AB7CQ & N7RPT

email: ab7cq@ebidpal.com

Tombstone, AZ 85638

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Yaesu DR-2X Repeaters & Henry Radio AMP Powered

Duplexer Tuning

If you're in need of repeater duplexer tuning services I can help you out. I'm a retired engineer and one of my hobbies is that of an amateur radio operator, I've been an active ham for 43 years and hold an Extra Class amateur radio license.

I own the necessary quality equipment to tune repeater duplexers, both bench type spectrum and vector network analyzers (VNA), "NOT NANO TOYS."

You need bench type analyzers that have the depth to peform an accurate and precise tunning of duplexers.

First piece of advise if you considering setting up a repeater:

DO NOT PURCHASE AND USE A CHEAP CHINESE NOTCH DUPLEXER.

The purpose of a regular (notch) compact duplexer, is to prevent the transmitted signal (RF energy) from entering the receiver and any received signal from entering the transmitter. It does this by notching out the transmit signal on the port of the duplexer that goes to the receiver, and by notching out the receive signal on the port that goes to the transmitter. The duplexer does not filter any other frequencies - only these two and only on the respective port. This means that a notch duplexer is only really suitable to be used on repeater sites that have no other repeaters on it.

Cheap Chinese notch duplexers will not work on a VHF repeater, they have a minimum seperation of 3.5 Mhz between transmit and recieve. This type of duplexer will definetly not work on a site with multiple repeaters. A notch duplexer will not prevent an unwanted signal from entering either the receiver or transmitter.

The unwanted signal could come from the transmitter of another repeater on the site. Any RF entering your repeaters transmitter, can generate harmonics (i.e. other repeaters transmitter frequency multiplied or divided by 2;3;5;7 and 9). These harmonics can mix with your repeaters transmitter signal - or the harmonics thereof - and produce intermodulation products. These products can in turn, mix with each other producing an inordinate number of products, in a worst case scenario.
 

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