[Elecraft] Magnetic Loops

[d.cutter at ntlworld.com]

I went to one of those lectures by Prof Mike Underhill (G3L??) in front of his IEE peers who did not receive his wisdom too readily.  It seemed like a one-man campaign.  In essence he postulated that a mag loop was more like a short folded dipole and he showed why.  The usual calculated losses were insufficient to show why loops worked the way they did.

I once made a loop from 12ft x 4ft sheet aluminium with a huge capacitor 4ft x 6inch vanes spot welded to the ends (that was an education in itself).  It was incredibly impractical, but I did it anyway.  I measured a 46dB front to side attenuation.  I scrapped it soon afterward.

David
G3UNA

---- Ron D'Eau Claire <ron at cobi.biz> wrote: 
> Clearly there's a lot of interest in small transmitting loop antennas, so
> here are some links I've collected over the past several years that are
> still good detailing the efforts of several Hams (I checked them to make
> sure they still work ;-):
> 
> Harry, SM0VPO, has several interesting designs including one built on a
> "packing crate" about which he wrote:
> 
> " I have been placed in a situation where a landlord denied permission to
> erect an antenna. Any form of antenna was unreasonable, even a white-painted
> broom handle caused interference!! My dartboard frame did not cause any
> interference at all..." and so he evolved his novel and stealthy small loop
> transmitting antenna. 
> 
> He also describes an 80 meter frame antenna. At the site below, click on
> "Projects", then "Antennas" and then look at links under Antennas on the
> left side of the page for "80 meter frame ant" and "Packing crate ant". 
> 
> http://web.telia.com/~u85920178/
> 
> --------------------------------------------------
> 
> David, PA3HBB/G0BZF has this nice page detailing his work with loops at:
> 
> http://www.qsl.net/pa3hbb/magloop2.htm
> 
> At the time he wrote the page he traveled a great deal and writes, " In
> order to fill my evenings with something other than foreign television (or
> drinking in the bar), I prefer to sit in my room and work the DX on the
> radio. Though this situation may not be typical of all of radio amateurs,
> the need for a small, effective and portable antenna will surely hit home
> with a number of them." 
> 
> ---------------------------
> 
> As a sign of the interest small transmitting loops generate, one fellow in
> Belgium created a very nice page detailing his loops and the work of others
> that ended up swamping him with e-mails, so it was relocated under a new
> URL:
> 
> http://www.qsl.net/mnqrp/Loop/Mag_Loops.htm
> 
> It details making loops as well as ideas for making your own low-loss
> capacitors to tune them with. 
> 
> -------------------------------
> 
> DJ3TZ built a small loop using copper tubing shown here:
> 
> http://www.qsl.net/dj3tz/loop2.html 
> 
> It has a nice fairly self-explanatory photo but most of the links on that
> page to other pages are now out of date.
> 
> --------------------------------------
> 
> 
> 73,
> 
> Ron AC7AC
>