On Fri, 18 Jan 2008 07:59:37 GMT, "Lee"
wrote:

I find my homebrew magloops r/x very well but don`t t/x too good!!! hence
the need for a larger directional ant on the rotator without encroaching on
neighbours space ....(too much) .... ;o)

Hi Lee,

I presume you mean by maploops, those that are only a meter or so in
diameter. You need a larger loop for 80M. A simple one turn with
plenty of surface area and low Ohmic contacts is preferred as anything
more complex invites massive loss.

The law with small antennas is their Radiation Resistance in relation
to their Ohmic Resistance. Most would grab some #12 wire and shrug it
off without a thought. That lack of thought generates calories in
heat. Some would add wire turns, the proximity of them merely
multiplies the heat, not the signal.

Either way the tune up seems great, but the results are miserable (no
doubt the source of your statement above). A good low band loop will
have a sharp tuning (narrow bandwidth). A poor low band loop will
appear to exhibit a great SWR for a broad bandwidth, You can test
this yourself with almost no effort at all.

Let's take that one meter diameter loop that is available from several
commercial outlets, and instead build it your self with house wire
(#12). The Radiation Resistance in the 80M band will be 528
millionths of an Ohm, Copper loss will be 16 thousandths of an Ohm
(not counting skin effect) - we still haven't computed connection
issues. Already, your copper loss is thirty times the radiation
resistance - I will let you delve into the issues of efficiency.

Doubling that loop diameter will double the copper loss to 32
thousandths of an Ohm, but what happens to Radiation Resistance? It
now runs more to 8 thousandths of an Ohm. The ratio has dropped from
30:1 to 4:1 in this doubling of size - even when the resistance of the
wire grew, the Radiation Resistance grew faster. Efficiency increases
dramatically.

Increase the loop size and use a larger conductor.

73's
Richard Clark, KB7QHC