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


For email responses, remove "nospam_".

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

Richard Clark wrote:
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.


Of course I don't know too many people that would want to operate 80
meters with a 1 meter magloop!

Lin, could you put up a larger magloop with maybe a 3 meter diameter?
Still not super, but a lot better. If you do it right, you might be able
to convince the locals that it is an art project!

- Mike KB3EIA -

On Thu, 11 Mar 2004 16:20:57 -0500, Mike Coslo wrote:


Of course I don't know too many people that would want to operate 80
meters with a 1 meter magloop!

Lin, could you put up a larger magloop with maybe a 3 meter diameter?
Still not super, but a lot better. If you do it right, you might be able
to convince the locals that it is an art project!

- Mike KB3EIA -

Hi Mike,

There is certainly no good reason to do it with a 1 meter loop, I will
agree. Others in this group may argue it is more efficient per unit
length (a blighted argument, Lin, take no notice of such claims).
However, the 1 meter size does conform to the commercial units offered
(although not for these low bands for good reason). Barring those
dimensions I suggested be revealed, we can continue.

Your simple tripling does a considerable difference by raising the
radiation resistance to all of 38 mOhms (which if we retain that same
1 inch copper tubing allows for much better efficiency and
consequently success. Care should be taken to observe this value is
roughly 2000 times smaller than the conventional dipole, and as such,
every effort should be applied towards keeping Ohmic losses low.

73's
Richard Clark, KB7QHC

You will find a magloop of the same order of size as a centre-loaded dipole
to have a much superior performance.

The disadvantage of the magloop is the high cost of the vacuum tuning
capacitor.

Program MIDLOAD will assist with design of a short centre-loaded horizontal
dipole. But it will only be a single-band job.

Program MAGLOOP4 will assist with design of a 1.5 or 2-metre square or
circular magloop for 80 meters which will also work even better on 40
meters. Use 1" diameter copper pipe.

Download programs in a few seconds from website below and run immediately.
The performances of the two types of antenna can be compared.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Reg Edwards wrote:

You will find a magloop of the same order of size as a centre-loaded dipole
to have a much superior performance.

The disadvantage of the magloop is the high cost of the vacuum tuning
capacitor.

Reg, since when does the tuning cap have to be a vacuum variable. There
are alternatives such as wide spaced variables, trombones, and other
ingeneous types.

Irv VE6BP
--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/
Visit my very special website at http://members.shaw.ca/finkirv4/
Visit my CFSRS/CFIOG ONLINE OLDTIMERS website at http://members.shaw.ca/finkirv5/
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Reg, since when does the tuning cap have to be a vacuum variable. There
are alternatives such as wide spaced variables, trombones, and other
ingeneous types.

Irv VE6BP

=========================

Not for a 1.5-metre diameter loop on 80m.

530 pF at 5000 volts.

Needs more than ingenuity.

I think you should move Lin. Way far off from there.

Butch

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


For email responses, remove "nospam_".