Alignment Method:
BFO/Carrier Oscillator:
There are several ways to adjust the BFO/Carrier Oscillator frequency.
1. Rough alignment may be made by adjusting C-72 while listening to a received SSB
signal on 20 meters. This is a two-handed operation as you have to use the VFO Fine
Tuning to keep the VFO frequency set for best intelligibility while searching for the
best quality audio with C-72.
2. Instrument alignment is done by monitoring carrier attenuation while adjusting the
BFO/Carrier Oscillator relative to the crystal filter sideband shape factor. The oscillator
frequency needs to be 24 to 40 db down the lower side of the filter passband.
●
Disconnect the microphone or short it's audio output so that there is no
audio coming through the microphone amplifier.
●
Set up an oscilloscope or RF detector and voltmeter to monitor the
transmit 2
nd
IF amplifier output (the exposed lead on R-45, near Q-10).
●
Connect a frequency counter to the exposed lead of R-67 to monitor
BFO/Carrier Oscillator frequency.
●
Operate the PTT switch and un-balance the balanced modulator by
turning R-66 until you have a measurable signal. Un-key the transmitter.
●
Key the transmitter again and adjust the BFO/Carrier Oscillator frequency
(C-72) for maximum signal level, note the frequency on the counter, and
then adjust C-72 for a lower frequency and a 24 to 40 db decrease in
monitored signal level. Un-key the transmitter. The BFO/Carrier
Oscillator frequency needs to be just outside the lower frequency edge of
the crystal filter for USB operation.
●
Disconnect the frequency counter, key the transmitter and re-check to see
that you are still at the same signal attenuation point on your scope or
voltmeter. Un-key the transmitter. This checks to make sure that your
counter was not pulling the BFO/Carrier Oscillator off frequency by any
significant amount.
●
Key your transmitter and adjust the modulator balance (R-66 and C-65)
for minimum RF indication. Un-key your transmitter.
●
Re-connect your microphone or remove the short from it's output.
There are several additional ways to adjust the BFO/Carrier Oscillator frequency. If you have
the knowledge and equipment it might be an interesting exercise to try these methods as well.
However, even the Rough Alignment method outlined above will usually provide adequate
setting for good reception and transmission.
VFO:
VFO components provided in the kit have been chosen in an attempt to insure that your tuning
range will be within the 20 meter band. However, this is not guaranteed. You should check the
VFO frequency with a counter connected the exposed lead of R-27, or use a well calibrated
receiver. Trimmer capacitors on the back of the main tuning capacitor will provide some
adjustment but you will need to select which capacitor sections are connected to set the
minimum & maximum tuning limits and the tuning range.
