Re: Magnetic loop receiving antennas and electrical interference

In message <4a7b56f9$0$2487$db0fefd9@xxxxxxxxxxxxxx>, Robin <me@xxxxxxxx> writes

"Ian Jackson" <ianREMOVETHISjackson@xxxxxxxxxxxxxxxxx> wrote in message news:YDttR3aSvxeKFwQa@xxxxxxxxxxxxxxxxxxxx
In message <MPG.24e519e8e1b87144989954@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Conor <conor@xxxxxxxxx> writes
In article <689614b2-3496-47e5-bc5d-
8affe08eb52e@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Wimpie says...

<snip>
Good luck with finding an antenna solution for the interference!

There are some excellent videos of magnetic loop antennas on Ebay.
Quite a few seem to be in use in blocks of flats where space is
limited.

What about delta loop?

Delta loops are usually large aerials and, as such, are likely to pick up a lot of interference. The much-smaller 'magnetic' loop can sometimes be located away from the worse of the interference. It is self-contained, with no earth-return or balance problems. Most of all, it is small enough to be rotated so that (hopefully) the interference can be nulled out without losing the wanted signal.
--


One of the main benefits of the magnetic loop, is the very high Q, so narrow bandwidth, this significantly reduces the amount of crud that the RX has to deal with,

True, but you're talking here about the effects of receiver intermodulation - although I'm not sure that general background wideband electrical noise is usually sufficient to cause undue intermodulation, which it's usually the presence of exceptionally strong radio transmissions. If intermodulation IS a problem, on the lower frequency bands (where local electrical noise is normally worst), you can usually get rid of any intermodulation effects by backing off the RF gain or switching in some input attenuation.

another thing that may help you reduce local noise would be one of the devices that adds a second, short antenna in antiphase, this picks up the local noise and is then fed 180 degrees out of phase to the signal from your main antenna, the result is a reduction in noise as long as the short pick up does not pick up much from the TX that you are trying to listen to.

I've actually got one of these (rally stall) but, apart from a quick try, have never put it into service. Used correctly, I believe that they can work wonders. The problem is placing the noise aerial in a place where it tends to pick up more noise than signal.

In my location, most of my noise comes from a line of fearsome 400,000kV lines, about 1/4 mile away. Physically, it will be a very broad source of interference. If it's raining hard, the hash is S9 +40dB on 160m, dropping by about 20dB per band as you go up in frequency. When it's dry, the noise is there (although weaker). Any noise aerial simply tends to pick up a weaker version of what the main aerial picks up. I am seriously thinking that a separate receive-only loop aerial might be a better answer.
--
Ian
.

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