June 2008

On Saturday 14 June, major work was carried out to the tower and antenna system.  A lot of grateful thanks is due to Mark and Paul for spending the day changing out rusty bolts and strengthening the tower, and for fixing two new antennas.

The top antenna, which was a tri band colinear which went faulty in 2006 has now been replaced with a new Jaybeam colinear.  It uses the existing LDF4-50 feeder, which was in good condition.   GB3FN is currently running using this antenna, with single antenna working (TX and RX together use the antenna).  Signals are up by about 1.5dB to the North, a little more to the East as the side antenna which has been in use is shielded slightly by the tower in this direction.  The combination of the top antenna and the replaced bolts should reduce the rusty bolt effect that we have suffered in windy weather.

A new Alford Slot has been installed for GB3FM near the top of the tower, around 20m high.  This is on the East side.  The antenna is fed with a new run of LDF5-50, except for the last 20 feet or so to bring the feeder into the blockhouse, where an LDF4-50 extension is used.   The existing Alford slot is lower on the tower, at about 15m height, and faces North, so there will be differences in polar radiation pattern.  GB3FM is now running single antenna working into the new antenna.  Signals are up by about 4dB to the North.

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We now need a volunteer good with heights, wire brushes and paint brushes to repaint the tower, as the top section is quite rusty.