Re: Air capacitor vs plastic capacitor


Rik
 

Hi Max- I am not very knowledgeable, but my understanding is for the whole tuned circuit to be high Q, both the coil and cap would have to be, and there could not be any cold solder connections or poorly routed wires or anything else I am not aware of in the shape and connections of the circuit which lowers Q.

For the coil, the highest count Litz really helps, and some caps are rated much higher than others. Without Litz, spacing out the turns  or basket weaving them helps I think.

I just leave Litz  leads on my coils with copper alligator clips to attach to my caps. The same Ebay seller of Litz in California offers a Chinese Military cap which is supposed to be high Q. I have a pair of those.

https://www.ebay.com/itm/High-Quality-Variable-Capacitor-Stability-Invar-for-Crystal-Radio-Ham-NOS/161410110253?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

I don't have test equipment or the ability to use it to determine Q of a tuned circuit. What I look for is the width of dead air between two moderately strong  AM signals, 10 KHz apart here, as a measure of high selectivity. If you have a DSP portable with selectivity settings in the radio, the narrower ones will make less difference if the tuned antenna is high Q. There are probably other ways to detect better Q which others may chime in with. -FARMERIK

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