[BC] AM loop receiving antennas

[Glen Kippel]

On Fri, Jul 17, 2009 at 10:24 AM, Jim Wood, C.P.E.W. <
electrojim at sbcglobal.net> wrote:

> I came across this AM antenna from Ramsey Electronics, "Purveyors to the
> Pirates."
>
> http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SM100
> It's purported to be a Faraday-shielded loop that can be tuned from the
> 'studio' end.
> No idea if it would work in any of the applications cited, but it's only
> $90 in kit form.
> No way we could make it for that price!
>
-------------

OK, the Ramsey kit looks interesting, but I wonder about the varactor part
of it, possibly limiting its dynamic range.  Now, I have been using loop
antennas since 1960, when I moved into an apartment and couldn't put up a
longwire for MW DXing.  My first loop was a shielded, untuned Floppy Loop
made of mic cable and hung over a door so I could rotate it.  With a
Hallicrafters SX-71 and a homebrew antenna tuner I pulled in lots of 1-kW
stations in Central America, Colombia, and Venezuela, from northeast
Colorado.  Later I got some bendable irrigation tubing, a tee, and some
RG-58 and made a Hula Loop of about 5 feet in diameter.

You will need to decide what kind of loop you need.  Loops are ferrite and
air core; tuned and untuned; shielded and unshielded, balanced and
unbalanced.  A Floppy Loop is the simplest to build; just get a length of
any kind of shilded cable -- RG-58, RG-8, RG-6QS, whatever.  Decide how big
you want it, cut that much cable, expose the center conductor on one end,
and make sure it does not touch the shield braid at that point.  Now, cut a
small chunk out of the vinyl jacket and insert the exposed end of the cable
so that it touches the shield braid at that point only.  When you lay it
out, it should look like the number "9".  If it's not the right size, cut
another notch in the jacket.  Now hang it up somewhere.  Like over a drapery
rod, over a few finishing nails driven in the wall, stick it on the wall
with duct tape, whatever.  Connect the other end to the receiver input as
usual.  I have made these to go around the wall of an 8-foot-high by 10-foot
wide room.  Capture area is what it takes; the smaller they are, the less
signal pickup.

There is an article on a more elaborate Hula Loop at
http://www.hard-core-dx.com  Or you can get plans for tuned Sanserino loops
and others from the National Radio Club, International Radio Club of America
and other sources.  There are plans to make tuned loops out of ribbon cable,
too, instead of building a wooden frame and winding wire around it.

Commerically-manufactured loops are also out there, like the Kiwa and
Wellbrook designs that are quite good, but pricey.  The Select-A-Tenna has
been around for decades, and Universal Radio has them for something like
$60.  C.Crane doesn't seem to stock them any more.  I have a little Terk
AM-1000 Advantage, which is tuneable, non-shielded, small, and fairly
attractive.  Crutchfield wants the MSRP of $49.95, but most dealers like
Universal Radio, Solid Signal and RadioShack want $39.95.  I got mine from
B&H, where they now are asking $34.95.  See:
http://www.bhphotovideo.com/c/product/314639-REG/Terk_Technologies_ADVANTAGE_AM_1000_AM_ADVANTAGE_Indoor.html