation or loss incurred in the line while the signal
is propagating. When a signal having many frequency components are transmitted along
the line, all the frequencies will not have equal attenuation and hence the received end
waveform will not be identical with the input waveform at the sending end because each
frequency is having different attenuation. This type of distortion is called frequency
distortion. That is, when the attenuation constant is not a function of frequency,
frequency distortion does not exist on transmission lines.
           In order to reduce frequency distortion occurring in the line,
                        a) The attenuation constant α   should be made independent of frequency.            
b) By using equalizers at the line terminals which minimize the frequency                                                        
distortion. Equalizers are networks whose frequency and phase
characteristics are adjusted to be inverse to those of the lines, which result
in a uniform frequency response over the desired frequency band, and
hence the attenuation is equal for all the frequencies.
b) Delay distortion:
                When a signal having many frequency components are transmitted along the
line, all the frequencies  will not have same time of transmission, some frequencies
being delayed more than others. So the received end waveform will not be identical with
the input waveform at the sending end because some frequency components will be
delayed more than those of other frequencies. This type of distortion is called phase or
delay distortion. It is that type of distortion in which the time required to transmit the
various frequency components over the line and the consequent delay is not a constant.
This is, when velocity is independent of frequency, delay distortion does not exist on the
lines. In general, the phase function is a function of frequency. Since v= ω / β, it will be
independent of frequency only when β is equal to a constant multiplied by ω.              In order to reduce frequency distortion occurring in the line,
e) The phase constant β should be made dependent of frequency.    
f) The velocity of propagation is independent of frequency.        
g) By using  equalizers  at the line terminals which minimize the
frequency distortion. Equalizers are networks whose frequency and
phase characteristics are adjusted to be inverse to those of the lines,
which result in a uniform frequency response over the desired
frequency band, and hence the phase is equal for all the frequencies.
Therefore, we conclude that a transmission line will have neither delay nor frequency
distortion only if α is independent of frequency and β should be a function of frequency.
Distortion less line:  
                It is desirable, however to know the condition on the line parameters that
allows propagation without distortion. The line having parameters satisfy this condition is
termed as a distortion less line. A line, which has neither frequency distortion nor phase
distortion is called a distortion less line. The condition for a distortion less line was first
investigated by Oliver Heaviside.Distortionless condition can help in designing new lines
or modifying old ones to minimize distortion.
Condition for a distortion less line
                 The condition for a distortion less line is
                                                   RC=LG. Also,
                        a) The attenuation constant α   should be made independent of frequency.
                                               
                                                  α  =    RG              
                        b) The phase constant β should be made dependent of frequency.
                                               β  =   ω    LC
                        c) The velocity of propagation is independent of frequency.
                           V=1 /    LC
2. Explain in detail the different types of loading a cable? Derive the attenuation
and phase constant and velocity of propagation for a loaded cable.
Loading:
                     In ordinary telephone cables, the wires are insulated with paper and twisted
in pairs, therefore there will not be flux linkage between the wires, which results in
negligible inductance, and conductance. If this is the case, the there occurs frequency
and phase distortion in the line. For the telephone cable to be distortion less line, the
inductance value should be increased. Increasing the inductance by inserting inductors in
series with the line is termed as  loading and such lines are called  loaded lines. The
theory of loading was developed by Oliver Heaviside and Professor.  M.I. Pupin
developed the practical method of loading.
                       In practice, lumped inductors, known as loading coils are placed at suitable
intervals along the line to increase the effective distributed inductance. So loading is the
process of increasing the inductance value by placing  lumped inductors at specific
intervals along the line, which avoids the distortion.
 
   Loading Coils:                        The important aspect of a loading coil design is that saturation and stray
fields should be avoided. It should have a low resistance and should be of small size
particularly for the field work. It should maintain circuit balance. For this reason, the
coils are wound on toroidal cores( See figure from Umesh Sinha Book).These cores are
manufactured by permalloy or molybdenum-permalloy,ground to dust and then hold
together like shellac, so that there are a large number of air gaps to reduce the possibility
of saturation.
  Types of Loading :  
                     a) Continuous loading
                     b) Patch loading
h) Lumped loading  
i)
           Continuous loading is the process of increasing the inductance value by placing a
iron core or a magnetic tape over the conductor of the line thus increasing the
permeability of the surrounding medium thereby increasing inductance.  (Refer fig. From
Umesh Sinha Book)
            Patch loading is the process of using sections of continuously loaded cables
separated by sections of unloaded cables that increases the inductance value.
            Lumped loading is the process of increasing the inductance value by placing
lumped inductors at specific intervals along the line, which avoids the distortion.
   
 
Attenuation and phase constant for a loaded cable:
           For a uniformly loaded cable,
                       a) The attenuation constant α   is
                                                   α  =  ( R/2) *      C/L          
                        b) The phase constant β is
                                                 β  = ω    LC
                        c) The velocity of propagation is
                           V=        1 /  LC
3. Derive the general solutions of transmission line Defn: used for guiding electrical signals
Write the general solutions: the votage and current equation
4. Derive the input impedance of a transmission line. Also find the input
impedance of open and short circuited lines.
1.Input impedance is voltage divided  by current
2.write the condition for a short circuited line and determine the input
impedance
3. write the condition for a open circuited line and determine the input
impedance
5. Derive the reflection loss of a transmission line
                Reflection occurs because of the following cases:
                       1) when the load end is open circuited
                       2) when the load end is short-circuited
                       3) when the line is not terminated in its characteristic impedance
        When the line is either open or short circuited, then there is not resistance at the
receiving end to absorb all the power transmitted from the source end. Hence all the
power incident on the load gets completely reflected back to the source causing
reflections in the line. When the line is terminated in its characteristic impedance, the
load will absorb some power and some will be reflected back thus producing reflections.
                Reflection loss is defined as the number of nepers or decibels by which the              
current in the load under image matched conditions would exceed the current actually
flowing in the load.
           6. What are impedance matching devices.Write short notes on eighth line and half
line.
Answer:
           The Eigthwave, half wave, quarter – wave line or transformer and the
tapered line are some of the impendence –matching devices.
Half wave line:
            The expression for the input impendence of the line is given by
                                     Zs  =  Zr
Thus the line repeats is terminating impedance .Hence it is operated as one to one
transformer .Its application  is to connect load to a source where they can not be
made adjacent.
Eigth wave line: An eighth wave line is used  to transform any resistance to an impendence with a
magnitude equal to Ro of the  line  or to obtain a magnitude match between a
resistance of any value  and a source of Ro internal resistance
          7.      Write short notes on quarter wave line and write its applications.
Answer:
The expression for input impendence of a quarter wave line is given by
                                         Zs = R0
2
                                                  
                                                    Zr
Hence the quarter  wave line is considered as a transformer to match impedances
Zr and Zs .It is used as a impendence matching section .
The important application of quarter wave line is to a couple  a transmission line
to a resistive load such as antenna.
A short circuited quarter wave line can be used as an insulator to support an open
wire line or coaxial line conductor .
An important  application  of the quarter wave matching sectionis to  a
couple a transmission line  to a resistive load such as an antenna .The quarter –
wave matching section then must be designed to have a characteristic impendence
Ro so chosen that the antenna resistance Ra is transformed to a value equal to the
characteristic impendence Ra  of the transmission line.The characteristic
impendence  Ro of the matching  section    then should be
                         Ro’ = √ Ra Ro
8.Write short notes on exponential line for impedance transformation.
          The equations used for the design of the exponential line are :
                   
                   L/L1 = ln(d/a)/ln(d1/a1)                                                                          
Where, L is the inductance per meter of the line
             L1 is the inductance per meter at the sending end.
9.Explain in detail about single stub matching.
Single stub matching is one in which single stub is placed in shunt with a
main transmission line to provide impedance matching
10.Explain in detail about double stub matching.
Another possible method of impedance matching is to use two stubs in
which the locations of the stub are arbitrary,the two stub lengths furnishing the
required adjustments.The spacing is frequently  made  λ/4.This is called double
stub matching. 11.Derive an expression for the voltage and current on the dissipation less line.
Answer:
 Refer page No:285 (Text book)
12.Derive an expression for the input impedance under  open and short circuited
condition.
Answer:
The input impedance of open aned short circuited lines are given by,
  Zsc = jRo tan
2 πs
                                                                                           
λ
13.Derive an expression for the input impedance of the dissipation less line.
Answer:
The input impedance of a dissimpationless line is given by,
 
 Z
s
 =  Es
  = R0  1+  k < φφφ -2βββs
                     I
s
           1-  k  <φφφ -2βββs
14.What are standing waves? Derive the expression for standing wave Ratio.
Answer:
If the transmission is not terminated in its characteristic impedance ,then there
will be two waves traveling along the line which gives rise to standing waves
having fixed maxima and fixed minima.
The ratio of the maximum to minimum  magnitudes  of voltage or current on a
line having  standing  waves called standing  waves ratio.
                                                 Emax        Imin
                                    S =                  =    
                Emin         Imin
15. Derive the field component of the wave propagating between parallel planes?
• Definition for Parallel guide
• Expression for Ex,Ey,Hx,Hy
16. Derive the electromagnetic field expressions for TE waves guided by a parallel
conducting plane?
• Definition for TE waves
• Expression for Ey,Hx,Hz
17. Derive the electromagnetic field expressions for TM waves guided by a parallel
conducting plane?
• Definition for TM waves • Expression for Ex,Ez,Hy
18. Derive the electromagnetic field expressions for TEM waves guided by a parallel
conducting plane?
• Definition for TEM waves
• Expression for Ex,Hy
19.Derive the field expressions for the field components of  TM waves in a
rectangular waveguide
 For TM waves, Hz=0
 Substitute Hz=0 and find the field components Ey, Hx, Hy ,Ez , Ex
 
20.Derive the field expressions for the field components of TE waves in a
rectangular waveguide
 For TE waves, Ez=0
 Substitute Ez=0 and find the field components Ey, Hx, Hy ,Hz , Ex
 
 

by Vinoth · 0



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