Adjustments
7-20 HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual
Exciter output transformer balance
1 08-04962
Alignment should only be necessary if the mixer IC5 or transformer T1 on the
Rx/Exciter PCB have been replaced. To perform the alignment use a spectrum
analyser. (For 08-05322 assemblies, R22 should be set to its mid-range position.)
q Select test channel 21 (27 MHz).
q Connect a 50 Ω dummy load to the antenna connector complete with a
power meter.
q Connect a spectrum analyser via a 47 kΩ resistor to the antenna connector.
q Set up the spectrum analyser as follows:
Centre frequency
27 MHz
Frequency span
20 kHz
Vertical level
10 dB/div
Trigger
Continuous sweep
Video bandwidth
300 Hz
q Apply a two-tone audio signal of 700 Hz and 2300 Hz at a level of 20 mV
RMS to the microphone input connector and select PTT (Transmit mode).
q Adjust the two-tone 27 MHz signal displayed on the spectrum analyser to
the top of the screen.
q Remove the 2300 Hz tone and adjust the remaining 700 Hz tone for the
same level produced by the two tones.
q Reset the spectrum analyser centre frequency to 18 MHz.
q Adjust R22 for a minimum 18 MHz signal.
It may be necessary to solder link to C55 or C56 (never both together) to
improve the balance. The unwanted 18 MHz product should be greater than
60 dB below the 27 MHz signal.
q Re-seal R22.
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