Richard Clark wrote in
:

On Sun, 09 Sep 2007 22:51:54 -0400, RJG wrote:

I bought 2 Slinky's to put a Slinky antenna together, and would love
to get comments and suggestions, (construction detail tips, care and
feeding, etc.) from anyone who has tried this type of antenna before.

I live in a second floor apartment and have limited HF antenna
options. I would love to hear recommendations for any other HF antenna
designs that would work well in this type of setting.

Classic wire-wound, air-cooled resistors.

You could do better with the various 1 meter diameter loops sold
commercially. Some might suggest mobile screwdriver designs clamped
to your balcony railing, but that isn't really the same sort of metal
bulk equivalent to a, say, Chevy Suburban which would be the principal
radiator. On a comparable price basis, the loops will be a better
investment for 40M and up (I don't recall any that suggest they cover
80M and certainly 160M is beyond the realm).

I made a 160m loop out of LMR400, using the capacitance of the inner-to-
outer conductor to resonate it. Made it two turns and wound a gimmick
match out of flat 4-wire phone cable onto it to fire it up. Very narrow,
but reasonably effective. Better than a hamstick, I think. It's about 3
feet in diameter.

My normal 80-10 meter set-up is a hamstick horzontally off the balcony
rail. The rail backs onto a stucco wall with underlying mesh, so the
"ground" although tilted sideways is vastly larger than the average car.
I'm going to try a screwdriver there because I like the idea of being
able to change bands from the operating position instead of needing to go
outside in whatever weather is happening at the moment.



A simple test for small (for their wavelength) antennas is to measure
their bandwidth. We will take the Slinkies as an example (and
certainly cheap enough to test this statement, and to see how they
perform both). A small antenna that would be efficient will also
exhibit a high Q. The loops mentioned, as I recall, generally exhibit
5 to 10KHz bandwidth. For the most part, they exhibit some of the
better efficiencies (although not as high as a standard dipole).

Yes, my 160m loop is almost too narrow for SSB.


--
Dave Oldridge+
ICQ 1800667

On Wed, 12 Sep 2007 22:20:43 GMT, Dave Oldridge
wrote:

I made a 160m loop out of LMR400, using the capacitance of the inner-to-
outer conductor to resonate it. Made it two turns and wound a gimmick
match out of flat 4-wire phone cable onto it to fire it up. Very narrow,
but reasonably effective. Better than a hamstick, I think. It's about 3
feet in diameter.

....

Yes, my 160m loop is almost too narrow for SSB.

Hi Dave,

Radiation resistance for a 1 meter loop at 1800 KHz is 23 microOhms.
If I were to interpret your BW to be 2 KHz (an antenna Q of 900); then
the Ohmic resistance would be 0.0225 Ohms (0.002 Ohms/foot). This
resistance is on par with #13 wire which has considerably less surface
area than the LMR400.

The added resistance resides, undoubtedly, in connections (or maybe
the gimmick); and if you drove it out, you might find your loop
suitably more efficient for CW-only. Unfortunately, it might become
an arc-gap transmitter.

As an aside, I can't visualize the gimmick's relation to the
inner/outer conductors. You have any close-up pictures?

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

On Wed, 12 Sep 2007 22:20:43 GMT, Dave Oldridge
wrote:

I made a 160m loop out of LMR400, using the capacitance of the
inner-to- outer conductor to resonate it. Made it two turns and wound
a gimmick match out of flat 4-wire phone cable onto it to fire it up.
Very narrow, but reasonably effective. Better than a hamstick, I
think. It's about 3 feet in diameter.

...

Yes, my 160m loop is almost too narrow for SSB.

Hi Dave,

Radiation resistance for a 1 meter loop at 1800 KHz is 23 microOhms.

Two turns makes it 92 micro-ohms.

If I were to interpret your BW to be 2 KHz (an antenna Q of 900); then
the Ohmic resistance would be 0.0225 Ohms (0.002 Ohms/foot). This
resistance is on par with #13 wire which has considerably less surface
area than the LMR400.

I'm not sure it is as wide as 2khz. LIS, it's not really suitable for
SSB. It's OK on CW, though.

The added resistance resides, undoubtedly, in connections (or maybe
the gimmick); and if you drove it out, you might find your loop
suitably more efficient for CW-only. Unfortunately, it might become
an arc-gap transmitter.

I'd not recommend it for low power.

As an aside, I can't visualize the gimmick's relation to the
inner/outer conductors. You have any close-up pictures?

Look at Ted Hart's loop design in the old Antenna books. I sort of
patterned it after that. The 80 meter 1-turn loop is a bit bigger and,
of course works a bit better. Don't get me wrong, these were test-of-
concept antennas and I don't use them for my working antennas. If I were
to build a working loop for 80m, I'd do it out of 2-inch copper pipe and
make it as large as practical.


--
Dave Oldridge+
ICQ 1800667