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Old 22nd Jun 2017, 2:40 pm   #90
Andrew2
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Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Quote:
Originally Posted by merlinmaxwell View Post
Regarding orientation, if I where using a loop for local reception i.e. nonnulled rare stuff I would build two of these and put them at 90 degrees. It would work out much cheaper than my Welbrook and rotator and it (the array) could be rotated electrically, two pots and a bit of ingenuity.

Hindsight, a wonderful thing. Another thought, pot rotation would be instantaneous rather than the lag caused by the rotator (mine takes a second or so for 180, even then it is hard to get a null easily).
I've been experimenting with crossed loops on and off (mainly off) for quite a while. My main aerial is a Wellbrook loop which is excellent at getting rid of 80-90% of the local noise, but there are a few annoying ones that it cannot reduce or null.
A while ago I built a 'phaser-outer' and fed it with noise from a simple active whip which was roughly co-sited with the loop. Again, this worked on some noises, but with others it seemed to be receiving a completely different noise than that from the loop, so obviously no cancellation was possible no matter how I threw reversal switches and twirled knobs. There is one noise (a sharp buzzing sound that I suspect is a plasma TV) that is particularly stubborn.

So I've made a loop to the simple 2-transistor design that crops up in the magazines (very similar the PA1M one) and mounted it on the same stub mast as the Wellbrook, of course at right angles. This feeds the same phasing unit as before.
At last I can cancel the wretched plasma noise! I've also modified the phaser for a selectable second noise input from a basic 'bit of wire' antenna, and this works well on some interferences that the noise loop can't hear!
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