"John Smith" wrote in message
...

snip

However, a 1/2 monopole with a gamma feed is what I
finally settled on and still run today. Benefit is that this antenna
requires a minimal counterpoise for excellent performance and radiation
pattern and ease of construction.

Regards,
JS


I need to learn more aboout matching. I picked up the 1989 edition of
ARRL's ANTENNA IMPEDANCE MATCHING at the swap meet a few years ago, but I
really haven't taken the time to dig into it.

I'm starting to think in terms of Smith charts, which I never thought I
would need or use. Surprise!

Sal M. Onella wrote:
I'm starting to think in terms of Smith charts, which I never thought I
would need or use. Surprise!

Carrying a Smith Chart around in your head is a
good way to conceptualize transmission line and
antenna configurations.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
...
Sal M. Onella wrote:
I'm starting to think in terms of Smith charts, which I never thought I
would need or use. Surprise!

Carrying a Smith Chart around in your head is a
good way to conceptualize transmission line and
antenna configurations.
--
73, Cecil http://www.w5dxp.com

Yes. I have seen a lot of Smith charts for broadband Navy shipboard
antennas. The people who match them obviously have to do a chart for the
raw antenna in place on the ship, then design and adjust a matching network,
followed by a chart of the results, with every point inside the 3:1 (or 4:1)
circle. Their efforts are generally documented in the ships' antenna files.

I agree about the Smith chart for conceptualizing but at this stage, I am
just a Smith baby.

Back on topic, I am using the sleeve in a conventional dipole configuration
until I can take the time to apply the ideas presented in this NG. I
noticed this afternoon that coiling four turns of decoupling loop a few feet
from the feed actually raised the VSWR, which I didn't understand. Also,
where the coax hangs down next to the antenna makes a difference in the
VSWR, so obviously the line is not "flat" and is instead part of the
antenna. (Do we still use the term "flat" to describe a transmission line
which is properly matched to the load? I recall it from Navy training more
than 40 years ago.) My first HF antenna works, but it's clearly no marvel.

"Sal M. Onella" wrote in
:


"Cecil Moore" wrote in message
...
Sal M. Onella wrote:
I'm starting to think in terms of Smith charts, which I never
thought I would need or use. Surprise!

Carrying a Smith Chart around in your head is a
good way to conceptualize transmission line and
antenna configurations.
--
73, Cecil http://www.w5dxp.com

Yes. I have seen a lot of Smith charts for broadband Navy shipboard
antennas. The people who match them obviously have to do a chart for
the raw antenna in place on the ship, then design and adjust a
matching network, followed by a chart of the results, with every point
inside the 3:1 (or 4:1) circle. Their efforts are generally
documented in the ships' antenna files.

I agree about the Smith chart for conceptualizing but at this stage, I
am just a Smith baby.

Back on topic, I am using the sleeve in a conventional dipole
configuration until I can take the time to apply the ideas presented
in this NG. I noticed this afternoon that coiling four turns of
decoupling loop a few feet from the feed actually raised the VSWR,
which I didn't understand. Also, where the coax hangs down next to
the antenna makes a difference in the VSWR, so obviously the line is
not "flat" and is instead part of the antenna. (Do we still use the
term "flat" to describe a transmission line which is properly matched
to the load? I recall it from Navy training more than 40 years ago.)

Yes, I think that the meaning taken for a "flat line" is one with 1:1 or
close VSWR, flat to mean the magnitude of the voltage (or current) is
approximately constant all all positions on the line, and that describes
only what is happening on the inside of the line. That doesn't preclude
current flowing on the outside of the line which seems to be your issue.
I won't confuse you with examples of where the outside of the line is
intended to carry current and at the same time the VSWR is low, but it is
possible and sometimes desired.

I agree with you that if you change the feedline routing physically, and
you see a consequent change in VSWR, that suggests the outside of the
feedline carries current and is part of the radiating system, and I don't
think that is what you want.

My first HF antenna works, but it's clearly no marvel.

Look upon it as an opportunity for learning. After all, what would you do
if it just worked?

Owen

"Owen Duffy" wrote in message
...


Look upon it as an opportunity for learning. After all, what would you do
if it just worked?

Head off to another band, perhaps? Make more and start passing them out?
But you're right, of course. I still have three or four suggestions to try
for the sleeve.

"Sal M. Onella" wrote in
:

Back on topic, I am using the sleeve in a conventional dipole
configuration until I can take the time to apply the ideas presented
in this NG. I noticed this afternoon that coiling four turns of
decoupling loop a few feet from the feed actually raised the VSWR,
which I didn't understand. Also, where the coax hangs down next to
the antenna makes a difference in the VSWR, so obviously the line is
not "flat" and is instead part of the antenna. (Do we still use the
term "flat" to describe a transmission line which is properly matched
to the load? I recall it from Navy training more than 40 years ago.)
My first HF antenna works, but it's clearly no marvel.

I just read your first posting. It sounds like you are building what I
refer to as a coaxial dipole. The key to success with coaxial dipoles is
decoupling the feedline. A common configuration is to place a set of
radials, or a quarter wave choke to be effective a quarter wave below the
bottom of the dipole lower element... this actually attempts to reduce
current below the radials, and uses the quarter wave of feedline above
the radials as part of the radiator for a little more gain.

IIRC, the ARRL had some suggestions about decoupling a coaxial dipole.

Owen

Sal M. Onella wrote:
"Owen Duffy" wrote in message
...

Look upon it as an opportunity for learning. After all, what would you do
if it just worked?

Head off to another band, perhaps? Make more and start passing them out?
But you're right, of course. I still have three or four suggestions to try
for the sleeve.



Sal:

I thought it might be clear from my previous post, but I see it was
rather "cryptic."

I DID find that the coax wanted to couple into the antenna and become
part of it (the sleeve itself was NOT a sufficient de-coupling device.)
I found the 1:1 current balun was absolutely necessary to make the
antenna "stable"--remove the sensitivity to
location/orientation/length/etc. of the coax feed.

JS

"Owen Duffy" wrote in message
...
"Sal M. Onella" wrote in
:

Back on topic, I am using the sleeve in a conventional dipole
configuration until I can take the time to apply the ideas presented
in this NG. I noticed this afternoon that coiling four turns of
decoupling loop a few feet from the feed actually raised the VSWR,
which I didn't understand. Also, where the coax hangs down next to
the antenna makes a difference in the VSWR, so obviously the line is
not "flat" and is instead part of the antenna. (Do we still use the
term "flat" to describe a transmission line which is properly matched
to the load? I recall it from Navy training more than 40 years ago.)
My first HF antenna works, but it's clearly no marvel.

I just read your first posting. It sounds like you are building what I
refer to as a coaxial dipole. The key to success with coaxial dipoles is
decoupling the feedline. A common configuration is to place a set of
radials, or a quarter wave choke to be effective a quarter wave below the
bottom of the dipole lower element... this actually attempts to reduce
current below the radials, and uses the quarter wave of feedline above
the radials as part of the radiator for a little more gain.

IIRC, the ARRL had some suggestions about decoupling a coaxial dipole.

Owen

I was thinking it might be interesting to make a ferrite choke that you can
slide on the coax to tune the antenna. You might not have to slide the whole
choke just a bead or two that you can move a few inches.

Jimmie.

On Feb 26, 10:23 pm, Owen Duffy wrote:
That doesn't preclude
current flowing on the outside of the line which seems to be your issue.
I won't confuse you with examples of where the outside of the line is
intended to carry current and at the same time the VSWR is low, but it is
possible and sometimes desired.

Yep, SWR and feedline decoupling are pretty much totally unrelated.
It's possible to have a great match, and horrible decoupling from the
line.
And visa versa.. Or versa versa, or visa visa..

JS ruminated
I DID find that the coax wanted to couple into the antenna and become
part of it (the sleeve itself was NOT a sufficient de-coupling device.)

It's not a decoupling device at all really. It's the lower half of the
antenna. A sleeve
half wave needs additional sleeves for decoupling. There are quite a
few
commercial variations that can be looked at. Many were built as heavy
duty VHF public service type antennas. The extra decoupling sleeves
can
be applied to the usual ground planes also. For VHF, etc, I usually
prefer using
sleeves, cones, radials, etc vs the usual rf choke or beads.
MK

"Jimmie D" wrote in message
...

"Owen Duffy" wrote in message

snip

The key to success with coaxial dipoles is
decoupling the feedline. A common configuration is to place a set of
radials, or a quarter wave choke to be effective a quarter wave below
the
bottom of the dipole lower element... this actually attempts to reduce
current below the radials, and uses the quarter wave of feedline above
the radials as part of the radiator for a little more gain.

IIRC, the ARRL had some suggestions about decoupling a coaxial dipole.

Owen

I was thinking it might be interesting to make a ferrite choke that you
can
slide on the coax to tune the antenna. You might not have to slide the
whole
choke just a bead or two that you can move a few inches.

Jimmie.

This is worth trying, too and I had thought of it. Too bad I don't what type
ferrite material I have (all junk-box recoveries, swap meet, etc). I
figured on a low probability of success, but with failure so cheap, quick
and easy -- what the heck!. ;-)