From: Steve Miller (firstname.lastname@example.org)
>At 13:58 5/28/97 -0800, you wrote:
>> Don't laugh out loud but:
>> When hand picking crystals for a filter network, can you do it by ear?
>> That is to say, can you plug them into an oscillator circuit and
>> listen on a receiver for the ones closest in tone? Or are you looking
>> for much more precision?
>> How close should they be to each other? What can I expect?
>> What if I just use four from the same batch? If they are off a little
>> how much will it affect the final result?
>> Tim, ka8ddz
Tim, you have to match frequency. Build a little oscillator test circuit.
Use a frequency counter and try to find four that are within a small range.
The rule of thumb is 10% of your filter bandwidth. So a 400 hz filter
would need 4 xtals within 40 hz. I bought 20 from Digikey (or Mouser ?)
last time and matched two sets - one within 10 hz and one within 20 hz.
The was another that was about 40 hz so my order of 20 was plenty. The
tighter the range the better. 73 and gl.
Steve Miller kg7pv @ teleport.com Portland, OR
(CN-85) Norcal #308 QRP-L #109 ARCI # 9230
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