Simplex Radios on Congested Repeater Sites

[Birken Vogt]

I'd like to know how all of you are accomplishing having simplex channels on a site with lots of repeaters.

My specific scenario is that usually we have a master receive antenna at the top with various filters and preamps teed into the line at the bottom which works well.

We have transmit combiners that do the same thing, usually 40' below the rx antenna.

If I want a simplex frequency up there, I pretty much have to hook the radio up as if it were a repeater and have dual filtration for it.

However, I am wondering about the effect of the transmitter blasting into the preamp or receiver right on frequency.

How much power can a receiver reliably handle without damage?

[Bill_G]

DON'T
DO
IT!
PLEASE.

If you must operate simplex, and you must use the site rcvr multicoupler and xmit combining system, and you don't have a radio with dual antenna ports like an MTR or a Quantar, then get a second radio to act as the receiver.

If you transmit up their master rx, you'll blow it up. If you try to receive down their master tx, they'll blow you up.

[Birken Vogt]

Of course use radios with dual antenna ports. I am not going to use a mobile radio at a commercial site. This is more of a general question. I am not a novice.

But with the transmitter and receiver on the same frequency, even though the antennas are separate, there is going to be a lot of jam coming down the rx antenna and rx cable because there is no filter skirt to be down on. It will come right in the rx filter.

I tried to make that clear in the original question. What is a typical level of strong signal power a rx can handle in a situation like this?

[Bill_G]

Okay. The medium doesn't help totally express ones intent. Thanks for clarifying.

The energy coming down the line could be considerable even if it's not your signal. Hence the multicoupler shelf. It will offer you all the protection you need. But! You will want to mute your rcvr during xmit, or at least mute the rx audio on your remote control so you don't set up an acoustic loop.

[Birken Vogt]

There is this one major site where we have several other customers and one thing I noticed recently was that the USFS had some kind of simplex operation in there at one time. They have a transmit combiner port on a particular frequency and a multicoupler port on that same frequency. Unfortunately for my curiosity there is no radio installed any more so the ports are just sitting there idle, so I can't see how they did it.

[motorola_otaku]

Vertical separation is going to be your saving grace here.

On the base station side I would keep the T/R relay in place on the receive side only, that way when the station keys it will continue to isolate the receiver during transmit.

[Birken Vogt]

The T/R relay was my thought also.

However, I am still curious what a reasonable figure for amount of strong signal a receiver can handle reliably.

[Bill_G]

It's a busy site. Measure what's coming out of the proposed port you will plugging your receiver into.

[Birken Vogt]

Is there a figure on how much signal coming in on-frequency is allowable in say a MTR2000 or similar?

[Bill_G]

Not really. Me personally I like to keep it below -40dbm at the input just to keep the preamp out of saturation.