Just 'cause it looks pretty...

...and it does look pretty, it just still isn't working.

I was thinking on my problem from last evening on the commute home this evening, particularly the symptom wherein the peaking capacitor on the RF input tuned circuit seemed to have no effect on the received signal. What I hadn't mentioned in the last post was that the tuning slug in the 10.7 MHz IF transformer did change the received signal, albeit not enough to copy any useful signal.

What, I thought, would be the effect if I had soldered the leads for the peaking capacitor to the wrong transformer leads? The front end is balanced feed into the NE602 inputs on pin 1 and pin 2, but oddly enough the peaking capacitor which supplements the transformer's internal 47 pF capacitor is specified to be from the mixer pin 1 to ground (vice across the balanced inputs). One could assume that putting the variable capacitor from pin 2 to ground would work as well, no? It turns out, not so much.

It may be difficult to make out in the photograph, but the green/black pair of leads, which run from the peaking capacitor, runs to the transformer pad on the lower right of the can, which is then connected (by the green jumper) to the NE602 pin 2 RF input B. A few short minutes to heat up the soldering iron, and it's now on pin 1, RF input A, as the design called for in the first place.

Now that that is properly placed, the front end has positive tuning ability via the peaking capacitor, and I now understand the purpose of the potentiometer on the primary side of the input transformer...the audio output of the receiver is now quite loud, louder than I would like to have jacked into my headphones for any significant length of time. The potentiometer was omitted during construction to simplify my prototyping and to have one less thing dangling from leads off the board (currently I have the big tuning cap, the peaking cap, the headphone jacks, the antenna/ground leads, and the battery pack). After I pack the munchkins off to bed later tonight, that potentiometer will be soldered into place.

This still hasn't fixed the problem of receiving useful signals here, but that may have been due to me having the antenna wadded up under the workbench in the garage with fluorescent lights running overhead. I'll take it out to the patio later for some real testing with a real-ish antenna.

Incidentally, does anyone know how many turns the 42IF123 tuning slug is capable or moving?