your closet door as "super loop"
David Barts (email@example.com)
Date: March 16, 1995
Original source: Usenet's rec.radio.shortwave
Kinsler (firstname.lastname@example.org) wrote:
In accordance with instructions imperfectly recalled from
an ancient electronics magazine I once wound a sort of "super
loop" antenna around the periphery of a closet door. I don't
know how many turns of what kind of wire were supposed to be
used, but I did think it was cool that you could swing the door
so as to orient the loop properly.
This, plus a variable capacitor, should make a pretty good broadcast-band
antenna. Does anyone know the proper specifications, assuming
a non-ferrite closet door?
through the math last July, and it turns out that if you use a
square form and a standard 0-365 pF tuning capacitor, using about
80 feet (25 meters) of wire will do the trick (irrespective of
the size of the square you choose).
A closet door is of course not square, so the wire length will
be different (probably longer, but it's been a while since I worked
out the math and I can't exactly remember). You could always drill
holes in the door in a square pattern, insert wooden pegs, and
use those to wind the loop.
Take care to separate the turns of wire (1 cm or more between
adjacent turns is best) to minimize self-capacitance inside the
loop. If you don't, the extra unwanted capacitance will prevent
the antenna from resonating at the upper ends of its intended
There are also companies that sell pre-built loop antennas. However,
this is one area where you can save a LOT of money by building
your own. I've seen tuned loops that sell for $100 or more, and
I spent around $5 on mine.
BTW, the closet door idea is very clever! I may re-build my loop
in that way; currently the most awkward thing about it is rotating
and orienting it properly without it falling over.