"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

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

"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.

I have 160 watts available. ... about 90 volts at the feedpoint, so a
whopping 1800 at the end of the shield. (Might want to keep the mike gain
throttled back.)

OR ... use a larger braid over a spacer of some kind and solder it to the
coax braid at the feedpoint. The spacer could be a piece of plastic pipe
slipped over the coax at the outset. Actually, the braid doesn't really have
to be braid. It could be a piece of copper pipe. The tuning operation
would need to be slightly different; I'll need to keep a few inches of the
original coax near the feedpoint. I'll tune it by sliding the pipes and
bunching up the coax at the feedpoint. Or tune it by adjusting the length of
the center conductor element.

I wonder ... if the pipe were sufficiently large, it would tend to broadband
the antenna. I know of this effect at UHF. How about 10m???

I'm looking forward to this. g

Thanks! I'll try to remember that. In the past RACES exercise, I was
stationed in the City Health Department Conference Room, which is Downtown
and practically under the local repeater towers. This is also why I was not
TOO worried about obtaining a particularly high gain antenna, and was more
concerned with being unobtrusive. However, inside that building, the rubber
ducky antenna worked, but just barely, so I took the mobile antenna off my
Tahoe and screwed it onto my HT, using an SMA to Coax adapter. That
received much better, but was a little unwieldly, plus it puts a little more
strain on the little SMA connector than I like. This little "TV Antenna
Feed Line" J-Pole should be just the ticket for any situation like this in
the future.

"Cecil Moore" wrote in message
. net...
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

..

I wonder ... if the pipe were sufficiently large, it would tend to
broadband
the antenna. I know of this effect at UHF. How about 10m???

I'm looking forward to this. g



Yes it does, solves some of the problem you have with the all coax type of
sleeve antenna. stuff some pieces of styrofoam inside the pipe to center the
coax. Wind a choke in you coax and it is a pretty decent antenna. Consider
this, make the sleve out of 2 inch conduit, at the middle of the antenna put
a cap on the pipe with a hole drilled to accept a mount for a whip, RS and
truck stops sell these. Bottom end screws into a 2inch PVC pullbox, other
side of the pullbox screws on another piece of pipe used as a mast. There
should be enough room in the pullbox for the choke.

Jimmie D wrote:
.
I wonder ... if the pipe were sufficiently large, it would tend to
broadband
the antenna. I know of this effect at UHF. How about 10m???

I'm looking forward to this. g



Yes it does, solves some of the problem you have with the all coax type of
sleeve antenna. stuff some pieces of styrofoam inside the pipe to center the
coax. Wind a choke in you coax and it is a pretty decent antenna. Consider
this, make the sleve out of 2 inch conduit, at the middle of the antenna put
a cap on the pipe with a hole drilled to accept a mount for a whip, RS and
truck stops sell these. Bottom end screws into a 2inch PVC pullbox, other
side of the pullbox screws on another piece of pipe used as a mast. There
should be enough room in the pullbox for the choke.



Or, just lengthen it out to a full wave dipole, provide a matching
circuit of your choice, add a 1:1 current balun and end up with a MUCH
more desirable antenna ...

Oh yeah, you still can use the ne-2 bulbs at either end (or both) of
this dipole and end up with that kewl "cb look!" satisfied look

moving on
JS

"Jimmie D" wrote in message
news:Bdymh.17679$_X.15840@bigfe9...

.

I wonder ... if the pipe were sufficiently large, it would tend to
broadband
the antenna. I know of this effect at UHF. How about 10m???

I'm looking forward to this. g



Yes it does, solves some of the problem you have with the all coax type of
sleeve antenna. stuff some pieces of styrofoam inside the pipe to center
the
coax. Wind a choke in you coax and it is a pretty decent antenna.
Consider
this, make the sleve out of 2 inch conduit, at the middle of the antenna
put
a cap on the pipe with a hole drilled to accept a mount for a whip, RS and
truck stops sell these. Bottom end screws into a 2inch PVC pullbox, other
side of the pullbox screws on another piece of pipe used as a mast. There
should be enough room in the pullbox for the choke.



That's a clever idea. I am recalling four turns as the spec for the
feedline choke at 2m. However, at 28 MHz, there's a lot less inductive
reactance in those same four turns. How many turns are we looking at for
the choke?

"Sal M. Onella" wrote in message
news:BFGmh.53728

I am recalling four turns as the spec for the
feedline choke at 2m. However, at 28 MHz, there's a lot less inductive
reactance in those same four turns. How many turns are we looking at for
the choke?


snip

.... answering my own question: 4 feet of RG-58, coiled into 6 - 8 turns.
[ARRL Antenna Handbook]

"Sal"