On Dec 3, 5:49 pm, "Tom Donaly" wrote:
Cecil Moore wrote:
K7ITM wrote:
Cecil, I posed two very specific examples for you to work out to show
us that you can actually correctly find the phase shift for travelling
waves, as you promised you could and would.

Sorry, Tom, when I came to the word "superconductor", I
stopped reading your posting. Please try to stick to
the real world of amateur radio next time. Anyone at
anytime can come up with some impossible esoteric
example that defies solution. Such examples are a
"vexations of the spirit" and I don't waste the
little time I have left on such nonsense. Please go
find another victim for your tarbaby.

In other words, you can't do it. Why don't you just say so?
73,
Tom Donaly, KA6RUH

It's his tarbaby, not mine. My description was just for an
inductively loaded antenna, and a capacitively loaded antenna. I was
simply describing a method by which I could make a very small high-Q
coil; the small capacitor can be had from DigiKey. The obvious
question is, does the size of the reactive loading component matter?
Then, if so, why, and to what degree?

What is it that loads (tunes) the antenna? Is it primarily the
inductance of the coil, or is it parasitic effects such as the coil's
capacitance to the outside world? Would the antenna be properly
loaded with pure inductance, or does it _require_ the parasitic
capacitance of the coil to the outside world?

By the way, there's another way I can place an inductive reactance at
a point in the antenna, in a way that it's not coupled to the outside
world: I can make the antenna conductor be the outside of a piece of
coaxial cable, and use the coaxial inside as a shorted stub which
reflects a pretty good (fairly high Q) inductive reactance back to a
particular point such as a quarter of the antenna length back from
each end, where the stub connects across a gap in the outer
conductor. Can I use such an inductive reactance to tune the
antenna? Will there then be a difference in current at each end of
the gap across which that reactance connects? If there is not, and
we're dealing with a standing-wave antenna, how do we account for all
the "electrical degrees" we need to--or do we really even need to be
counting "electrical degrees"?

(Joseph Boyer's wonderful article, "The Antenna-Transmission Line
Analog," is highly recommended here...)

Others are welcome to ponder all that while Cecil tries to unstick
himself from his tarbaby.

Cheers,
Tom

K7ITM wrote:
Others are welcome to ponder all that while Cecil tries to unstick
himself from his tarbaby.

It's your tarbaby, Tom, not mine. When you can tell me
what's the difference between a duck, I will tackle your
equally ridiculous questions.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
K7ITM wrote:
Others are welcome to ponder all that while Cecil tries to unstick
himself from his tarbaby.

It's your tarbaby, Tom, not mine. When you can tell me
what's the difference between a duck, I will tackle your
equally ridiculous questions.

Perhaps, said in olde' english it would gain more of your
interest/attention--"Shakespearian terms?" rofol

Cecil, don't take the whole world seriously, where would be the fun?

JS

John Smith wrote:
Cecil, don't take the whole world seriously, where would be the fun?

I'm sorry, John, the difference between a duck
is serious business. :-)
--
73, Cecil http://www.w5dxp.com

On Dec 3, 8:34 pm, Cecil Moore wrote:
....
It's your tarbaby, Tom, not mine.

Hey I'M not the one who's made well over a hundred postings in this
thread, man. Can the delusional see that they are? Have a good life;
I'll try in the future to not engage you in meaningful discussions
about your, um, tarbabies.

On Mon, 3 Dec 2007 18:29:24 -0800 (PST), K7ITM wrote:

I can make the antenna conductor be the outside of a piece of
coaxial cable, and use the coaxial inside as a shorted stub which
reflects a pretty good (fairly high Q) inductive reactance back to a
particular point such as a quarter of the antenna length back from
each end, where the stub connects across a gap in the outer
conductor. Can I use such an inductive reactance to tune the
antenna? Will there then be a difference in current at each end of
the gap across which that reactance connects?

Hi Tom,

Interesting proposition. I like it.

73's
Richard Clark, KB7QHC

On Dec 4, 10:23 am, Richard Clark wrote:
On Mon, 3 Dec 2007 18:29:24 -0800 (PST), K7ITM wrote:
I can make the antenna conductor be the outside of a piece of
coaxial cable, and use the coaxial inside as a shorted stub which
reflects a pretty good (fairly high Q) inductive reactance back to a
particular point such as a quarter of the antenna length back from
each end, where the stub connects across a gap in the outer
conductor. Can I use such an inductive reactance to tune the
antenna? Will there then be a difference in current at each end of
the gap across which that reactance connects?

Hi Tom,

Interesting proposition. I like it.

73's
Richard Clark, KB7QHC

Hi Richard,

Note that it's also possible to make the stub in the form of a helical
resonator operated below resonance--that is, a loading coil that's
shielded by the tubular conductor whose outside surface is the
antenna. A problem with using plain coax is that the length is
prohibitive. For example, if you make an 80-foot long dipole from
RG-213-size coax, you find that you need about 550 ohms reactance at
points a quarter of the total length in from the ends, to get it to
resonate at 3.9MHz. But using a shorted stub of 50 ohm line requires
about 85 electrical degrees of line. Even with solid polyethylene
dielectric, that's 39 feet of line. Ooops. We only have 20 feet to
work with. Lengthen the antenna to, say, 120 feet, and the required
reactance drops to a low enough value to be practical to do with a
shorted stub co-axial with the antenna wire, but at that point, why
bother? You'd only have to add a few feet of wire to get the antenna
to resonate without inductive loading.

Mostly I find value in thinking about things like this because they
make more clear what's really important: it's primarily the inductive
reactance that tunes the antenna; the parasitic capacitance from a
loading coil to the outside world, which is what causes it to behave
like a helical delay line, is of much lower importance in determining
the antenna tuning. In a long antenna that's capacitively loaded, the
capacitors can have negligible parasitic series inductance and shunt
capacitance to the outside world, but they still strongly affect the
antenna loading.

Of course, the closer to the end of the antenna you put a large
loading coil, the more effect its capacitance will have. In the
limit, you can dispense with the coil and just add a capacitive hat
after all. Even modest size conductive balls on the ends of a thin-
wire dipole will have a significant effect on the resonance.

Cheers,
Tom