Repeater

Pataman

Hi Guys, I am in trouble. I have just installed a new repeater system in work. I am using 2 motorola gm300's, duplexer, connecting lead(rick) and aerial.
I am getting terrible reception. When I use a handheld the receiving gm300 sometimes doesnt open, if I am about 300/400 yards away. I have a spare gm300 and it was the same as the others. I suspect 2 items could be at fault: The duplexer or the aerial.
Duplexer: this is over 10 years old, however it was retuned to my frequencies last week. Do they wear out?
Aerial: I was sold a marine aerial. The frequency range is probably156-160. The repeater receive frequency is 160.25 and tx 164.75. I suspect my swr is quite high. Considering I am txing 25w, do you think the swr is high enough to damage the tx radio?

Taildragon

I'm assuming you're using a cavity duplexer? Duplexers don't "wear out". They will suffer degraded performance from physical damage (distortion of the cavities) or corrosion of the internal silver plating.

Basic question: You do have it connected the right way around?

I wouldn't worry about the SWR at this stage, the (correctly installed, aligned) duplexer will mitigate the effects anyway.

Pataman

Yep the duplexer is wired correctly , high, low antenna. I am in the process of checking connectors, and am going to replace the rg58 with low loss coax to see what improvement it makes.

watty

The connection cable length Between cavities must be exact.
The cavities have to be adjusted for the exact TX & RX channel in use. A professional can tune them.
how do you know the cavities are tuned to your frequency?

Screening rather than loss is important.

Pataman

Thanks for your answer guys. I have replaced the cable and also all connections and it has made a difference, but still not as expected. However I was talking to the guy who tuned the duplexer and he says the separation between tx and rx was about 70db. He said it should be at least 80db. I was looking on ebay and they have load of new 6 cavity(I have 4 cavity) duplexers for around €50 + p&p.
Would it be worth a punt?

watty

I had to put an outer screen on the two gm300 radios feed coax (between radio and duplex cavities), earthed at one end only, insulate the radios from Chassis and put RF chokes on all cables (separately) (power, speaker, controller, mic etc) to get good TX/RX separation.

Pataman

Hi Watty. chokes - you mean the ferrite rings?
what sort of outer screen did you use?
The radios are sitting on a desk, so insulated from each other.

watty

one or two turns through clip on type

I used braid taken off RG213 and slid it over the existing cable with two tie-wraps, one on connector at one end as earth and other to hold braid on insulation just short of connector at other end. Earthed at cavity end I think.

I tested isolation by having a dummy load instead of aerial on the cavity via reasonable length coax and handheld at 100mW with small dummy load (50 Ohm BNC plug type) on the handheld. You should get about 200m to 300m range.

Pataman

Brill. I will give it a go
Thanks