Having concluded that I was significantly short on overall receiver gain, I went in yesterday and changed my AF amp from a 40db direct-coupled circuit to a 100db Darlington pair. I immediately noticed a big increase in audio output.
I did a quick receiver alignment using my Arduino/AD9860 sig generator. First I determined the actual bandpass of the crystal filter: 4.998170 MHz -- 5.000960 MHz. Using a freq counter, I set the BFO at 5.00126. I immediately started hearing 17 meter SSB signals from the West Coast. That's always a nice moment: first signals through a new receiver. Kind of like "first light" in a new telescope. Even with the filter ripple, it sounds great.
I think I'm still significantly short of gain. Audio is still faint. I notice that in the BITX17A they have added a second transistor (Q17) in the second RX receive amp. Maybe I should try something similar. Or should I add some gain in the audio chain?
I'm really enjoying this BITX project.
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Re: 20 meter AM in 2024
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I just had a QSO on 20 meter AM! The station was KA1BWO in Idaho. The
frequency was about 14,160.
I used to operate 20 meter AM in the 60s and 70s all the t...
2 hours ago