Varactor Crystal Set video

I did do a little more testing on the 1SV149 varactor diode from the previous blog:

https://wb9kzy.blogspot.com/2024/07/b-cap-meter-has-feet-of-clay.html

The part does basically meet the spec, 25 pF at 8 volts and 396 pF at 1 volt.  Need to realize that the actual 1sV149 values are a little higher due to the series .01 uF cap.

However the crystal set didn't work that well, kind of a lousy response with an antenna coil out of an old GE tube radio.  Only got one station at 680 kHz (WDBC) and that didn't really peak like it should.  Then I did a little searching and found this video by Mikrowave1:

source: https://www.youtube.com/watch?v=AaPdHu-Dsio

He uses two varactors with the cathodes connected (a series circuit) which eliminated the need for the .01 uF DC blocking cap of the W0XI circuit with the single varactor.  However it also halves the resulting capacitance so with a crystal set the coil value must be larger.  He uses this design:

I will have to scare up another 1sv149 and get a coil similar to 427 uH made up and try it.  I think I have some suitable cardboard tubes from Saran wrap that are 2 inch diameter:

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm