[Hallicrafters] rubberizing crystals

[Glen Zook]

A capacitor in parallel will always lower the frequency.  Putting an inductor and a variable capacitor in series with the crystal (that is crystal to inductor to variable capacitor) will make it variable over a much wider frequency range which includes both plus and minus frequencies.  I believe that if you want just to go higher in frequency then you need to use an inductor.

You can vary the frequency of a crystal like the FT-243 by varying the pressure on the crystal itself.

Glen, K9STH

Website:  http://k9sth.com


--- On Fri, 11/21/08, Nash4447 at cs.com <Nash4447 at cs.com> wrote:

From: Nash4447 at cs.com <Nash4447 at cs.com>

Hi Gang  - got a technical question for all you whizbangs out there in hamland.
 
Lets say you have a crystal that for whatever reason is not on frequency - off a bit.
 
I have seen some sets where a fixed or trimmer cap is installed either in parallel with the xtal or in series with the xtal. What is the significance of each of these two possible arrangements?  Does one method move the freq up and the other down? Also, I have seen some sets where a slug tuned coil is in series with the xtal for making frequency adjustments.   Is this supposed to move the freq up or> down?
 
I haven't found anything definitive on the web about tweaking xtal frequencies.