[Lowfer] coil, ERP, loop

[John Davis]

> Maybe loops are the way to go. I just ran a
>simulation of a one-turn 1.7 MHz loop made of 1 inch copper. 2 meters by 3
>meters and the efficiency is 3%.

Loops can be very effective, but there are big concerns about legality which
the individual operator must address to his own satisfaction.  (I'm obliged
to point this out, despite the risk of flames accusing me of saying things
I'm not actually saying, or side discussions about who's running excess
power, etc.  Just relax.  I'm not here preaching morality.  I'm simply
talking about what the Rules say and the practicalities of antenna
performance.)

Remember, the imaginary-cylinder concept is an individual interpretation and
has never been adopted by the FCC.  They were formally asked to do so, in
fact, but declined.  The Part 15 Rules simply say "length"--in common
English usage, the measure from one end of a thing to the other end.

The current-carrying path from one terminal of a 2X3 meter loop to the other
is 10 meters.  If one makes the perimeter a strictly legal 3 meters, with
each side 0.75m, the radiation at MF becomes pretty lame--far inferior to a
3m vertical out in the open.

Loop experimenters have clearly shown the advantages of a loop where height
alone is the limiting factor.  But if one takes "length" in its everyday
usage as the criterion, verticals still have the advantage.

When the LF ham band finally arrives in the U.S., I have no doubt that loops
will be the norm.  That's why the LWCA has been very eager to publish
research on practical experience with them, but with the caveat ahead of the
first article that you're on your own in establishing compliance with Part
15 Rules and Regulations.

John Davis