[Hammarlund] Xtal Frequency Question

[wf2u at starband.net]

Crystal filter nominal frequency is only that: nominal. Technical manuals
of several receiver models explicitly require in the alignment  procedure
to determine the ACTUAL resonant frequency of the crystal filter and align
the IF string to that frequency. The LO frequency then is aligned to allow
for the ACTUAL IF (crystal) frequency, to the correct dial frequency. It's
normal for a crystal to be off due to aging - also, you probably don't
know how much your crystal was off from 455.0 KHz when the receiver left
the factory...

I always follow this procedure when aligning receivers and differences of
1 to 1.5 KHz from the nominal IF frequency is not unusual.

73, Meir WF2U
Landrum, SC


> 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.
>
>
>
> K3PID
> Ron H.
>
>
>
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