[Elecraft] Good Low Horizontal Loops - questions

[k6se@juno.com]

Lloyd, K3ESE wrote:

"I could probably string a roughly circular 1K' loop on my lot, through
the trees, with an average height of about 50'. Here's what I need to
know, though; when feeding the loop, is the loop broken, with one side of
the feedline going to each side?  If so, is the distance across that gap
critical? What types of feedlines would work - which would be best?  Can
I use twinlead? Would I need a balun, an rf choke, or whatever?"
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A 1000-foot horizontal loop has its first resonant point far below any
amateur frequency, however it display resonant points (zero reactance)
about every 2 MHz, with the first one in an amateur band at the high end
of 160 meters where, if it is a closed loop, the resistive part of the
feedpoint impedance is about 100 ohms.  On that frquency you could feed
it with 50-ohm coax through a quarter-wave section of 75-ohm coax at the
feedpoint with close to 1:1 SWR on the 50-ohm line.

That however, would make it a single-band antenna, so the best way to
feed it would be as a closed loop with 450 to 600-ohm ladder line and use
the antenna tuner to match the impedance seen by the transmitter with
your "antenna" tuner.  This would make it an all-band antenna.

The best single-band square horizontal closed loop would be one that has
a total wire length of one wavelength.  This would be about 270 feet on
80 meters.  At resonance, this antenna also has a resistive part of the
impedance of 100 ohms, so it can also be fed easily in one of its corners
by 50-ohm coax via a quarter-wave 75-ohm matching section at the
feedpoint as described above.  You wouldn't need to use a tuner with this
antenna.
==========

"My rig is a K1 with KAT1, 40-30-20-15. Would one end of the feedline go
to the center conductor, and one to the ring?"
----------
Connect the ladder line to your K1's tuner as outlined in the manual.
==========

"Would I need counterpoises?"
----------
No, not with this antenna.
==========

"Will the feedline radiate?"
----------
The currents in the two sides of the balanced line are out of phase with
each other and cancel, so there should be no radiation from the line.
==========

"Is it ok if it does?"
----------
If it does, it means its balance is disrupted by one side of the line
being closer to an object (usually metallic) than the other side.  Just
take care how you run the line, especially where it enters the house.
==========

"I'm now using a longwire of about 200' that goes every which way, and
works very well - good reports all over Europe, down to Central America,
and domestically. Should I be satisfied with that, and cease this endless
restless quest for gain?"
----------
Never cease the quest for gain in an antenna, hi.  You never know how a
makeshift antenna will work until you try it.  Your 200' wire is an
all-band antenna, and the loop is a single-band affair (unless fed with
ladder line via a tuner).  Pick a band to build the loop for and see how
it compares with the 200' wire on that band.  If the loop outperforms the
wire on that band, then keep it.  If not, either feed it with ladder line
via your tuner and try it on the other bands or take it down and try
something else.

BTW, you have a *great* CW callsign.  If you can drop that first "E" from
your call we can become blood brothers <:o)
 
73, de Earl, K6SE