Welding Rod J-Pole Possible? (alternate antenna)
 

hi

don't want to talk you out of the jpole but have you seen the

Moxon for 2m ? Direct fed with 50 ohm coax.

http://www.cebik.com/moxon/moxbld.html

has gain similar to a 2 element yagi but takes up less space,
and no radials to worry about.


73 jake

Welding Rod J-Pole Possible?
 

Yep, this is exactly what I'm looking for. Thanks!

"Bryan" wrote in message
...
Chuck James wrote:
This looks like what i am asking for, but the picture is not very clear.
Any more details anywhere?

Hi Chuck,

I found the image he
http://www.alpharubicon.com/elect/vertdipoleniet.htm
and cleaned it up -- not much more info available on that page. It's
basically a dipole turned vertical. With the feedline going thru the
bottom
half and connecting at the top of that section, it becomes a "bazooka"
vertical.

There're more links to bazooka antennas he
http://www.dxzone.com/catalog/Antennas/Bazooka/ I thought this
construction
method: http://www.start.ca/users/ldblake/bazooka.htm was particularly
innovative. I don't think you'd need to use RG-8 as described -- just
about
any 50-ohm feedline would work fine.

73,
Bryan WA7PRC

Welding Rod J-Pole Possible?
 

"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"

Welding Rod J-Pole Possible?
 

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

Welding Rod J-Pole Possible?
 

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

Welding Rod J-Pole Possible?
 

One of the other posters in this thread gave me the solution to my quest,
and it was cheap, easy, small, and less than 1.3 SWR. It was a simple
dipole, made of a wooden block and welding rod. I took a piece of 3/4 inch
wood dowel, cut it to about 4 inches in length, drilled one hole in each end
(lengthwise). I left about 1/2 inch of wood between the holes I drilled, so
the welding rods would not touch. I inserted a 19 inch piece of welding rod
in each end. The overall length is about 38 and 1/2 inches. Then, in the
center of the dowel, I drilled two intersecting holes so that I could put
screws into the wood which would press against each piece of welding rod.
This kept the welding rods in place, and it also gave me a place to attach
the center wire and braid from an RG-58U Coax cable. I soldered two small
alligator clips, on the coax, so that I could just clip the coax to the
antenna. To take it apart, or put it together, all I need is a phillips
screwdriver.

I'd like to thank everyone for their help, in pointing me in the right
direction!

"RST Engineering" wrote in message
...
I'm sure you know what you want, and I'm sure you have all the lab
equipment necessary to calculate VSWR on an antenna inside a conductive
structure. I'm also sure you have built antennas for emergency and
portable use for fifty years, so you are on your own so far as I'm
concerned.

Cheap, easy, small. Pick two.

Best of luck; write if you get work.

Jim



"Chuck James" wrote in message
. net...
Thanks. I appreciate the suggestion, but I have built the antenna you
described, using welding rod, plus a 440 MHz (smaller version), but in a
crowded room the radials stick out farther than I want. I tried building
a TV antenna line J-Pole today, but the SWR was higher than I expected.
I haven't tried shortening it yet, but will when I get time. But I would
still have to find some way to hang it from the ceiling or something. I
really want something small, unobtrusive and cheap and easy to
build.standing and as small as practical. The Welding Rod antennas
made with 45
degree radials are a little bulky to move through congested hallways.
The idea is to make it portable enough to move from room to room as
needed. Long radials would impede moving through hallways.
Thanks in advance, KE5GEO

Welding Rod J-Pole Possible?
 

"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.

Welding Rod J-Pole Possible?
 

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

Welding Rod J-Pole Possible?
 

Well, I finally took the time to work on the "TV Antenna Feed Line" J-Pole
someone suggested. I got it down to less than 1.6 SWR, on 2 meter, and less
than 1.2 on 70 cm, by trimming it down 1/8 inch at a time. So now I have a
VERY portable dual band antenna, I can just roll up and stick in a small
"go bag". I tried it on my Yaesu VX-6R and was able to hit several local
repeaters, some, of them even on low power.

Thanks again to all that helped.

"Jimmie D" wrote in message
.. .

"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.

Welding Rod J-Pole Possible?
 

Chuck James wrote:
Well, I finally took the time to work on the "TV Antenna Feed Line" J-Pole
someone suggested. I got it down to less than 1.6 SWR, on 2 meter, and less
than 1.2 on 70 cm, by trimming it down 1/8 inch at a time. So now I have a
VERY portable dual band antenna, I can just roll up and stick in a small
"go bag". I tried it on my Yaesu VX-6R and was able to hit several local
repeaters, some, of them even on low power.

A little trick I learned in AZ - It will work better
on 440 if you slant it toward the repeater.
--
73, Cecil http://www.w5dxp.com