22-05-2012, 01:52 PM
MICROWAVE & OPTICAL COMMUNICATION LAB
MICROWAVE & OPTICAL COMMUNICATION LAB.pdf (Size: 615.2 KB / Downloads: 144)
AIM:
To study the mode characteristics of the reflex klystron tube and to determine its
Electronic tuning range.
EQUIPMENT REQUIRED:
1. Klystron power supply – {SKPS – 610 }
2. Klystron tube 2k-25 with klystron mount – {XM-251}
3. Isolator {X1-625}
4. Frequency meter {XF-710}
5. Detector mount {XD-451}
6. Variable Attenuator {XA-520}
7. Wave guide stand {XU-535}
8. VSWR meter {SW-215}
9. Oscilloscope
10. BNC Cable
Block Diagram:
THEORY:
The reflex klystron is a single cavity variable frequency microwave generator of low
power and low efficiency. This is most widely used in applications where variable frequency is
desired as
1. In radar receivers
2. Local oscillator in μw receivers
3. Signal source in micro wave generator of variable frequency
4. Portable micro wave links.
5. Pump oscillator in parametric amplifier
Voltage Characteristics: Oscillations can be obtained only for specific combinations of anode
and repeller voltages that gives farable transit time.
MW& OC LAB
Klystron Power
supply SKPS-610
Klystron
Mount
XM-251
Isolator
XI-621
Frequency
meter XF-455
Variable
attenuator
XA-520
Detector
mount
XD-451
Multi
meter
VSWR
meter
SW-115
CRO
4
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Joginpally BR Engineering College (J2)
Power Output Characteristics: The mode curves and frequency characteristics. The frequency
of resonance of the cavity decides the frequency of oscillation. A variation in repeller voltages
slightly changes the frequency.
EXPERIMENTAL PROCEDURE:
CARRIER WAVE OPERATION:
1. Connect the equipments and components as shown in the figure.
2. Set the variable attenuator at maximum Position.
3. Set the MOD switch of Klystron Power Supply at CW position, beam voltage control
knob to fully anti clock wise and repeller voltage control knob to fully clock wise and meter
switch to ‘OFF’ position.
4. Rotate the Knob of frequency meter at one side fully.
5. Connect the DC microampere meter at detector.
6. Switch “ON” the Klystron power supply, CRO and cooling fan for the Klystron tube..
7. Put the meter switch to beam voltage position and rotate the beam voltage knob clockwise
slowly up to 300 Volts and observe the 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 repeller voltage slowly and watch the current meter, set the maximum voltage
on CRO.
9. Tune the plunger of klystron mount for the maximum output.
10. Rotate the knob of frequency meter slowly and stop at that position, where there is
less output current on multimeter. Read directly the frequency meter between two horizontal
line and vertical marker. If micrometer type frequency meter is used read the micrometer
reading and find the frequency from its frequency calibration chart.
11. Change the repeller voltage and read the current and frequency for each repeller
voltage.
B. SQUARE WAVE OPERATION:
1. Connect the equipments and components as shown in figure
2. Set Micrometer of variable attenuator around some Position.
3. Set the range switch of VSWR meter at 40 db position, input selector switch to crystal
impedance position, meter switch to narrow position.
4. Set Mod-selector switch to AM-MOD position .beam voltage control knob to fully anti
clockwise position.
5 MW& OC LAB
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Joginpally BR Engineering College (J2)
5. Switch “ON” the klystron power Supply, VSWR meter, CRO and cooling fan.
6. Switch “ON” the beam voltage. Switch and rotate the beam voltage knob clockwise up to
300V in meter.
7. Keep the AM – MOD amplitude knob and AM – FREQ knob at the mid position.
8. Rotate the reflector voltage knob to get deflection in VSWR meter or square wave on
CRO.
9. Rotate the AM – MOD amplitude knob to get the maximum output in VSWR meter or
CRO.
10. Maximize the deflection with frequency knob to get the maximum output in VSWR meter
or CRO.
11. If necessary, change the range switch of VSWR meter 30dB to 50dB if the deflection in
VSWR meter is out of scale or less than normal scale respectively. Further the output can be
also reduced by variable attenuator for setting the output for any particular position.
C. MODE STUDY ON OSCILLOSCOPE:
1. Set up the components and equipments as shown in Fig.
2. Keep position of variable attenuator at min attenuation position.
3. Set mode selector switch to FM-MOD position FM amplitude and FM frequency knob at mid
position keep beam voltage knob to fully anti clock wise and reflector voltage knob to fully
clockwise position and beam switch to ‘OFF’ position.
4. Keep the time/division scale of oscilloscope around 100 HZ frequency measurement and
volt/div. to lower scale.
5. Switch ‘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 300V by beam voltage control knob.
7. Keep amplitude knob of FM modulator to max. Position and rotate the reflector voltage anti
clock wise to get the modes as shown in figure on the oscilloscope. The horizontal axis
represents reflector voltage axis and vertical represents o/p power.
8. By changing the reflector voltage and amplitude of FM modulation in any mode of klystron
tube can be seen on oscilloscope.