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.
Recommended products
6-Inch 6-Cavity VHF Duplexer (BPBR)
136-175 MHz, 300 W, > 85 dB Tx noise suppression, 1.8 dB IL @ 500 kHz separation. 4 BR + 2 BP cavities.
- Freq
- 136–175 MHz
- Power
- 3 W
- Isolation
- > 85 dB
8-Inch 6-Cavity VHF Duplexer (BPBR)
136-175 MHz, 350 W, > 85 dB suppression, 1.8 dB IL @ 500 kHz separation. Premium 8-inch chassis.
- Freq
- 136–175 MHz
- Power
- 35 W
- Isolation
- > 85 dB
6-Inch 6-Cavity VHF Duplexer (BR)
136-175 MHz, 350 W, 60 dB ±1 MHz @ 500 kHz separation, 2.0 dB IL @ 1 MHz. All-band-reject 6 cavity.
- Freq
- 136–175 MHz
- Power
- 35 W
- Isolation
- > 6 dB
3-Channel Cavity Combiner VHF (8-Inch)
3 channel VHF combiner, 136-175 MHz, > 75 dB Tx-Tx isolation, 3.0 dB IL @ 150 kHz, 150 W.
- Freq
- 136–175 MHz
- Power
- 15 W
- Isolation
- > 75 dB
Field-deployed for this problem
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