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Greetings, all ...

I have replaced my banjaxed raduino. It ran on the original firmware, and I'd applied several fixes to the Bitx40:
?- better biasing for Q16
?- N2CQR's active filter replacing R113 (worked a treat to knock back the tuning clicks)
?- 1k Vol pot wiper to U1.3
?- D7-K1 back-emf mod
?- I7SWX's de-thump AF clamp (modded to delay release on Tx-Rx)
?- 1N400x +12 to U1.6

All seemed stable until the 'fat-fingers' slip that killed the raduino ... although I got to hear my old sig.gen and a 'birdie' or two, I didn't actually hear decipherable audio ...

Meanwhile another 'fat-fingers' slip killed U2, so the new raduino's CLK0 is now driving Q7 base. There's plenty of audio, so Q8 and Q9 seem to be redundant with raduino tuning, though I still haven't actually heard decipherable audio ...

I've been struggling with hum. A major contributor was the power supply I've been using (linear 13.8V with seemingly defunct diode in the bridge), so I'm now running from a switcher (ex-USB-DVD external drive). There's still hum intermittently, but I've narrowed that down to stray pick-up from the raduino's CONTROLS loom. I still haven't connected any switches and 'stuff', so the wires as supplied are still there, but tucking them down against the metal (earthed) chassis-tray of my (otherwise plastic) housing has put that in the background. Should all unused lines here be defined with pull-ups at power-up unless otherwise assigned?

I've noted that with my ultimate aim of encoder tuning, the tuning pot? will become redundant and A7 usable elsewise ... perhaps taking on D4's duties to free that up for the enconder's 'bump switch'?

Now having installed Allard's latest firmware (first time and painless) I find the tuning clicks back with a vengeance. N2CQR's active filter seemingly no longer effective versus tuning clicks ...

... and there's tuning drift. It would seem that the si5351 is being controlled in 50Hz or less steps and the display only indicating each 100Hz. Is that 100k pot too high an impedance for the raduino's input? The originally-supplied 0.1uF (104) cap is connected as before wiper-to-ground, so I'm mystified ... with multiple clicks heard per displayed change (while not touching the pot.), is there a temperature effect?

I've read that rapid discharge of +RX on TX (and vice versa?) might be beneficial. I wonder if/how this might be implemented at K1 - transistor clamps controlled from opposite contacts? Not tried, just conjecture ...
RX->TX, clamping the Rx line: D18 in the +RX line will leave C110 powering the Rx audio - what purpose does it serve? and could it be bridged? or maybe do the clamp at C110 rather than at K1 contacts? +12 has left the RX side to power the TX after all - or does de-powering U1 produce its own thump?
TX->RX, clamping the Tx line: no 'great thumping' electros or diodes, so should clamp cleanly at K1.

73 de Dex, ZL2DEX

Dex,

Put a 1K to 10K in the brown lead going to the volume control. That should get rid of the hum. It results from LM386 getting
unstable.

Raj

OK, folks - Tuning clicks conquered!
Reading back on earlier messages here, it seems the regulator 7805 deserved some attention. I had fed this via 51E to drop a few volts and 'take some heat', and put a 220uf electrolytic across its output thinking it would absorb the current spikes from the Arduino as it changed state. Given the severity of the spikes as at my last missive, it didn't, so in further experimentation I tried clip-leading a 1000uF across the 7805's input and the clicks disappeared. OK, I thought, that 220uF is doing no good where it is, let's try that on the input. Bingo! Just for good measure I put a 10nF (103) disk - just what was to hand still from the old PC PSU - across the 7805 output anyway.
I've left it at that for the night. It seems the audio is more stable too, and I've heard my first valid signals! Digital stuff down the bottom of the band. Hope is on the upsurge!

73 all, de ZL2DEX

Just a few minutes from the time you posted the above about hearing some digital, I was pumping some digital at 10 watts, from the bitx, your direction. It makes a fine data radio too. Who knows, you may have been hearing me. At least someone that direction was. Glad you're making progress, and looking forward to working you bitx to bitx in the near future.

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