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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
Subject: [Milsurplus] AN/PRC-74 offset - clarifier
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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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