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Hi again

My homebrew (scratch built) G6LBQ BiTx txcvr is assembled and in debug stage. Overall, I'm pleased with the results, the Rx has lots of gain and the AGC works well.? I routinely enjoy listening to US amateurs on 7.150 to 7.170 in my evenings here (VK3), despite the quite poor band conditions being experienced around the world right now.??

My build is:

- Arduino Nano/LCD/si5351 with a single broadbanded 2n2222 buffer/amp for both VFO and BFO
- TDA2003 replaces LM386
- IF is 9MHz
- 5 (not 6) crystals in the filter, capacitors are 68p and 82p, couplings are the original 100p, the filter is a little bassy so I will experiment with some smaller values to move the passband a bit higher
- PA uses one RD16HHF1 (not two in push pull) in a standard QRP 5W PA circuit
- For T/R switching, one digital input on the Nano senses the PTT switch going low, then raises another digital output, which pulls in the two relays on the PA board; one relay has a set of contacts that switch 12v between the low level stages of the Rx and Tx.??
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Otherwise it is exactly as per the MkII circuit diagram.? The build is on a hand drawn PCB that is mostly ground plane, and with surface mount parts.? The Exciter board is bolted tightly to an aluminium case lid. The MC1350 took a few tries to get aligned, it was distorting until I got the tuned circuit on its output pins close to resonant, but now the receiver sounds clean and shows no signs of instability.??

Back on the AGC, mine is not quite adjusted right yet, the no-signal voltage is too low, so when you turn on the AGC the receiver noise level drops too far. The AGC action is good on strong signals.??

The curious thing is that when I press PTT there is a sharp chirp of audio generated.? It is as loud as the subsequent spoken voice, starts off about 1khz and drops quickly, lasting about 100-200mS.? It is prominent enough that it will draw comments from other stations in a QSO.? It? suggests an electrolytic capacitor charging/discharging.? I removed the 50uF supply filter cap on the mic amp -- no difference.? I reduced the 10u in series with the mic amp hot input to 2u, no change.?
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If I manually switch the rig to Tx it still happens, so it might have something to do with power switching between Rx and Tx.?
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Just wondering if anyone has seen this.?

The Tx is working too, but becomes unstable with the PA bias above about 400mA, so it needs better shielding, I'll spend some quality workshop time with hacksaw file and PCB stock to create some compartments inside the box.? ?

73 Paul VK3HN.? ?