[ARC5] VHF R-28 and BC-942 Crystals.

[David Stinson]

Concerning crystals for the BC-942 and R-28
"ARC-5" VHF receivers:
The manual calls-out  Fxtal =  Foper. - 6.9 MC / 24.

Example:      Fop 118.55 MC - 6.9 MC = 111.65
                          111.65 / 24 = 4652 KC  Fcrystal.

Please note that these multipliers will also work:
12, 18, 24 and 30.
So for the Unicom freq of 122.8 MC,  one could
use crystals:   9658, 6439, 4829, and 3863KC

Additional note:
If you use one of the inexpensive and very useful
DDS function generators like this one:
https://www.amazon.com/dp/B0759GKKBJ
one must use a square-wave output (high in harmonics,
as crystal oscillators are).  I use the CMOS waveform.
The receiver will operate well with 5V+ positive-going
square waves (CMOS setting), so programmable oscillators
with only DC blocking cap of 500 pFd will work OK,
but best sensitivity on my two working sets is at 10V+ peak.
Higher than 10 and sensitivity goes down.  Personally, if I
want .25 uV sensitivity, I have scanners for that.
I will trade some sensitivity for simplicity.  Still works well.

Hope this is helpful.

73 Dave AB5S


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