HFU HF Underground
Technical Topics => Equipment => Topic started by: ChrisSmolinski on July 28, 2018, 1754 UTC
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A brief update on this antenna. For reference, the original build article is here: http://www.radiohobbyist.org/blog/?p=2340
I finally poured a concrete footing with a piece of pipe in it, as a support for the rotor. Previously I just had the rotor mounted to a piece of plywood sitting on the ground, which as you can imagine was not exactly stable nor free from moving around.
This also led to me finally calibrate the rotor azimuth, using local MW and LW station as references, nulling them out an comparing the bearings to predicted, then adjusting the loop antenna to match. In the process of moving the antenna back and forth, I discovered the rotor controller has a thermal cutout switch! ;D
Now it is fairly closely calibrated, and I can more quickly null out known stations, and get reasonable estimates of the bearings of MW stations via the null. Switching to one of the beverages usually helps remove the 180 degree ambiguity.
I am impressed with how good the nulls are, usually 20 to 30 dB, sometimes more, on MW stations. The loop works well up into the HF bands, even to 10 meters, although there is no predictable directionality up there as you might expect. The antenna is made of four loops, each is 1 meter on a side, 4 meters total. It is somewhat directional for CHU 3330, but by the 41 meter band it does not seem to be directional at all.
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Put a goniometer in it!
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Sounds great, Chris.
A small loop without a rotator is like a radio without knobs.