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Duplexer For A Repeater With 1mhz Bandwidth

Duplexer For A Repeater With 1MHz Bandwidth In The VHF 136-174MHz Range

In radio communications, a is used in repeaters to allow for simultaneous transmission and reception of signals without interference between the two. In the VHF 136-174MHz range, such duplexers play a crucial role, especially when dealing with narrow bandwidths like 1MHz.

VHF P25 Repeater

When you have a operating within the VHF 136-174MHz range, it's crucial to ensure that the transmit and receive frequencies don't interfere with one another. Let's say you are using a split where the transmit frequency is 1MHz above the receive frequency. In this case, the duplexer will:

  • Use the band-pass filter to allow the repeater's receiver to hear incoming signals on its designated frequency, while blocking out the transmit frequency.
  • Use the band-reject filter to prevent the repeater's transmitted signals from interfering with its own receiver.
VHF P25 Repeater

Tuning 146.475 VHF Band-pass/band-reject Duplexer

Band-pass/band-reject Duplexer Application For Vhf 136-174mhz Bandwith 1mhz Repeater, This type of duplexer uses both band-pass and band-reject filters. The band-pass filter allows only the desired frequency range to pass through (in this case, a specific 1MHz bandwidth). At the same time, the band-reject filter prevents unwanted frequencies from interfering.

VHF 136-174 Duplexer

Repeater Access Information:

  • Frequency: 146.475 +1MHz
  • NAC: 555(hex)
  • PL: 100.0 / 100.0
  • Talkgroup can be configured to be 1 or 200.  As far as my testing has shown, the repeater will broadcast all traffic on between either group.

Equipment:

M/A-COM Mastr III Repeater

  1. Originally designed for 136-174 MHz Operation
  2. 110W PA
  3. M/A-COM DSP Module for P25 Operation
  4. VHF 136-174 MHz TXRX Systems Duplexer
  5. TXRX Systems Pre-Amp
  6. Comet GP6
  • The exact frequencies for the band-pass and band-reject filters will need to be set based on your repeater's operating frequencies. Proper tuning is crucial for optimal performance.

Why Duplexer Is It Necessary?

VHF UHF cavity duplexer

Without a well-tuned duplexer, the repeater's own transmissions could “desense” or effectively “deafen” its receiver, rendering the repeater useless. If you are operating a repeater within the VHF 136-174MHz range with a 1MHz bandwidth split between transmit and receive frequencies, a well-tuned band-pass/band-reject duplexer is essential to ensure effective and interference-free operation. When purchasing a duplexer for this purpose, ensure it is rated for the VHF range you're working in and is adjustable/tunable to your specific frequencies. If you need Filters & Duplexers & Coaxial Cable & Connectors & Antenna, maybe I can help you, We have been supplying continuously for 10 years.

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