Cecil wrote:
This is just one more example of the dumbing down of amateur radio
accompanying the dumbing down of the US educational system in
general. Unfortunately, it seems to be a trend that cannot be
reversed because it is the biased view being pushed by the ARRL
and its supporters.

Hmmm...not sure I agree that the folks at ARRL are deliberately being
dumb (or maybe I just misunderstood you). Seems more unintentional to
me. After all, the technical editor of QEX let publish that bizarre
article that claimed to prove by math that phasing SSB receivers were
not possible. Can''t imagine a political motivation for that though I
have to wonder bigtime how that one got by. QEX really really needs
for some good peer review.

Ah, to have Ham Radio magazine back again. Loved that thing. Learned
most of my radio from it.

73,
Glenn AC7ZN

Funny thing is that I'm down with the slow-wave loading coil thing.
Maxwell's equations are your friend... not a very nice friend when
Bessel functions are involved, but...

Faster than light, though? Maybe the phase velocity in some tricky
cryogenic world, but I dunno...

Haven't seen much on superconducting antennas here... I read a paper
once with a superconducting magloop but they forgot to make the
matching network superconducting too.

Let's get the "bizarre but REAL" antenna thread going.

Wouldn't you like to have a QRP CW rig with a 3" magloop for 20m on the
top? The thermos full of liquid nitrogen is kind of a pain to lug
around...

Anyone built a "genetically" designed ham antenna yet? Might be a good
way to go for the "I have 50 feet between two trees to put up an 80m
dipole" crowd.

Maybe we could develop a combined performance+aesthetics genetic
algorithm to design efficient shortened vertical dipoles that look like
nice pieces of modern art and have a nice low voltage section to run
the coax out... you run the electromagnetic algorithm, weed out the
weak designs, then you have your neighbor click the most attractive
five and throw the rest out, and repeat!

-Dan

wrote in message
oups.com...
Cecil wrote:
This is just one more example of the dumbing down of amateur radio
accompanying the dumbing down of the US educational system in
general. Unfortunately, it seems to be a trend that cannot be
reversed because it is the biased view being pushed by the ARRL
and its supporters.

Hmmm...not sure I agree that the folks at ARRL are deliberately being
dumb (or maybe I just misunderstood you). Seems more unintentional to
me. After all, the technical editor of QEX let publish that bizarre
article that claimed to prove by math that phasing SSB receivers were
not possible. Can''t imagine a political motivation for that though I
have to wonder bigtime how that one got by. QEX really really needs
for some good peer review.


I don't think anyone is trying to be "deliberately being dumb", more like
"naturally being dumb" and not knowing it. :-)
Reality is that quality of technical material in ham publications is
slipping, heading for stuck on stupid. Add cheapening of ham ticket exams,
push for mass and no exam recruiting of new hams (a la CB wizards) in effort
to boost numbers and few bad apples with it - you get the picture of
deteriorating standards.

When W8JI had a presentation at Dayton's Antenna Forum and spoke about his
"famous - same current along the antenna loading coil", I came to K3LR
(forum leader) and N6BV (ARRL Antenna Book editor) and pointed out that
perhaps there is an error in W8JI assertions, I got this in private mail
from the "guru":

"When you pull people aside at Dayton to bitch about me or others or make
wild crazy statements it just makes you look worse and worse to the people
you are trying most to impress. At Dayton two years ago several people came
up and told me your tried to start conversations about me with them, or that
you started bitching about me."

Sooo, looks like one has to take some articles in ARRL publications with
biiiig grain of salt. Goofy stuff gets through, real expert material gets
swept under by "know-it-alls" in charge, Goofy is right and Right is not
important anymore. "Gurus" beat their drums into the publications and great
confusion ensues.

As far as SWR, I always tried to avoid it by matching, designing antennas to
have impedance of the feedline, and the TX/Amp output matching the feedline
impedance. Standing Wave Ratio always implied two waves - forward and
reflected and their superposition. Why waste power in "confused" standing
waves, when I can make sure that the waves are marching forward towards the
antenna and be radiated. Let the waves stand in the antenna, where they
belong, doing radiating and not in the lossy feedline.
High SWR is not imaginary, it is real, can create excessive voltages,
dielectric losses and melt the coax.

Happy Mother's Day to all the mothers that did not abort us!
God Bless them and thank you!

Yuri, da BUm

wrote:
Hmmm...not sure I agree that the folks at ARRL are deliberately being
dumb (or maybe I just misunderstood you).

Let me just relate my personal experience. I submitted an article
to QEX which mentioned light wave theory as explained in "Optics",
by Hecht. An (un-named) QEX employee, with whom I was dealing, had
"Optics" as a college textbook and was very interested in the subject.
He suggested that I expand the light wave theory section of my article,
which I did. After about four revisions, he suddenly stopped responding
to my emails. A couple of months later, I received a rejection letter.
That was well over a year ago.

Two QEX articles have recently appeared covering exactly the same
material as my article but with different slants. QEX still will
not answer my emails and will not publish my letters to the editor.
My treatment by QEX is more akin to religious shunning than
anything else.

I am convinced that the QEX employee that I was dealing with is
deliberately publishing dumbed-down material because he previously
indicated that he knows different from his college optics course.
He is most probably being directed to do so by his superiors because
he was, at first, enthusiastic about publishing my article which
is available from my web page below.
--
73, Cecil http://www.qsl.net/w5dxp/energy.htm

Yuri Blanarovich wrote:
When W8JI had a presentation at Dayton's Antenna Forum and spoke about his
"famous - same current along the antenna loading coil", ...

It is unusual for W8JI to give up on an argument so abruptly. I
wish I had thought of the dual-Z0 shortened stub concept years ago.
--
73, Cecil http://www.qsl.net/w5dxp

tell us more, 'dual-z0 shortened stub' sounds like something interesting.

"Cecil Moore" wrote in message
. com...
Yuri Blanarovich wrote:
When W8JI had a presentation at Dayton's Antenna Forum and spoke about
his "famous - same current along the antenna loading coil", ...

It is unusual for W8JI to give up on an argument so abruptly. I
wish I had thought of the dual-Z0 shortened stub concept years ago.
--
73, Cecil http://www.qsl.net/w5dxp

Dave wrote:
tell us more, 'dual-z0 shortened stub' sounds like something interesting.

In my quest to explain the phase shift in a 75m bugcatcher
coil, I thought about a dual-Z0 stub. The shortest 450/50 one
I have come up with that causes the maximum phase shift is:

---19 deg of 450 ohm line---+---18 deg of 50 ohm line---open

Believe it or not, that is an electrical 1/4WL stub with a
whopping 53 degrees of *lossless* phase shift occurring at the
'+' impedance discontinuity point. Are there any applications
for a stub that is physically 0.1 WL long instead of 0.25WL?

It could be shortened even more by using 600 ohm line with
50 ohm line. On top of everything else, the current in the
50 ohm section seems to be much lower than the current in
the 600 ohm section thus reducing the losses in the stub.

From these experiments, I have concluded that the phase shift
in a 75m mobile loading coil may be in the ballpark of 20 degrees
while the phase shift in the stinger is in the ballpark of 20
degrees with the majority of phase shift coming from the
impedance discontinuity between the loading coil and the stinger.
So neither side of the years-long argument was right or wrong.
--
73, Cecil http://www.qsl.net/w5dxp

En/na Dave ha escrit:
... Come on, just a little fight???

Just a question about coax cables:

I know that a coax cable does not radiate (if common mode currents
properly suppressed) because both conductors are apparently "in the same
place" (wouldn't know how to express it in more technical terms).

Now the question is: This is true for big distances from the coax, but
is it also true when you get very close to the coax? Imagine a conductor
taped to the outside of a coax for some meters. The capacitive coupling
to the braid is much higher than the coupling to the inner conductor.
Would it pick some of the current in the coax. If not, why not?

(apart from fun I'm really interested in the answer as I'm not quite
sure if a coax running parallel to unshielded and not twisted computer
cables would pick harmonics from it on RX or create interferences on TX)

--
Toni

no... and yes.... there would be some pickup, but only from leakage through
an imperfect braid. because the current is on the inside of the shield it
would not couple to the cable on the outside. the electric and magnetic
fields are contained completely inside the shield.


"EA3FYA - Toni" wrote in message
...
En/na Dave ha escrit:
... Come on, just a little fight???

Just a question about coax cables:

I know that a coax cable does not radiate (if common mode currents
properly suppressed) because both conductors are apparently "in the same
place" (wouldn't know how to express it in more technical terms).

Now the question is: This is true for big distances from the coax, but is
it also true when you get very close to the coax? Imagine a conductor
taped to the outside of a coax for some meters. The capacitive coupling to
the braid is much higher than the coupling to the inner conductor. Would
it pick some of the current in the coax. If not, why not?

(apart from fun I'm really interested in the answer as I'm not quite sure
if a coax running parallel to unshielded and not twisted computer cables
would pick harmonics from it on RX or create interferences on TX)

--
Toni

EA3FYA - Toni wrote:

Just a question about coax cables:

I know that a coax cable does not radiate (if common mode currents
properly suppressed) because both conductors are apparently "in the same
place" (wouldn't know how to express it in more technical terms).

Here's why it doesn't radiate: In a coaxial cable with a solid shield,
the differential mode current is entirely inside the shield. Current and
fields penetrate only a very small distance from the inner surface of
the shield, and no significant amount ever makes it through to the
outside. This is assuming that the shield is at least several skin
depths thick, which is a good assumption at HF and above.

Common mode current, by contrast, flows on the outside of the shield,
and its field radiates outward from there.

Now the question is: This is true for big distances from the coax, but
is it also true when you get very close to the coax? Imagine a conductor
taped to the outside of a coax for some meters. The capacitive coupling
to the braid is much higher than the coupling to the inner conductor.
Would it pick some of the current in the coax. If not, why not?

Again assuming a solid shield -- the center conductor carries a current
and therefore creates a field. The inner surface of the shield carries
an equal and opposite current and also creates a field. But those fields
are equal and opposite, and cancel at all points beyond a thin layer on
the inner surface of the shield. Since there's no significant field at
any point outside the shield, it doesn't matter where you look, you
won't find any, and there isn't any field to couple to anything else.

In reality, any shield other than a completely solid one (such as the
shield of hard line or semi-rigid coax) will leak some because of gaps
or holes. And the field will couple more strongly to wires which are
close than those which are far away. Whether the amount of leakage is
significant or not depends on the application.

(apart from fun I'm really interested in the answer as I'm not quite
sure if a coax running parallel to unshielded and not twisted computer
cables would pick harmonics from it on RX or create interferences on TX)

You might get enough leakage through the shield of ordinary coax to
cause problems in both cases. It depends on the transmit power level,
the signals in the wires, the length over which they're bundled, the
frequencies involved, the quality of the shield, and so forth.
Separating them even a small distance would reduce the coupling
considerably. But you're likely to have more trouble with common mode
current.

Roy Lewallen, W7EL