You will get better results and probable answers at

rec.radio.amateur.antenna

Since GMRS frequencies are around 462 MHz -- see URL:
http://www.g-m-r-s.org/frequencies.htm

I would start by measuring the SWR and see how far off things are.

There are several ways to match the transmitter to the load

UHF Tuners, matching networks etc

Combiners allow the use of different bands - so don't think that will help

Again try rec.radio.amateur.antenna
The experts are there.

--
Caveat Lector



"Richard" wrote in message
...
I need help with a project.

I have a tower site where there is a existing UHF antenna 200 Ft on hard
line mounted and existing. (460.0 mhz)

Is there a device to retune the antenna to GMRS to go on the back of the
radio to retune the load?

Would a combiner help?