[Elecraft] Good Low Horizontal Loops - questions

[Stuart Rohre]

LLoyd,
The distance across the feedline attachment point is not critical.  It is a
small fraction of a wavelength and you do not worry about such effects until
they are 0.01 wave length in size.

You feed the loop where convenient, corner, or side.  There will be some
influence on the omnidirectional pattern, but keep it symmetric if you can.

An ideal loop is a circle to equally radiate in all directions, but a square
will work fine, and triangle, and even a rectangle, until you get quite
close on two sides where the rectangle degenerates into a folded dipole.
You should try to keep an equal sided arrangement if possible, to work all
directions equally well.

A random wire that has too many bends and direction changes will have
cancellation of part of its radiation.  The loop cleans things up, allows
all directions to have gain, and is lower noise than an open ended wire or
even a dipole.  Signals you cannot hear on a dipole because of noise floor
will be heard and worked on a large loop.  It would be best to use a
balanced tuner, or a balun to feed the loop.  There is really very little
loss from our extensive club use of loops, thru many of the built in baluns
in transmatches commercially available.  But, it is easy at QRP to build a
balanced transmatch also.  You could use a balun on the built in tuner to
better keep the feeder balance using parallel line.  But, some have worked
out well just using the coax built in tuner output to feed a balanced line.
However, depending on line length, you could get RF problems from that.  If
the feeder radiates a little it might not hurt at QRP, since hopefully you
will route the feeder as clear of other conductors as possible.

The gain of a loop operating as 2 wavelengths or more on a band is VERY
worthwhile to have, and will give you a commanding signal on the high bands.

The double take off lobes are a great way to work all states and work DX
with the low angle lobe as well.  You are lucky to have all that room and
trees; a loop will allow you to make best use of it.
72, Stuart K5KVH

The impedance at the feed might be 100 ohms on some bands and something else
on other bands.  That is why you use a transmatch, as it does not matter;
you adjust it out.  Also, open wire line is very low loss compared to coax.
450 ohm is lower loss than 300, and that is lower loss than 50 ohm coax.
The higher the impedance, the less the loss.  An open wire or parallel
conductor feeder can operate with high SWR, without a penalty of the
mismatch magnitude you would have with coax with all its dielectric.

Thus, feed the loop with whatever you have.  The antenna is fully balanced,
as is a dipole.  One way to think of this is the "two sides" simply join at
the point opposite the feeder which will be a symmetric point.  Thus, as a
balanced antenna like the dipole, it does not need counterpoise or radials.
It is complete radiator unto itself.

The field around the parallel line tapers off in a few diameters.  As long
as you cross conductors at right angles, there will be minimal effect at
metal window sills for example.  Ever look at spacers at Radio Shack for 300
ohm line?  They are about 6 inches long, as that was sufficient spacing for
the VHF TV frequencies.  Similar spacing can be provided for HF feeders,
using electric fence standoffs which allow 450 line to snap into their
holders.  They are 5 to 6 inches long, made of black or yellow plastic.
Ranch and Farm Stores and some Home Depots carry them with electric fence
supplies.  Other spacers could be home made from PVC pipe.
The Wireman carries one type made from pipe.