[HBR] Negative temp compensation capacitors

[N2EY at aol.com]

In a message dated 1/29/08 5:00:57 PM Eastern Standard Time, 
amargosaent at iscweb.com writes:


> Has anyone on the reflector identified a source for negative temp 
> coefficient capacitors in the N750 range available in small capacitance 
> ranges (e.g., 1 pfd through 20 pfd in 1  and 2 pfd steps)? 

Not really, but I do know a trick, learned from master receiver builder W2LYH 
and others.

I presume the temp comp is for an oscillator. 

The trick is to first get the oscillator working without temperature 
compensation, and see that it drifts downward in frequency with increasing 
temperature, which would mean it needs negative temperature compensating capacitance.

Then add "too much" negative temperature compensating capacitance so that it 
drifts the wrong way.

The trick is that an air trimmer cap is then installed in series with the 
temperature compensating capacitor so that the amount of compensation can be 
adjusted. Of course a fixed NPO capacitor can be substituted once the exact value 
is known, but that's an extra step which requires a wide selection of NPOs.

73 de Jim, N2EY


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