Jim exclaimed:
Bull----. It is NOT a bazooka, it is a simple ground plane with bent over
rods.

STOP TRYING TO CONFUSE THE GUY. It is a simple ground plane with
removable
radials. STOP POSTING ABOUT THE STUPID BAZOOKA.

Jim

Jim:

Alright, it's not a bazooka; it's a decoupling sleeve (thank you for the
enlightenment). Semantics aside, it will do what the OP wishes it to, and
in a physical representation that will work within his constraints.

Regards,
Bryan

"Bryan" wrote in message
...
Jim exclaimed:
Bull----. It is NOT a bazooka, it is a simple ground plane with bent
over
rods.

STOP TRYING TO CONFUSE THE GUY. It is a simple ground plane with
removable
radials. STOP POSTING ABOUT THE STUPID BAZOOKA.

Jim

Alright, it's not a bazooka; it's a decoupling sleeve (thank you for the
enlightenment). Semantics aside, it will do what the OP wishes it to, and
in a physical representation that will work within his constraints.

Regards,
Bryan


Either way, do we know the impedance? That is an "easy build" and I want to
try some single-band, no-tuner HF antennas. I cut one for 350 MHz
receive-only some years back (for the Blue Angels' radios at an air show)
and it worked fine.

One more thing: Assuming a nominal 50 ohm match can usually be made, is
there any drawback to tuning the thing by making the braid a little longer
than calculated, moving the end of the braid up and down to find the best
match and then securing the end? I mean, if you don't mind a somewhat
lumpy-looking sleeve. (I'm a bit lumpy-looking, myself.) The decoupling
capacitance would be reduced by both the decrease in length and the increase
in spacing, but the changed value would be, in effect, part of the tuning.

"Sal"

Sal M. Onella wrote:

Bryan wrote:
Jim exclaimed:
Bull----. It is NOT a bazooka, it is a simple ground plane with bent
over
rods.

STOP TRYING TO CONFUSE THE GUY. It is a simple ground plane with
removable
radials. STOP POSTING ABOUT THE STUPID BAZOOKA.

Jim

Alright, it's not a bazooka; it's a decoupling sleeve (thank you for the
enlightenment). Semantics aside, it will do what the OP wishes it to,
and
in a physical representation that will work within his constraints.

Regards,
Bryan


Either way, do we know the impedance? That is an "easy build" and I want
to
try some single-band, no-tuner HF antennas. I cut one for 350 MHz
receive-only some years back (for the Blue Angels' radios at an air show)
and it worked fine.

One more thing: Assuming a nominal 50 ohm match can usually be made, is
there any drawback to tuning the thing by making the braid a little longer
than calculated, moving the end of the braid up and down to find the best
match and then securing the end? I mean, if you don't mind a somewhat
lumpy-looking sleeve. (I'm a bit lumpy-looking, myself.) The decoupling
capacitance would be reduced by both the decrease in length and the
increase
in spacing, but the changed value would be, in effect, part of the tuning.

"Sal"

It's a dipole, so it should look like 50-75 ohms to the feedline. I'm not
sure I follow your line of thinking in regard to moving the shield up/down.
Bryan

snip

"Bryan" wrote in message

I'm not
sure I follow your line of thinking in regard to moving the shield
up/down.
Bryan


Perhaps I am over-analyzing it. Here's what I meant:

To make the antenna, a quarter wave section of shield is exposed, then
inverted and pulled down over the outside of the coax jacket. If it's
pulled down TIGHT, it has maximum length and minimum spacing to the part of
the shield under the jacket, hence the greatest decoupling takes place, if I
understand the principle of the antenna.

However, what I alluded to earlier was moving the end of the shield up and
down as a tuning method. I said this because another poster said you tune
the thing by changing the length of the coax section and/or the shield
section; I was looking for a non-cutting method to change the length of the
shield portion and merely pushing the end upward seemed to be viable. (I'm
sure the shield is sufficiently flexible to allow this.) If the end of the
shield is pushed upward, it shortens the shield and should shift resonance
up.

So, I imagine I can cut the shield section for slightly more than a quarter
wave, then tune it as I described. The upper section can be tuned with
dikes and/or a soldering iron, as necessary.

"Sal"

Sal M. Onella wrote:

snip

Bryan wrote:

I'm not sure I follow your line of thinking in regard to moving the
shield
up/down.
Bryan


Perhaps I am over-analyzing it. Here's what I meant:

To make the antenna, a quarter wave section of shield is exposed, then
inverted and pulled down over the outside of the coax jacket. If it's
pulled down TIGHT, it has maximum length and minimum spacing to the part
of
the shield under the jacket, hence the greatest decoupling takes place, if
I
understand the principle of the antenna.

However, what I alluded to earlier was moving the end of the shield up and
down as a tuning method. I said this because another poster said you tune
the thing by changing the length of the coax section and/or the shield
section; I was looking for a non-cutting method to change the length of
the
shield portion and merely pushing the end upward seemed to be viable.
(I'm
sure the shield is sufficiently flexible to allow this.) If the end of
the
shield is pushed upward, it shortens the shield and should shift resonance
up.

So, I imagine I can cut the shield section for slightly more than a
quarter
wave, then tune it as I described. The upper section can be tuned with
dikes and/or a soldering iron, as necessary.

"Sal"

I "groc" you, now. Sure, why not?!
Bryan

On Sun, 31 Dec 2006 22:31:41 -0800, "Sal M. Onella"
wrote:

Either way, do we know the impedance? That is an "easy build" and I want to
try some single-band, no-tuner HF antennas.

Hi OM,

The sleeve dipole makes for a pretty tall HF radiator and puts one end
quite close to ground where a ground plane design, if you matched the
heights of the feed points, would probably show less loss.

As for impedance, it would be close to a conventional dipole - 70 to
75 Ohms. However, the proximity of earth (for HF) would alter that.
Further, the jacket material that covers the outer braid is notorious
for being rather lossy in its own right. When you draw the braid back
over it, it creates a lossy transmission line with that material
between the drawn back braid, and the jacketed braid it is covering.
This does not normally concern most who build this style of antenna as
it is one of those "precious" details that is argued endlessly while
others put it to good use.

One more thing: Assuming a nominal 50 ohm match can usually be made, is
there any drawback to tuning the thing by making the braid a little longer
than calculated, moving the end of the braid up and down to find the best
match and then securing the end?

It'll work just fine.

The decoupling
capacitance would be reduced by both the decrease in length and the increase
in spacing, but the changed value would be, in effect, part of the tuning.

This is the first I've heard of "decoupling capacitance." The lower
arm of the vertical dipole is just that, the lower arm. It's
proximity to the feed line will certainly impact the state of tune,
but there is no claim to decoupling built into this design. You will
have to provide for the usual considerations in that regard (but most
neglect that too to no particular pain).

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 31 Dec 2006 22:31:41 -0800, "Sal M. Onella"
wrote:

Either way, do we know the impedance? That is an "easy build" and I want
to
try some single-band, no-tuner HF antennas.

Hi OM,

The sleeve dipole makes for a pretty tall HF radiator and puts one end
quite close to ground where a ground plane design, if you matched the
heights of the feed points, would probably show less loss.

As for impedance, it would be close to a conventional dipole - 70 to
75 Ohms. However, the proximity of earth (for HF) would alter that.
Further, the jacket material that covers the outer braid is notorious
for being rather lossy in its own right. When you draw the braid back
over it, it creates a lossy transmission line with that material
between the drawn back braid, and the jacketed braid it is covering.
This does not normally concern most who build this style of antenna as
it is one of those "precious" details that is argued endlessly while
others put it to good use.

One more thing: Assuming a nominal 50 ohm match can usually be made, is
there any drawback to tuning the thing by making the braid a little longer
than calculated, moving the end of the braid up and down to find the best
match and then securing the end?

It'll work just fine.

The decoupling
capacitance would be reduced by both the decrease in length and the
increase
in spacing, but the changed value would be, in effect, part of the tuning.

This is the first I've heard of "decoupling capacitance." The lower
arm of the vertical dipole is just that, the lower arm. It's
proximity to the feed line will certainly impact the state of tune,
but there is no claim to decoupling built into this design. You will
have to provide for the usual considerations in that regard (but most
neglect that too to no particular pain).

73's
Richard Clark, KB7QHC

I made one of these sleeve antennas for 10M with the folded back shield,
put a KW on it and it arced through the black vinyl.
Not exactly what I would call a "precious detail". Many years ago Shakespear
antennas were made this way and they changed there design because of the
same problem. Now they replace the folded back sheild with 4 or 5 wires
imbeded in the fiberglass shell putting a good bit of air dielectric between
the folded back part of the dipole and the sheild.

Jimmie D wrote:
I made one of these sleeve antennas for 10M with the folded back shield,
put a KW on it and it arced through the black vinyl.

It's a standing wave antenna. The voltage at the end
of the shield is approximately 20 times the voltage
at the feedpoint. For a KW, that's more than 5 kV,
too much for ordinary coax.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
et...
Jimmie D wrote:
I made one of these sleeve antennas for 10M with the folded back shield,
put a KW on it and it arced through the black vinyl.

It's a standing wave antenna. The voltage at the end
of the shield is approximately 20 times the voltage
at the feedpoint. For a KW, that's more than 5 kV,
too much for ordinary coax.
--
73, Cecil http://www.w5dxp.com

No kidding!!!!!

Cecil Moore wrote:
Jimmie D wrote:
I made one of these sleeve antennas for 10M with the folded back
shield, put a KW on it and it arced through the black vinyl.

It's a standing wave antenna. The voltage at the end
of the shield is approximately 20 times the voltage
at the feedpoint. For a KW, that's more than 5 kV,
too much for ordinary coax.

Yeah, but tape a couple of ne-2 bulbs there and you can get that kool
old cb look when they light up on key down!!! silly grin

Regards,
JS