Multi Channel GMRS Repeater

[n9mnu]

I have a repeater setup that can operate on any of the GMRS repeater frequencies. Using a duplexer configured to operate on any of the frequency pairs works fine.

My goal is to be able to deploy the setup in the field, should it be needed, and allow a frequency to be set on-site using a single antenna.

What is the best way, or is it possible, to have a filter that will allow us to set the repeater frequency at deployment using a single feed line and antenna?

Two feed-lines and antennas I do not think are an option due to the vertical/horizontal separation required for proper attenuation. I thought about a high-pass filter installed on the receiver, a low-pass filter on the transmitter.

Any guidance will be appreciated.

 

[WA0CBW]

A duplexer allows you to use a single antenna along with providing enough isolation between the transmitter and receiver to prevent de-sense. Duplexers are basically tuned for a single transmit and single receive frequency. Trying to use them on frequencies for which they are not tuned is a bad idea. If you don't mind a little de-sense and a high SWR between the transmitter and duplexer then go ahead. Otherwise the duplexer should be tuned to the specific frequency you are using.
Bill

 

[prcguy]

The typical notch only mobile duplexers can be tuned to pass most if not all the GMRS repeater pairs and most duplexers would allow you to cover at least a couple of channels without retuning. I've carefully tuned a mobile duplexer to do this and had a channelized low power repeater that would cover all the GMRS pairs in the past.

 

[WA0CBW]

PRCguy is correct. Our shop has done just that but the results did not satisfy the customer as they wanted to run full power with less than clean transmitters and couldn't achieve a 60 mile range. As prcguy said using a clean transmitter and low power might meet your expectations.
BB

 

[kayn1n32008]

The typical notch only mobile duplexers can be tuned to pass most if not all the GMRS repeater pairs and most duplexers would allow you to cover at least a couple of channels without retuning. I've carefully tuned a mobile duplexer to do this and had a channelized low power repeater that would cover all the GMRS pairs in the past.

There is 0.175MHz from the lowest repeater channel centre to the highest repeater channel centre.

Using a Sinclair Q3330E you should be able to flatten out the notches enough to be able to pass all 8 repeater pairs and have 85dB minimum isolation. Passing all 8 GMRS repeater pairs should be easily achievable using a Sinclair MR-356 movile duplexer with out experiencing desense.

 

[n9mnu]

Thanks to everyone who responded.

I will check into the MR-356, which seems like a nice solution to a portable operation. The power output is only 20 watts on each pair. If we have to, having the duplexer work on a few pairs may be sufficient.