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March 11th 04, 07:36 PM

On Thu, 11 Mar 2004 19:16:27 GMT, (Space
Charge) wrote:

I live on a small plot in a canyon (very steep canyon walls), and
between the tiny plot, CC&R's, and the very strong likelyhood of a
local chapter of Busybodies, Snoops and Ham-Haters (Local 557) being
present, the logical choice of antenna for 80M seemed to be either a
Magloop or a 6-slinky antenna w/a tuner, located inside the garage
running across the roof peak (only 20 feet).

Tried the slinky w/tuner, it loaded up just fine, but it turned out to
be a very good dummy load on 80M, and little else. Noisy as all
getout, too, mostly just gets local QRN.

Question: Will the 80M Magloop be any better, or should I just save my
effort and try something else?

Thanks to the group,

Lin/KJ6EF

Hi Lin,

Small antennas of any design (that is dipole or loop) suffer from the
amount of power that goes to radiation compared to the power that goes
up in heat. Without more geometrical details (like what is the
maximum length dipole, or the greatest perimeter of loop you can
support) speculations could run from dismal to aggressively tepid.

Let us consider you building a small 1Meter diameter loop from 1 inch
stock copper tubing:
Fo 1M diameter Efficiency with skin effect loss
160M 29 µOhms 0.2%
80M 500 µOhms 2.4%
60M 1.5 mOhms 6%
40M 7.5 mOhms 21%
30M 24 mOhms 42%
20M 120 mOhms 75%

The second column with the µOhms leading the way show the radiation
resistance for that band. At low frequencies it is so small that even
the low resistance of this large conductor wipes it out! The same
applies for a short dipole (irrespective of it being a slinky, which
being steel wire of smaller diameter, makes it far worse).

In your place, I would suspend a stove pipe size dipole from the roof
beam and drive it with a small coupling loop. It will still be quite
High Q'd requiring frequent tuning to move about the band. Take care
to insulate/isolate the ends from combustible material.

73's
Richard Clark, KB7QHC