Thursday, 6 August 2015

Tape Measure Satellite Beam - UHF Build, Pt 2

Building the UHF section of this antenna has proved somewhat trickier than the VHF section. For a start, the holes through the boom are a bit more critical, and although ordered my new reamer hadn't yet arrived to widen the holes a little at a time, so I had to do that carefully with a round file.

Once all the elements were in place, apart from the driven element and its support member, and all the sections aligned, the 'plugs' were secured with a liberal dousing in glue. Several coats of this glue might be needed to allow it to fully penetrate and make the joints fully rigid. The mostly assembled antenna was left supported on my workmate for several days for the glue to cure

Whilst the UHF section was curing, I got on with tuning the VHF. The driven element sections were trimmed to bring the resonant point close to the middle of the 2m band, and then a Hairpin match added to adjust the feedpoint impedance. Its actually resonant close to the middle of the band, but the match around the FM simplex calling frequency 145.500MHz (S20) is very good and the picture below shows just what it is around the satellite frequencies

Im quite happy with that! The Hairpin came out as about a 5 inch length of wire. The 50ohm RG-58 feeder is wound for 6 turns around the boom to form an ugly balun. Eventually, I might change the M3 bolts to some that are a bit shorter, as they are a bit too prominent and could catch on things during use.

Ive not yet tried the VHF beam on air. I'll test it at the weekend against several local repeaters.

The UHF section does now have its driven element in place, and is just awaiting connection of the feeder, and then testing and adjusting for the best match. I dont possess an analyser or SWR meter that works up to the required frequencies, so once complete I will take it to work and test it on the Anritsu Site Master testset in the service center.

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