On frequency!

Finally!

I put a 68 pF capacitor in series between the tuning capacitor, C12, and existing 68 pF capacitor, C10. That seems to have dragged the operating frequency sufficiently high to hear some signals. The oscillator circuit now looks like this:

Truth be told, to get up to the phone portion of 40 meters with this oscillator, I had to crank the T2 tuning slug ALL the way up, perhaps more than I really should, but it works. Currently, I'm covering 7,150.5 kHz up to 7,242.5 kHz according to my Si5351 signal generator (hooray for homebrew test equipment!).

I'm thinking I'll replace the two series 68 pF capacitors at some point with a single capacitor, perhaps in the 10 pF to 20 pF range to get the same coverage without putting the tuning slug up against the stops. There's also another reason to replace them: this receiver is drifty as hell right now. I couldn't figure out why it wouldn't stay on frequency, as I was seeing several tens of Hertz drift per minute. After a good bit of head scratching, I looked over my parts list and it turns out that all of the other oscillator caps are NP0 or COG, except for my 68 pF ones. D'oh!

The section on oscillators in "Experimental Methods in RF Design" needs some reviewing this evening. I'm not satisfied with the limited 92 kHz band spread that I'm getting out of this oscillator; it seems like I should be able to get more range of tuning. Without replacing it with an Si5351, I want to try and experiment with changes to the oscillator to get more spread, and I'll write up what I find.

Another area I'd like to experiment with is the "filter" between the mixer and the audio section. There's an awful lot of signals close together out there, and tuning or discerning one from the other is a pain. I ran a quick LTspice model on the components playing at being a filter, and it would seem that they do nothing of the sort. In fact it would seem that they actually attenuate audio below about 3 kHz. Not, I think, what I need for selectivity.

For anyone interested, I put together a short video of me sweeping the band. The audio isn't terribly great, and I think there was entirely too much interference, but I'm pleased to hear some QSOs out there today.

The first signals I heard were a round table of sorts on 7,185 kHz, with KK6TS, K6DNS, and W6NYW. Thanks to them for helping me, unknowingly, to validate my new receiver. I also got to spend some time listening to what I believe the participants called the "Do Nothing Net" on 7,222 kHz.

Let me know what you think...I really would appreciate the feedback.