[MRCA] AN/PRC-74 offset - clarifier

[Mike Feher]

Ray - Not that it will be of any real help, but if you can find a RPST for
it, it may tell you what was at the depot. 73 - Mike 

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

 

From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> On Behalf
Of Ray Fantini via MRCA
Sent: Monday, October 6, 2025 2:15 PM
To: mrca at mailman.qth.net; milsurplus at mailman.qth.net; MMRCG at groups.io
Subject: [MRCA] AN/PRC-74 offset - clarifier

 

Been doing a bunch of AN/PRC-74 radios lately. Have a flock of them on the
bench right now working on synthesizer alignment.

That radio has an internal calibrator that you push in and turn that zero
beats the radio to the nearest 10 kHz. The same knob is also a "clarifier"
for use in receive. The weird thing is the clarifier allows you to vary the
1 kHz osculator up and down in receiver to correct for differences in
receive frequency and when you switch over to transmit the clarifier offset
is removed and substituted with a preset offset. The result is that you can
make small corrections when receiving when you transmit the radio goes back
to a preset offset and not the same frequency that you may be on. This is
only a matter of cycles, or hundreds of cycles but somewhat an issue. 

Tony N3KCB turned me onto the idea of disconnecting wire number 1 on TB601
and when you do that the relay that switched the offset generated by the RIT
out is bypassed and the result is the same amount of offset you needed to be
on channel is there when you transmit. 

Think that's a great modification. Now if I can get this whole mess of the
spectrum generator and the calibration oscillator sorted and the multitude
of offset oscillators set things will be looking up. And why is it you have
to remove the entire synthesizer deck to remove the covers to do an
alignment in the first place? Maybe alignment at depo was done with the
entire assembly removed so it did not matter about having to remove it and
replace it without the covers and then remove it again to put them back in
place.

 

  

Ray F/KA3EKH

 



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