Re: question about crystal spacing in filter

ajparent1 <kb1gmx@...>
 

My comments at bottom.

--- In BITX20@..., Rahul Srivastava <vu3wjm@y...> wrote:
Hi!

Some one once mentioned , thumbrule for xtal matching was within 10%
of the required BW. However I try to keep it within 100hz for SSB filters.

Till date all appear to have worked fine.

73

Rahul VU3WJM

PS: I make the BFO first and with 33pf in series with xtal measure
all available with me. Select ones within 100hz of each other . Take
the lowest one for carrier osc for BITX , takes care of xtal pulling.

This is a good thing to do. Having done lower sideband by picking
a high crystal makes pulling it high easier.

One other trick. Using the BFO to pick the crystals is a good first
step. Once the filter is fabricated you can use the BFO to sweep the
filter to assess the filter shape and bandwidth. Usually that
requires tacking on a coil and larger tuning capacitor temporarily.


Allison
KB1GMX

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