Small TX loops are a moderately unexplored section of the radio universe
by hams. Impedances are very low, hence very high currents, I^2 * R
suggests small resistances really count.
I sold my Buddipole, which I've used in many field and SOTA excursions
and got an AlexLoop. Much lighter, sets up in 1/10th the time, QSY's
almost instantly, doesn't need elevation, 1/10th the weight or less, and
seems to be more or less equivalent to anything I could do with the
Buddipole. And, it's pretty much insensitive to "ground."
In the field, it is generally on a tripod over my left shoulder so I can
just reach up and tune it. K2, 5W, no tuning drift, and I don't line my
hat with tinfoil. Not sure I'd sit that close running power into a loop
designed for 100+ watts however. A good friend and retired EE pointed
out recently, "All the magnetic lines of force from everywhere in the
universe where I'm heard, go through that small loop." :-))
I tried just about every BuddiPole configuration and came to two
conclusions:
1. It doesn't matter how you extend the ends of the elements ... up,
down, one up-one down, in a "Y'. If the sections close in to the feed
point are horizontal, it's a horizontal antenna and elevation matters.
I guess I knew that from theory but it's nice when you see theory in
practice.
2. Any vertical configuration that includes some form of reasonably
good ground plane [2+ radials?] will be less sensitive to elevation.
Without a good ground plane, it will behave like a dummy load [on which
you *can* make a few Q's :-)].
The BP is a good field antenna, very well made, very sturdy, and well
supported, with lots of options. The full version is probably more
"luggable" than "portable." I think I just got tired of lugging it as I
get older.
73 and a happy and peaceful New Year to all,
Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org
On 1/1/2013 2:19 PM, Ken G Kopp wrote:
Small transmitting loops by their very nature involve high levels of
current flow and this can/will cause "ordinary" variable caps to heat,
which results in tuning drift. Most home builders use vacuum caps
and relatively large copper pipe in their designs. Mechanical joints
(clamps, wiping contacts, etc.) are to be avoided.
This tuning drift problem plagued the AEA loops of some years ago.
(I had the prototype here for early testing.) Does anyone know how
well MFJ's loop performs in this respect?
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