4.1.10
FM Calibration
After the AM/FM generators are verified use these steps to calibrate the FM output.
Equipment Setup
1.
On the front panel, connect an external function generator with a BNC tee connector to
FM IN. Connect a scope to the BNC tee at channel 1. Ensure that the scope displays a
clean sine wave. A mixer with a divide by 40 output is required. Connect this mixer to
RF OUT on the front panel.
2.
Then connect the RF output of the LO signal generator to the mixer. The LO generator
is set to 4.2 GHz at +5 dBm to provide an offset. Connect the divide by 40 output of the
mixer to the 8902A measuring receiver.
3.
The divide by 40 function produces readings that are 1/40th of the actual unit deviation.
For example, the 25 kHz receiver reading in this procedure is a result of divide by 40.
4.
On the 8902 receiver, the filters are set at 50 Hz and 15 kHz. Select the FM mode.
Option: Connect Channel 2 on the scope to the modulation output on the receiver.
FM External Procedure
1.
Select FM EXT at 1 MHz deviation.
2.
Use the external generator to apply a 1 kHz sine with 2 Vpp at FM IN. Measure the sine
wave on the scope to ensure accuracy.
3.
Select the frequencies listed in Table 4-5 in order and adjust the specified pot, if
required for 25 +0.05 kHz.
☛
NOTE:
The 1 GHz test step is a functional test only.
Frequency (GHz)
A18 Pots
LO Freq (GHz)
4
R33
4.2
12
R34
12.2
22
R35
22.2
FM Internal Procedure (Option 24 only)
1.
Select 4 GHz. Then enter FM INT SIN with a 1 MHz deviation and at a 1 kHz rate. Set
the LO generator for 4.2 GHz.
2.
On A6-A1, if required, adjust R13 for a reading of 25 kHz +0.05 kHz.
3.
Select the triangle mode. Wait approximately 20 seconds for the signal to settle. Verify
that the reading is 25 kHz +0.05 kHz.
4.
Select FM INT SQR at a rate of 8 kHz. On the receiver, enable the 20 kHz filter. On
A6-A1, if required, adjust R18 for a receiver reading of 25 +0.05 kHz.
Table 4-5. FM External Frequency Adjustment
Calibration and Testing
Manual No. 120AM00250, Rev C, September 1998
4-9
Summary of Contents for GT 9000
Page 12: ...Series GT 9000 Microwave Synthesizers x Manual No 120AM00250 Rev C September 1998 ...
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