FMT 25 SERIES HANDBOOK.pdf


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FMT25
ALIGNMENT PROCEDURE

TEST EQUIPMENT REQUIRED











RF power meter capable of 30W at 100MHz
30W dummy load 50 Ohm
Digital multimeter
Low distortion audio oscillator capable of +12dBm 600 Ohm, balanced
Deviation monitor
Noise and distortion test set
FM receiver/demodulator
Stereo demodulator test set
Digital frequency counter
Spectrum analyser

TRANSMITTER
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

Connect power meter and dummy load to Antenna socket, select appropriate power range.
Select the desired frequency using the rotary switches on the exciter board.
Connect 240VAC supply and switch on transmitter.
Adjust power level by adjusting RV90 on the exciter board.
Trim the carrier frequency by adjusting C29 on the exciter board. This should be done after allowing
an adequate warm up period.
Connect the spectrum analyser to sample the RF output and confirm that the second and third
harmonics are no greater than 63dBc below carrier.
Connect the deviation monitor to sample RF output and set the carrier frequency.
Connect a precision receiver/demodulator and Noise and Distortion test set to sample RF output and
set to carrier frequency.
Connect the audio generator to the balanced audio inputs and set for 400Hz at the desired input
level. Adjust VR1 in the exciter board to achieve the required deviation level. NOTE: there is no level
control for the MPX input.
Confirm the signal to noise ratio is greater than 65dB after replacing main lid of the transmitter.

METER ADJUSMENTS
The calibration controls for the front panel meter are located on the back of the meter function switch
on the front panel. Connect an external wattmeter and dummy load to the transmitter and adjust to the
required power output. Adjust RV4 on the meter function switch board (0207B) so the front panel meter
reads 0dB on the forward power setting.
The reverse power metering is calibrated by setting RV3 to the same position RV4. This relies on the
forward and reverse detectors being symmetrical. Follow the following steps;
1.
2.
3.
4.

Set front panel meter switch to forward power.
Measure resistance between METPOS and TP1 on board 0207B.
Set front panel meter switch to reverse.
Measure resistance between METPOS and TP2 on boars 0207B and adjust RV3 to read the same
resistance as in step 2.