[Hammarlund] Xtal Frequency Question

[James A. (Andy) Moorer]

Normally a crystal will be accurate to, say, 25 ppm. That would be .0025%

As noted elsewhere, surrounding circuit elements can shift the frequency. It 
generally can't shift the frequency by more than 100 ppm, or .01%. I built a 
VCXO once that could swing the frequency by 250ppm, but I had to get the 
crystals specially cut to get them to swing that much. A normal crystal 
won't swing more than .01% or so before it stops working.

James A. (Andy) Moorer
www.jamminpower.com


----- Original Message ----- 

I have determined that the 455 KHz HC-6 crystal that is used to form the 
filter in my HQ-145 is about 1 KHz low. That's about 1/455 or 0.2%.  I also 
noted that the marking is 455 kcs while I can purchase one marked 455.0 kcs. 
The extra decimal would imply another digit of accuracy.

QUESTION: Is that pretty typical? Since I can easily align the IF string to 
match the 454 KHz filter, and I can also adjust the LO to be in calibration, 
is there any significant downside to running with the 455 KHz IF a KHz low? 
Should I spring for the 455.0 Xtal? If I wanted to get real adventuresome, I 
could open it up and polish off a little which would raise the frequency. 
Haven't done that is 30 years and never with an HC-6 can.