"JIMMIE" wrote in message
oups.com...


snip

One thing that
concerned me even after the antenna was working is the SWR
appeared to be a little too good. It was 1.2:1 in the middle of 10
meters and never got ave 1.7:1 even at the band edges. I thought that
this is a little too good to be true..

My concern, too, for the same reason but the readings appear to be
authentic. For check, I tried the modified antenna (coax not running
through the lower element) on a few other bands with very, very low power
and got terrible VSWR readings. I get about a 1.4:1 at the low end of the 10
band, dropping to a 1.1:1 near the top of the band. I believe having big,
fat elements helps.

Due to cable loss, my measured VSWR at the transceiver is a skosh better
than what I would see at the antenna. A nice chart in the ARRL Antenna Book
shows that with 1 dB cable loss (approximate for 100' of RG-8), my 1.4:1
VSWR measured at the radio is actually closer to 1.6 at the antenna. Still a
keeper. I went on the air last night with a few watts and got a great
signal report from a local ham, so the antenna is working.

"Sal"
(KD6VKW /AE)

Sal M. Onella wrote:
"JIMMIE" wrote in message
oups.com...


snip

One thing that
concerned me even after the antenna was working is the SWR
appeared to be a little too good. It was 1.2:1 in the middle of 10
meters and never got ave 1.7:1 even at the band edges. I thought that
this is a little too good to be true..

My concern, too, for the same reason but the readings appear to be
authentic. For check, I tried the modified antenna (coax not running
through the lower element) on a few other bands with very, very low power
and got terrible VSWR readings. I get about a 1.4:1 at the low end of the 10
band, dropping to a 1.1:1 near the top of the band. I believe having big,
fat elements helps.

Due to cable loss, my measured VSWR at the transceiver is a skosh better
than what I would see at the antenna. A nice chart in the ARRL Antenna Book
shows that with 1 dB cable loss (approximate for 100' of RG-8), my 1.4:1
VSWR measured at the radio is actually closer to 1.6 at the antenna. Still a
keeper. I went on the air last night with a few watts and got a great
signal report from a local ham, so the antenna is working.

"Sal"
(KD6VKW /AE)




A year or two ago I was into playing with various monopole designs for
10 meters and greater freqs.

The bazooka I built and liked was a stainless steel whip for the
radiator. The bazooka sleeve was hook to coax and the mast--at the
sleeve where the bottom of the radiator was mounted on a teflon block
insulator. The sleeve was either 1-1/8 or 1-3/8 copper pipe.

The antenna was fed at the top of the sleeve where the radiator exited,
with a 1:1 current balun on a toroid core. The balun was able to handle
100+ watts and I drove it at 100 W.

The swr was below 1.5:1 on most of the ten meter band, I don't believe
it was ever above 2:1, if memory now serves me correct.

The antenna was ok. 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

"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.

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

"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

"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.