FARNHAM VHF GROUP
GB3FM - GB3FN - GB3FX
The group is hosting three microwave beacons on the site for the UK Microwave group. We can't take any credit, except for having a site which is a bit drier than being outside, and a tower (just). The beacons were built by G8ACE and G4NNS and project managed by G8KQW. All three have antenna systems that are located at approximately 15m above ground level.
The three beacons operate on the following frequencies and power levels:
5.760 920 GHz with ERP of +17dBW
The 5.7 and 24 GHz beacons are intended for area coverage. The 47GHz beacon is directional and is directed to the SSW.
The beacons are intended for propagation studies and as a resource for microwave operators to check their receiving equipment.
The complex consists of an indoor unit (IDU) which includes the power supplies keyers and Oven Controlled Crystal Oscillators (OCXOs) for each band. The base band frequencies along with power are supplied to the corresponding Outdoor Units (ODUs) via coaxial cables. Since early 2010, the OCXOs have been locked to the 5MHz referenced used for the GB3FN and GB3FX repeaters, to give improved frequency stability.
The 5.7GHz and 24GHz beacons use slotted waveguide antennae which produce a polar diagram in the form of a four leaf clover with approximately 10dB of gain in the main pair of lobes (180 degrees apart) and 6dB gain in the minor lobes (at right angles to the main lobes). The nulls are at approximately 0dB. The main lobes are aimed ENE/WSW while the minor lobes are at 90 degrees to these, i.e. NNW/SSE. The 5.7GHz antenna is housed in a separate Radome connected to the 5.7GHz ODU by a short length of low loss cable. The 24GHz antenna is housed in a radome which is an integral part of the 24GHz ODU. The 47GHz antenna is a horn located within the polycarbonate enclosure of the 47GHz ODU. This is directional and is pointed to the SSW.
The 5.7GHz beacon has been heard as far away as Belgium, Denmark and Sweden! The 24GHz beacon is regularly heard in Andover, Winchester and Danbury, Essex. Ian, G8KQW, would like to get as many reports as possible!
Updated May 2014
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