Solution

Eliminating RF interference between co-located VHF radios

Two or more VHF transmitters and receivers operating from the same site or tower interfere with each other through desense, intermodulation, and adjacent-channel leakage.

What is happening

When multiple VHF radios share a site, the receiver of one system sees a strong out-of-band carrier from a nearby transmitter. Even at hundreds of kHz separation, the receiver front-end is desensed — the noise floor lifts, range collapses, and weak signals disappear into the noise.

Why standard antennas do not solve it

Vertical separation buys only 20-30 dB even with several meters of mast. Tx-Rx splits below 1 MHz routinely demand 70-80 dB of rejection. The arithmetic does not close without filtering.

How a duplexer solves it

A cavity duplexer presents a sharp bandpass to your own carrier and a sharp band-stop notch at the carrier you must reject. With six high-Q cavities tuned correctly, you achieve > 85 dB of Tx-Rx isolation in a chassis the size of two thick books.

Recommended product family

For 136-175 MHz repeaters with Tx-Rx splits between 500 kHz and a few MHz, deploy the 6-Inch 6-Cavity VHF Duplexer (BPBR) (6-inch BPBR flagship). For tighter splits or higher power, step up to 8-Inch 6-Cavity VHF Duplexer (BPBR) (8-inch). For wider separations and 350 W operation, 6-Inch 6-Cavity VHF Duplexer (BR) (all-BR variant) is the preferred build.