UHF REPEATERS

What most likely happened is that the signal from the radio caused enough interference to the signal from the repeater (even though they are 750 kHz apart) to stop it picking up the repeaters signal. If the radios had been further away then there wouldn't have been a problem. It comes down to the selectivity of the radio's receiver circuit.

Just out of curiosity what brand were the radios?

Firstly - there is no reason to use duplex if you are close.
Then it might depend on what channel you were on. CH 1 - 9(transmitt) & 31 - 39 (recieve) are the available duplex channels. Otherwise it sounds like you may have some other technical problem ??

I suspected you were using Uniden radios. I once tried a similar test with a Kenwood handheld and a GME in-car radio and I could hear the repeater on both radios, but they both have good selectivity in their receiving circuits, and very clean TX circuits.

As CJ said, you would normally not use a repeater when that close anyway, so isn't normally a problem, but it's good to be aware of the limitations of your radio... for example if you are receiving on a simplex channel, and someone close by is tramsmitting on a different channel, then you may not hear the incoming signal on your channel.

This gets worse with higher gain antennas. I used to have a Uniden radio at home with a 12 dB antenna, but found I got too much interference from the guy down the road with two phased 17 element yagis. So I sold that radio and got a GME and no problems now.

You guys have all missed the esiest explaination to the problem of accessing the repeater. If both radios are on the same channel as the repeater that they can hear the repeater, and both radios are on the duplex mode yet cannot get a repeater response then the simple explaination is that both redios are out of transmission range to the repeater. Repeaters are usually positioned on a hill, mountain or other high point so they transmit as well as they possibly can. If the radios that are being used are not in a similar position and are at some distance from the repeater it is possible to recieve the repeater and not reach it with the radios transmit signal. Handhelds are well known to suffer from transmit problems due to their lower power output and poor quality antennas. If the in-car radio has a bad antenna circuit or SWR then its performance will be compromised. Also some radios may not be able to communicate with each other if they are really close but this will be unrelated to the repeater access. Both my Uniden handheld radios can communicate with each other when in the same room. Andy

Thanks guys.

Andy, I think I follow your explaination, and this is what I thought may have been the problem.

Things were fine when on simplex (CH 3) but as soon as one of them was on duplex could not get through to the other set.

And yes the repeater was probably a bit far away.

Ta.

Russ