Subject: Indoor antennas for HF
From: Tim, N9RET
To: All
Date: 01/24/97

<This originated as a response to an inquiry about indoor antennas
posted on the AES BBS 01/04/97.  I have recreated it here for those
in similar "postage stamp" size lots who would like to experiment
with indoor wire antennas, and use some otherwise wasted space in
their homes>

As regards your indoor antenna- I am in a very similar situation, and
my solution was to construct what I call a "Spiral Dipole" in my attic.
The basic concept is this; starting at the center of the attic at floor
level, I hung two runs of 2-conductor wire from the roof joists, using
wood screw type standoffs designed for 300-ohm twinlead (available from
Radio Shack).  I spiraled each leg of the dipole up and in, using the
16" on-center joists to maintain consistent spacing.  When I reached the
end of the spiral, I soldered the two attached conductors together,
effectively doubling the length of each leg.  At the feedpoint, I used
only one of the two attached conductors from each leg, feeding the array
with 450-ohm twinlead ladder line to a tuner.  The other conductor from
eacl leg (closest to the feedpoint) is generally left floating, although
I have experimented with connecting the two floating ends together,
creating a loop-type antenna, with some success (apparent directional
characteristics, etc.).  This antenna tunes up from DC to Daylight very
nicely, and my first QRP contacts were well into South America.  It also
works well as a "Lowfer" reciever for the LW beacon band and (to some
extent) the MW broadcast band (although it tends to overload my reciever
at MW).  I have noticed some directional characteristics even when running
it as a dipole (ends left floating), but until I figure a way to rotate
the house,I'll just have to live with the pattern.
***Keep all the flammable junk that tends to collect in an attic well
away from any part of this set-up, and as an added measure, run as little
power as you can get away with.  I installed a smoke detector up in my
attic, just to be sure.  I have a small corner townhouse, and I was able
to make each leg of this antenna 115 feet long (twice that if you count the
doubling of the two-conductor wire at the end of each leg).  I am not sure
of the principals at work here, but the darn thing works- often better than
the ground-mounted 5-band vertical in my backyard!  If you have any further
questions about this array, drop me a letter and I'll include a pictoral
diagram of the antenna- it's neat, out of the way, and it works!
Good luck and happy DX'ing de N9RET<ar>