Radio System

All content is Copyright of The Bristol 70cms Repeater Group

Technical and RF Hardware Information for the GB3BS Repeater.

The GB3BS UHF Repeater comprises of several units that all come together in one rack.

The repeater is based on the Tait T800 Mk1. It is a highly  popular unit often found within the commercial PMR world.The main units (left to right) are the Receiver, Transmitter, Monitor Speaker, Alarm Monitor and the Power Supply Unit.

The rack and all the modules within it remain unmodified as this helps for quick replacing of modules should a fault develop. Within the rack (between the Tx & Rx modules) is also mounted the six cavity Diplexer. Although with the addition of GB7BS this is no longer the primary Diplexer.

Below the Tait T800 is the Mk1 Logic interface unit, which was designed and built by the repeater group.

This unit is the interface between the Tait transceiver and the Arcom RC-210 Repeater control logic and has several functions. (1) To interface the Tx and Rx audio so as to keep impedance and levels correct. (2) Provide correct switching and logic levels such as Tx on/off, Squelch, CTCSS encode / decode, 1750Hz tone detection and filtering. (3) Buffering of analogue and digital inputs / outputs of the RC-210. (4) Environmental monitoring and reporting such as PSU condition, fan control, temperature and transmitter Drop Dead prevention. (click on picture for larger image)

Transmitter and Receiver Performance Data.

  • Transmitter Output Power: 15 Watts, 11.8dbW (into Diplexer Tx port).
  • Feeder Type: CELLFLEX LCF78-50JA-A1. Feeder Losses: 0.8db.
  • Antenna Type: Commercial grade SA-400 series, Gain: 5.5dbd.
  • Receiver Sensitivity: -120.5db for 12db Sinad. (at Rx port).
  • Squelch Open: 0.2uV.
  • Squelch Close: 0.15uV.
  • Squelch Hysteresis: 3db.

  • Diplexer Losses: Tx port: 0.8db Rx port: 0.6db.
  • TX<>RX Port Isolation: >80db.

  • CTCSS Deviation: 400Hz.
  • CW ID Deviation: 1.5 KHz.
  • Speech Deviation: 2.0 KHz.
  • Peak Through Audio Deviation: 4.7 KHz.
  • Overall system distortion: 7.5%

  • 1750Hz Tone notch filter attenuation: >60dbr.

Antenna combining network for  GB3BS & GB7BS.