Tuesday, 11 August 2015

Tape Measure Satellite Beam - UHF Build, Tested

A big problem I have when it comes to testing UHF antennas is that my analyzer only works up to 170MHz. This means that transmitting on UHF into a homebrew antenna is a bit risky! And its a risk I didnt wish to take with the tape measure antenna.

Luckily, I have a friendly engineer colleague, and he has an Anritsu Site Master test set. This machine will do what my spectrum analyser, antenna analyser, VSWR meters and more do, but from 25MHz to 4GHz! And today over my lunch break I put the UHF beam on it.

Despite the fact that I have inadvertently cut the driven element too short, because I forgot I had marked the whole inches but not yet the tenths, and then went and cut it, the Anritsu showed that the resonant point was only a little high, around 441MHz. The part of the 70cm band used for the FM satellite downlink (Mode J) is around 436MHz, and here the VSWR was still well below 1.5:1. Perfectly usable. And this reinforces the on-air reception test a couple of days ago where I could still copy French and Spanish stations working the SO-50 bird down almost to the horizon.

All thats left now is to decide on a mounting method to join the two beams together for use, and to try the combination live against a satellite pass.

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