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This is my first time ever asking a question on stack exchange or any stack site, so please be gentle if I missed something here.

I am currently working on building a UHF (GMRS) repeater, and while picking equipment and such, I got to thinking about whether a power amplifier is something that can be used with a repeater. I don't intend to run an amplifier, but was wondering if it is theoretically possible. I have done some web searching and haven't had a whole lot of luck finding the answer I am looking for. I was wondering if someone could confirm whether my theory is correct..

Consider the following, fairly basic, setup: Dual commercial radios connected to a properly tuned UHF cavity duplexer sharing a single antenna for both RX and TX. If I were to put an amplifier on this rig, I would need to place it on the transmit radio side of the duplexer, NOT on the antenna side, correct? I assume that, if placed on the antenna side, the moment the transmit radio keyed up, it would shut off any signals coming in to the receive radio effectively disabling the system to be used as a repeater at all.

In short, if you want to run a power amplifier with a repeater, you would potentially need two devices.. a pre-amp for the receive, and a power amp for the transmit, connected as follows:

RX <== Pre-Amp <===== |----------|
                      | Duplexer | <===> Antenna
TX ==> Power Amp ===> |----------|

(I hope the diagram makes sense lol)

Is my thinking on this correct?

73s, Steve

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    $\begingroup$ Hello Steve, and welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Oct 26, 2020 at 18:04

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Yes, your diagram makes sense.

And yes, it's doable, given that your amp operates within the power limits of the duplexer and the antenna, and the duplexer isolates the receiver from enough of the amplifier's output.

Every solid-state rig that outputs more than a watt has a power amp inside of it already, so it's not a question of "can it be done" but one of "how much?".

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    $\begingroup$ Right, I understand about the isolation provided by the duplexer. I guess to clarify my question, if using an external power amp, would it need to be located on the TX side of the duplexer as opposed to the antenna side with an optional separate external pre-amp on the receive side? Was I correct in that, if placed on the antenna side of the duplexer, it would cause the repeater not to function. Sorry, if this is a basic question.. I have 0 experience with external power amps, working off a theoretical understanding only. $\endgroup$
    – hairlesshobo
    Oct 26, 2020 at 15:46
  • $\begingroup$ @hairlesshobo yes, you got it right. $\endgroup$
    – hobbs - KC2G
    Oct 26, 2020 at 16:21
  • $\begingroup$ great, thank you for the clarification! $\endgroup$
    – hairlesshobo
    Oct 26, 2020 at 16:35
  • $\begingroup$ It also needs to stay within the 50 watt legal limit for GMRS. $\endgroup$
    – AI7OW
    Aug 28 at 17:00

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