Hey, Rick
I read the articles you pointed me to. Here are some random thoughts
about them, and the talk. And antennas in general. Oh, and one or two
other things.
It seems to me that the difference between a "slot" and a "loop" lies in
how you feed it. NBC basically says that if you connect one side of the
feedline to one side of the loop and one to the other side of the loop,
it's shunt fed and, therefore, a "skeleton slot". Otherwise, they're
the same wires in the same arrangement and I would expect them to
perform similarly. He even says as much during the talk, although he
criticizes one delta loop he shows because it is fed at the bottom, and
if there's a current antinode halfway around the loop from the
feedpoint, then the feedpoint being close to the ground wouldn't make
any difference from the radiation angle. For me, the real value of the
talk was finally understanding how a slot worked and, well, what "shunt
fed" means. (I'm a viscous aerodynamicist by training, and I find all
these weird terms confusing.) Well, that and pointing out that I should
have bought the NanoVNA with the big screen instead of the small one. I
didn't even realize there were two.
Of course, on HF, the polarization of the signal is not very important
in most cases, and I don't think that the directionality of the antenna
is worth talking about. If you want a directional antenna, I like
KL7AJ's idea of putting up two vertical antennas and driving them with a
specified phase shift to send the signal where you want. (I think I saw
the idea in the "Receiving Antennas" book.)
Since I prefer to work low-bands, horizontal dipoles are not generally a
good choice for me. I found out about a thing called a "Terminated
Coaxial Cage Monopole" which the inventor (Martin Ehrenfried G8JNJ) says
will give a basically flat impedance curve and decent efficiency from
1.8 to 70 MHz, and I've been considering building one of those, although
it is both bigger than the loop (or the slot) antenna and requires radials.
https://www.tc2m.info/
I'm not going to build it any time soon, however because I have built,
but haven't yet installed, a vertical monopole antenna which will be
made broadband by the simple expedient of feeding it through a remote
antenna tuner at the base. It's made of a lot of wire turned around
two-inch PVC pipe, so I expect that it will tune up on 160, but I have
no idea how efficient it might be. For a long time, I've toyed with the
idea of vertical dipole antennas in order to avoid laying out radials,
but eventually I concluded that creating a vertical support was the hard
part of building a vertical antenna and a vertical dipole is twice as
tall meaning that the construction of the antenna is at least twice as
hard. Radials are easier simply because they lie upon the ground. One
advantage of the slot (or the loop) is that you can make the antenna
wide in addition to tall, which means you don't have to go as tall.
On 3/13/21 8:16 PM, Rick Hiller via BVARC wrote:
Jonathan,
Have a read of this column
*http://www.bvarc.org/Tech/October2020.pdf
<http://www.bvarc.org/Tech/October2020.pdf>*
NBC is kind of pushing the slot take on this antenna. I disagree.
What'cha think?
Also see December 2020 The Radio Hotel in the Beacon
The paragraph on "Horizontally polarized vertically oriented
multi-band antenna"
.
Regards...Rick W5RH
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On Sat, Mar 13, 2021 at 3:48 PM Jonathan Guthrie via BVARC
<[email protected] <mailto:[email protected]>> wrote:
2 out of 4 now and the presentation on the skeleton slot antenna
was worth the cost of admission for me.
--
Jonathan Guthrie
ARS KA8KPN
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