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GB3FM - GB3FN - GB3FNM - GB3FRS - GB3FX - GB3SN
The GB3FNM Beacon
The group also hosts the GB3FNM microwave beacons on behalf of the UK Microwave Group.
One beacon is currently active: 5.760 920 GHz (ERP = +17dBW)
GB3FNM Beacon description
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The beacon nominally provides omni-directional coverage subject to variations in the
antenna pattern. The antenna is oriented to favour directions up-country
and towards the continent.
The beacon provides a useful resource for propagation monitoring and enables microwave operators to check their receiving equipment. The equipment consists of an indoor unit (IDU) which includes the power supplies, keyers, stable frequency references and intermediate frequency generation. The intermediate frequency for the 5.7 GHz beacon and power are supplied to the corresponding mast mounted Outdoor Unit (ODU) via coaxial cables. Since early 2010, the OCXO has been locked to the 5MHz reference used for the GB3FN and GB3FX repeaters, to give improved frequency stability. The beacon uses a slotted waveguide antenna which produces 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 5.7 GHz beacon 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. |