"Dave" wrote in
:

....
Hello Owen,

Sorry I am just now getting back to you on this, but I have been
reading and studying your article. I constructed a loop somewhat like
the one you discuss, but have one question: you speak of a "feed tee"
from which the feedline extends. Should I be able to buy such a
T-shaped device at my local parts outlet? I asked about such there
one time, and was practically laughed at. But it seems such would be
very handy for antenna builders of all types. If my local parts
distributer doesn't have this item, where can I get it and what should
I call it ("feed tee"?)

Dave, the 'feed tee' I refer to is the tee at the bottom of Fig 1. It is
not a standard component that you would buy off the shelf. I have used it
as a descriptive term, sorry if it has confused you. The important detail
is the electrical detail. In commercial loop constructions, the thing is
usually a box, the the loop coax enters opposite sides of the box with
effective circumfrential shielding. The box is a convenient mounting and
good location for an amplifier if used.


The loop I constructed is extremely primitive, but still functions
nearly as well as the 110' longwire antenna I have used for years.
And it is *directional*, though sometimes noisy (probably because the
feedline does *not* exit and travel symmetrically away from the loop,
I am guessing.)

I am not suggesting that loops aren't directional. Shielding a loop is
one (and only one of several) of maximising the pattern nulls.

Symmetry helps to ensure that the feedline is not effectively part of the
system radiator.

The noise issue may be related to the above.


The main way in which my loop differs from your design (other than the
feedline asymmetry) is the fact that the shield is not cut away from
the center conductor opposite the feed input. Can you tell me what
function this feature serves?

I don't understand just what you mean. Perhaps your construction is like
Fig 3 (from the ARRL Antenna Handbook), but as stated, it doesn't do what
they say it does. That is not to say it doesn't 'work', or that it isn't
directional. The stuff about shielding against electric and not magnetic
fields is a flawed explanation.

The real radiator is the outside of the outer conductor, the feedpoint is
the gap, and the construction is a clever way of achieving maximum
symmetry by placing the feedpoint at the top and routing the coax to the
feedpoint in a way that is symmetrical with respect to the outside of the
outer conductor of the loop. If you don't route the coax away from the
tee in a very symmetrical way, don't waste your time on the complicated
construction.

Owen