Calibrating Heathkit IM(or SM)2420

[Mark Graalman WB8JKR]

  Hi Malcolm,

  I calibrated mine quite nicely at 15 Mhz against WWV, but two
simple mods have to be done to the counter first.
 The temperature control circuitry, namely transistor Q10
puts out a square wave and the harmonics from this circuit
emit so much noise, you can't calibrate the counter, this
is corrected by placing a .001 ufd 100 volt disc cap from
Q10's collector to ground.
 Then, tack a 100 pf 100 volt disc cap to U9 pin 15, this
will provide a 1 Mhz output signal tap off point to use to
beat against WWV at 5, 10, 15, or 20 Mhz.

Mark  WB8JKR


On Tue, 16 Dec 2003 08:01:57 -0500 Malcolm Leonard
<radiorepair at MINDSPRING.COM> writes:
> Can the above be calibrated without specialized,lab standard
> equipment?
> Thanks,
> Malcolm Leonard
>
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