Duplexer Tuning Service In House Or On Site.
The Proper Way To Tune Duplexers.
I’ve seen people just set the separation by adjusting the tuning rod and notch. They get -80 to -90db of notch and call it good. Then they are having desense problems and can’t figure out why. You also have to tune the loops using a VSWR Bridge.. It’s a step by step process and if not done right you’ll likely have problems.
If they are tuned right you should only need four cans on a 2 meter repeater unless you have nearby repeaters causing you problems then you may need six cans.
I’ve also had people tell me they tune their cans with a watt meter. Good luck with that!
I’ve heard people saying it doesn’t matter if you tune the cans in reverse. Tuning the receive cans as the transmit, and the transmit cans as the receive. WRONG! The low pass coupling loops have a different capacitance than the high pass coupling loops. For example, the Telewave low pass loops have a 15pf capacitor and the high pass doesn’t.
Also the coupling loops have to be tuned with a VSWR Bridge to be dead on frequency. If the coupling loops are not tuned right the cans can still show that you have 80 to 90 DB of separation but they still will not work and totally mess up the receive.
80 DB of separation is fine if the coupling loops are tuned properly. You do not need 100 + of separation for them to work.
People will say the person they had tune their cans have been doing it for a long time and know what they are doing. I know Mechanics that have been turning wrenches for 25 plus years and still don’t know what they are doing!
Randy Savoix W1WRS