On Saturday 18th August, a working party of five Committee members managed to fit a day in at the repeater site between contests, holidays and bad weekend weather.
The priority was the replacement of the Diamond X50 antennas previously used on GB3HS with a pair of commercial grade Amphenol J-Beam folded dipoles. The spec. can be found here: http://www.amphenolantennasolutions.co.uk/7050135-omni-center-fed-dipole-vh-pol-135-160-mhz-39-p.asp The X50s are not ideal for a repeater on a hill as reference to their radiation plots show that the main lobe is around 5 deg above horizontal. This is not helpful as most of the areas we need to cover are at sea level or not much above and therefore are below horizontal. The folded dipoles have the classic doughnut radiation pattern so they squirt RF in virtually all directions.
The main problem with the X50s is that they are made from mechanically jointed dissimilar metals. This causes noise to be generated in the TX antenna, when it has RF applied, which is then picked up on the RX when the antennas are flexed in the wind. We know that there will still be crackles caused by the tower in windy conditions but we hope that overall there will be an improvement.
We also took the opporutnity to align the new TX and RX antennas to maximise the isolation bewteen them and that has resulted in abolutely no desensitisation of the RX when the TX is on.
We also cleared out a lot of redundant hardware and equipment from the hut to make way for some new shelving. The shelving will hold new filters for GB7HU and a 2.2kVA UPS. The site was sprayed with SBK to kill off the weeds that seem to have attempted a takeover.
Thank you to all that gave up their Saturday.