To Study The Characteristics Of Reflex Klystron

AIM:

To study the characteristics of the reflex Klystron tube and to determine its electronic tuning range.

APPARATUS REQUIRED:

Klystron Power Supply, Klystron Tube, Isolator, Frequency Meter, Variable Attenuator, Detector
Mount, Waveguide Stand, VSWR Meter and BNC Cable.

THEORY

The Reflex Klystron makes use of velocity modulation to transform a continuous electron beam into microwave power. Electron emitted from the cathode are accelerated and passed through the positive resonator towards negative reflector, which retards and, finally, reflects the electron; and the electron turns back through the resonator. Suppose an hf-field exists between the resonator, the electron travelling forward will be accelerated or retarded, as the voltage at the resonator changes in amplitude. The accelerated electrons leave the resonator at an increased velocity and the retarded electrons leave at the reduced velocity. The electrons leaving the resonator will need different time to return, due to change in velocities. As a result, returning electrons group together in bunches. As the electron bunches pass through resonator, they interact with voltage at resonator grids. If the bunches pass the grid at such time that the electrons are slowed down by the voltage, energy will be delivered to the resonator; and Klystron will oscillate.  the schematic of a typical Klystron tube. the relationship between output power, frequency and reflector voltage. The frequency is primarily determined by the dimension of resonant cavity. Hence, by changing the volume of resonator, mechanical tuning range of Klystron is possible. Also, a small frequency change can be obtained by adjusting the reflector voltage. This is called Electronic Tuning Range. The same result can be obtained, if the modulation voltage is applied on the reflector voltage VR 

PROCEDURE:

(a) Carrier Wave Operation
1. Connect the components and equipments 
2. Set the Variable Attenuator at the maximum position (a zero micrometer reading).
3. Set the Mod-Switch of Klystron Power Supply to CW position, beam voltage control knob to fully anticlockwise and reflector voltage control knob to fully clockwise and the Meter Switch to ‘OFF’position.
4.Rotate the knob of frequency meter at one sidefully.
5.Put the multimeter in dc microampere range of 250 microampere.
6. ‘ON’ the Klystroiz Power Supply, VSWR Meter and Cooling Fan for the Klystron tube.
7. Put the meter switch to beam voltage position and rotate the beam voltage knob clockwise slowly upto 300 V meter reading, and observe beam current on the meter by changing meter switch to beam current position. “The beam current should not increase more than 30 mA”
8. Change the reflector voltage slowly and watch on the micro. Set the voltage for maximum deflection in the meter. If no deflection is obtained, change the multimeter switch position to 50 microampere.
9. Tune the plunger of Klystron Mount for the maximum output.
10. Rotate the knob of frequency meter slowly and stop at that position, when there is less output current on multimeter. Read directly the frequency meter between two horizontal lines and vertical marker. If micrometer type frequency meter is used, read the micrometer reading and find the frequency from its calibration chart.
11. Change the reflector voltages and read the current and frequency for each reflector voltage and plot the graph 
(b) Square Wave Operation
1. Connect the equipments and components 
2. Set the variable attenuator to around zero position.
3. Set the range switch of VSWR meter at 40 db position, input selector switch to crystal impedance position, meter switch to normal position.
4. Set Mod-Selector switch to AM-MOD position, beam voltage control knob fully anti-clockwise direction, reflector voltage control knob to the maximum clockwise position and meter switch to OFF U position.
5. ‘ON’ the Klystron Power Supply, VSWR meter and cooling fan.
6. Change the meter switch of Klystron Power Supply to beam voltage position,and rotate the beam voltage knob clockwise up to 300 V deflections in meter.
7. Keep, the AM-MOD amplitude knob and AM-FRE knob at the mid- position.
8. Rotate the reflector voltage knob anti-clockwise to get deflection in VSWR meter.
9. Rotate the AM-MOD amplitude knob to get the maximum output in VSWR meter.
10. Maximize the deflection with frequency control knob of AM-MOD.
11. If necessary, change the range switch of VSWR meter to 30 db or 50 db if the deflection in VSWR meter is out of scale or less than normal scale respectively. Further, the output can also be reduced by Variable Attenuator for setting the output for any particular position.
12. Find the oscillation frequency by Frequency Meter as described in the earlier set-up.
13. Observe the square wave modulation of the Klystron on the CRO
(c) Mode Study on Oscilloscope
1. Set up the components and equipments 
2. Keep position of variable attenuator at ten positions.
3. Set Mod selector switch to FM-MOD position with FM amplitude and FM frequency knob at mid position, keep beam voltage control knob fully anti-clockwise and reflector voltage knob to fully clockwise with meter switch to ‘OFF’ position.
4. Keep the time/div. scale of oscilloscope around 100 Hz frequency measurement and volt./div. to lower scale.
5. ‘ON’ the Klystron Power Supply and Oscilloscope.
6. Change the meter switch of Klystron Power Supply to Beam Voltage position and set beam voltage to 300 V by beam voltage control knob.
7. Keep Amplitude knob of FM Modulator to maximum position and rotate the reflector voltage anti-clockwise to get modes P3 on the oscilloscope. The horizontal axis represents reflector voltage axis, and vertical axis represents output power.
8. By changing the reflector voltage and amplitude of FM modulation, any mode of Klystron tube can be seen on Oscilloscope.

OBSERVATIONS:
Beam Voltage =
Repeller Voltage =
Tabular Form                         

RESULT:
The characteristic of Reflex Klystron has been studied and modes have been
found.

PRECAUTION:

1.klystron power supply should be constant.
2.BNC cable should be connected properly.
3.VSWR meter readings should be taken carefully.