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I finished the last board of the Soldersmoke direct conversion receiver today: the 40m band pass filter. Only, I didn’t have the specified type 6 toroids. I had T68-2s, though. In the end I ended up designing my own 40m band pass filter with totally different values. Took me all afternoon, but I ended up with a very solid result! Very low loss, acceptable match.

Look at those big Soviet trimmers in there. Tested them with the NanoVNA and they are very close to spec. #AmateurRadio #HamRadio

NanoVNA screen zoomed into the pass band, showing that the 40m band is well covered.

NanoVNA screen showing filter performance. Blue line shows pass band and extremely low loss. Yellow is SWR and reasonable. Green shows Smith chart performance.

40m band pass filter on copper clad board, using T68-2 toroids and Soviet trimmer capacitors.

Gary @N8DMT

@n8dmt@mastodon.radio replied · 3 weeks ago

@relistan Nice! A great challenge and ultimately a success. Glad you had the time and test equipment to learn what needed to be learned to make this work in a reasonable time. (Imagine completing this with only a scope and a non-sweep signal generator. Those were the old days.) On to the next phase!

Karl Matthias 🇺🇦

@relistan@mstdn.social replied · 3 weeks ago

@n8dmt thank you! Yeah, without that NanoVNA this would have been total guesswork. We live in good times for test equipment at least. Now just to get that rig receiving.

Karl Matthias 🇺🇦

@relistan@mstdn.social replied · 3 weeks ago

@n8dmt I keep looking at that 1.2 SWR and near match and thinking that one more winding of that yellow wire might knock that down to 1:1. Wondering how much patience I have to go back at it!

Gary @N8DMT

@n8dmt@mastodon.radio replied · 3 weeks ago

@relistan Wouldn’t worry too much about that at the moment (unless every thing else is working smoothly). Perfect is the enemy of the good!

Not sure you’ll ever see any difference in your RF chain’s performance…

Karl Matthias 🇺🇦

@relistan@mstdn.social replied · 3 weeks ago

@n8dmt Yeah that's all good advice. At some point, for science, I may give it a shot. If I can get the rest of this rig working... spent another hour on it tonight debugging and I can't see anything wrong.

Gary @N8DMT

@n8dmt@mastodon.radio replied · 3 weeks ago

@relistan Have a Si5351, NanoVNA and a TinySA, right?
Front-end amplifying?
LO at proper frequency and drive level?
Mixer products (pre-filter) looking OK (LO leakage, LO+RF, LO-RF all present for superheterodyne architecture?)
Post mix filter showing reasonable IF signal and level at In and out?
Si5351 gen into detector input gives audio output/change? (Not sure if your RCVR is AM, FM, SSB/CW or ?)
Audio amp thumps/hums with finger on input line? (Old school test…)
Persistence & patience… :-)

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