[Milsurplus] Milsurplus Digest, Vol 258, Issue 19

[Mike Christie]

 RayLooks like you got you work cut out for you. Please keep me in mind after you get some workingMikeW1ZFB
    On Monday, October 6, 2025 at 02:15:08 PM EDT, milsurplus-request at mailman.qth.net <milsurplus-request at mailman.qth.net> wrote:   

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Today's Topics:

  1. AN/PRC-74 offset - clarifier (Ray Fantini)


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Message: 1
Date: Mon, 6 Oct 2025 18:14:33 +0000
From: Ray Fantini <RAFANTINI at salisbury.edu>
To: "mrca at mailman.qth.net" <mrca at mailman.qth.net>,
    "milsurplus at mailman.qth.net" <milsurplus at mailman.qth.net>,
    "MMRCG at groups.io" <MMRCG at groups.io>
Subject: [Milsurplus] AN/PRC-74 offset - clarifier
Message-ID:
    <DM8P220MB047249F5B6E9F77B17C091C2B8E3A at DM8P220MB0472.NAMP220.PROD.OUTLOOK.COM>
    
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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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End of Milsurplus Digest, Vol 258, Issue 19
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