Re: UBitx Crystal filter capacitor Q

Rahul Srivastava <vu3wjm@...>

>>do we want hi or low Q?

It is  advisable to use High Q capacitors in filter circuits as well as use of high Q crystals.

>>how is the “response” better?

Response is better in terms of filter skirt resulting in a better shape factor, lower losses and over all a better performing filter.. In my experiments I have noticed a major impact on the rounding off at the filter bandpass edges. They are much better when Q of capacitor is increased.

>>does paralleling capacitors increase or lower the Q?

Paralleling the capacitors will result in increase of Q.

>>what does “touchy”mean when talking about values between 82 and 100pF?

If you will notice as mentioned by others for a change of just about 18pF in capacitor value bandwidth changes almost by a factor of 2. So touchy here refers to capacitor values being critical, a couple of pF change has a significant impact and if you had been using a trimmer to tune this filter then the adjustment would be very sensitive and critical or Touchy...

If making filters I would highly recommend reading and archiving this paper by Wes Hayward:

Rahul VU3WJM

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