Ethan,
The reason you are to first tune the BPF during receive is to get them
close to the correct settings.
You should find the peak during transmit close to the peak observed
during receive.
Certainly some of the BPF inductors and capacitors could be tuned to an
improper mixer product if adjusted farther from the correct point. You
have the VFO frequency which is 4913 kHz away from the correct frequency
and any harmonic of the BFO that could be present in the RF content
prior to the BPF. There will also be other mixing products that you
could tune the BPF to (but you shouldn't). The purpose of the BPF is to
eliminate the undesired mixer products.
When tuning the BPF on TX, start with the power set between 1.5 and 2
watts. If it climbs above about 5 watts, exit TUNE and re-enter to
bring the power down again and continue to find the peak.
73,
Don W3FPR
On 2/7/2014 9:00 AM, Ethan Miller K8GU wrote:
All,
I breathed life into K2/10 #7372 (love that serial number) last night.
This is going to be fun little radio despite being a 15-year-old
design!
I noticed one thing that I wanted to ask the assembled experts here:
When peaking the TX BPF capacitors, there was a perceptible and
easily-found peak; but, if I got off the peak too far, the transmitter
power would increase rapidly to >10 watts as I tuned in the wrong
direction. This must be normal or expected? I did not monitor the
transmitter spectrum while doing this, so I don't know if it's a loud
spur that's normally suppressed or an amplifier somewhere is
conditionally-stable?
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