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eHam Forums => SWL (Shortwave Listening) => Topic started by: N5RWJ on November 19, 2011, 01:16:51 PM



Title: Magnetic Loops?
Post by: N5RWJ on November 19, 2011, 01:16:51 PM
Any commits?


Title: RE: Magnetic Loops?
Post by: HS0ZIB on November 20, 2011, 05:11:44 AM
I've used a Wellbrook loop for many years - excellent antenna for medium wave and top band reception

Simon


Title: RE: Magnetic Loops?
Post by: W8JI on November 20, 2011, 07:54:29 AM
Yes. Most are round, and signals are not magnetic.


Title: RE: Magnetic Loops?
Post by: WB6BYU on November 20, 2011, 07:06:33 PM
Why should anyone be committed?


If you can get past the misnomer "magnetic loop", there are several types of loop
antennas that work well for reception.  Because efficiency isn't as much of a problem
for receiving as it is for transmitting (as long as the external noise level is still the
limiting factor) then construction is much simpler, and there is no reason not to use
multiple turns for the loop.  I regularly use 4-turn loops for 80m that are 6 - 10 inches
in diameter and give reasonable performance over a 100kHz range (though with a
noticeable drop-off in signal strength at the edges.)

As you go higher in frequency you need fewer turns with wider spacing between
them to keep the self-resonant of the loop above your listening frequency.  I have
a 3-turn loop that tunes about 5 to 15 MHz with a mica trimmer.  Above that a
single turn loop such as this may be a better choice:

http://www.qsl.net/7n3wvm/mag-loop.html


Loops typically don't work as well in a building or near power lines - they still pick up
signals, but often more via coupling to the wiring than on their own, which tends to
pick up more electrical noise.  A remote loop some distance from the house, possibly
with a preamp and mounted on some sort of rotator, can give you the ability to null
out some noise sources.

There is also an untuned, preamplified loop design that I've seen, but haven't tried.


Title: RE: Magnetic Loops?
Post by: KE5JPP on November 21, 2011, 06:06:31 AM
Yes. Most are round, and signals are not magnetic.

LOL, this is very true!

Gene


Title: RE: Magnetic Loops?
Post by: KB9KXH on December 08, 2011, 10:49:14 AM
I use a wellbrook 1530 loop with the dc block replaced with a modified rf systems dx one control box which contains broadcast band filters and a switchable attenuator along with a rf systems wa50 rf amplifier which will add 10 Decibels when i switch it in. The dx one control box is a 220 volt version i found on ebay and i removed the power supply and used a metered variable power supply so i could monitor the current and voltage while having more filtering. I feel its about as good as i will get for an indoor antenna, I have no tower up here since i moved about two years ago but will have in the future.