Antenna system

All content is Copyright of The Bristol 70cms Repeater Group

The Antenna and Feeder system as used on GB3BS and GB7BS

The antenna system consists of a single commercial grade antenna of the CDF-450 series.

The antenna is made up from an array of 4 half-wave dipoles which are mounted at 90° to each other along a 2.5 metre pole and fed in phase by a special phasing harness and is the primary antenna for both GB3BS and GB7BS.

This configuration gives a good even 360° "H"-plane pattern. Each of the 4 dipoles can be individually moved (if required) to produce a custom "H"-plane pattern. The antenna configuration we are using has a gain of around 5.5dBd with an "E"-plane beamwidth of ± 8°.

The antenna is mounted at the very top of the tower which is at 30 metres. This configuration gives an un-obstructed 360° view and is void of any tower distortion.

Additional weather proofing has been applied to our new antenna prior to installation. This has proved to be very effective at prolonging antenna life and was trialed on our original antennas as used at Cossham Hospital.

          Antenna and Feeder Technical Summary:

  • 4 phased array half-wave dipoles.

  • Commercial Grade CDF-450 Series.

  • ± 8° "E"-plane beam width.

  • Symmetrical 360° "H"-plane (within ±1db).

  • Approx Gain 5.5dBd.

  • 0.8db Total system feeder loss.

  • Lightening Protection by way of DC short at Antenna Feed points. (Additional protection added using a 1/4 wave shorted stub).

  • Main Feeder type: CELLFLEX LCF78-50JA-A1.

Cross section of the Cellflex Feeder.