The AM Forum

I'm working on a homebrew superhet receiver for 40 meters, and now it's down to figuring the coils for tracking.

I want to use a broadcast receiver tuning capacitor, but I don't know the values of the sections. One section is presumably something like 15-365pf for tuning ~500Khz-1600Khz, but the other (smaller) section is ??

Any common combinations that anyone can come up with? I plan to measure the sections, but don't have the test oscillator set up yet. A few ballpark figures to compare my results to would be great.

There's a handy online calculator for superhet tracking
http://ironbark.bendigo.latrobe.edu.au/~rice/superhet.js/superhet.html

If you're into building, this is a handy gizmo for the bench:

http://www.aade.com/lcmeter.htm

Jonnie's caculator appears to require both ant. and osc. cap sections to be the same. , i. e., say 365pf.   I measured the old Ocean Hopper var cap. with two dissimilar sect. and found 468 and 216 pf including about 40 pf stray from leads.  The tracking calc's for sections not the same are more involved.  All my references assume two sections the same.   Might be better to buy a two or three section var. (all same) from Antique Radio or similar.  Be cleaner connections too than our old stuff contact wise, etc.  The commercial boys found adequate tracking w/o additional padding caps on all American fives,  I guess; -anything to save a penny.