Isopole question--1 cone vs. 2
Peter J. Bertini
service, but I wish to use only one of the two decoupling
cones. (Missing cone, tower loading and vertical space
issues...)..
How much does the second cone really add to the antenna's
performance (they did make an Isopole Jr. at one time with
one cone for some bands) and I will I notice the difference?
Unfortunately, since the antenna is discontinued I can't find
much info on the net regarding its design.
Anything I can do to further improve decoupling in lieu of the
second cone (ferrite sleeves on the coax, insulated mast?)
--
Peter, K1ZJH
Dan Richardson
used for decoupling.
Danny, K6MHE
Peter J. Bertini
first cone mounted around 25 inches down the mast?
I would have expected it should have been mounted
directly beneath the bottom of the 5/8th wave radiator
if it was the lower element...
Pete
"Dan Richardson" <k6...@arrl.net> wrote in message
news:kc90ot0nhvogfei3a...@4ax.com...
Peter J. Bertini
would be located, and isolate the coax line using a Collins or
ferrite bead choke in lieu of the lower decoupling cone?
Pete
"Dan Richardson" <k6...@arrl.net> wrote in message
news:kc90ot0nhvogfei3a...@4ax.com...
Crazy George
quarter wave sleeve, would decouple the antenna from everything below it
without having to do anything to the mast. I think the designers were
looking for two things,
1. Something different enough to be patentable, and
2. Small overall diameter.
21" radials will make it 42" in diameter, and unsightly.
There's not much ferrite which will do what you anticipate at that
frequency.
--
Crazy George
Remove NO & SPAM from automatic address when replying directly.
Peter J. Bertini <comm...@home.com> wrote in message
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Mark Keith
>
> I really don't understand how this thing works--why is the
> first cone mounted around 25 inches down the mast?
> I would have expected it should have been mounted
> directly beneath the bottom of the 5/8th wave radiator
> if it was the lower element...
>
> Pete
The bottom of the top cone is the lower end of the bottom 5/8 waves
section. It's 25 inches down in order to make the "48+-?? inches for the
lower radiator. The lower cone is for decoupling.
I wouldn't delete the lower cone unless you don't mind a fairly good
drop in performance. The pattern will skew up off the horizon due to the
currents from the feedline. I haven't tested the difference on the
isopole, but I have tried this on the dual 5/8 ringo ranger/RR2.
Deleting the decoupling section on the RR2 and converting it to a plain
old ringo ranger caused a large drop in performance here. MK
--
http://web.wt.net/~nm5k
Roy Lewallen
to the feedline below. I suspect this would also happen with a sleeve.
Using baluns, it requires at least two, one at the feedpoint and a
second about a quarter wave below, to reduce the coupled current to a
small value.
Roy Lewallen, W7EL
Tom W8JI
<muns...@attglobal.net.SPAM> wrote:
>I would think either a 4 set of 21" radials , or a choke, I. E., a backward
>quarter wave sleeve, would decouple the antenna from everything below it
>without having to do anything to the mast. I think the designers were
>looking for two things,
>
>1. Something different enough to be patentable, and
>
>2. Small overall diameter.
>
>21" radials will make it 42" in diameter, and unsightly.
>
>There's not much ferrite which will do what you anticipate at that
>frequency.
>
>--
>Crazy George
You'd be amazed at how much current is on the feedline below a four
radial groundplane antenna.
There are many VHF antennas that take advantage of that current to
produce gain. Isopole certainly wasn't the first by any means.
73 Tom
J. Harvey
> There are many VHF antennas that take advantage of that current to
> produce gain. Isopole certainly wasn't the first by any means.
I understood that such feedline currents tend to tilt the gain pattern up
into the sky wasting power where people weren't. The Isopole decoupled the
feedline and got the power down onto the horizon where the people were.
This made the effective (useful) gain better. This is all based on fuzzy
recollection...
Dan Richardson
Its been awhile since I've had one but as I remember the decoupling
section is used to decouple the supporting mast. The feed line
(running down the inside of the mast) is not decoupled by this lower
stub. So feed line common mode currents on the transmission line would
be unaffected. Least that's what I *think* happens ;-)
Danny
Peter J. Bertini
> On Mon, 20 Aug 2001 01:26:04 -0500, Mark Keith <> Its been awhile since
I've had one but as I remember the decoupling
> section is used to decouple the supporting mast. The feed line
> (running down the inside of the mast) is not decoupled by this lower
> stub. So feed line common mode currents on the transmission line would
> be unaffected. Least that's what I *think* happens ;-)
>
> Danny
>
>
being used in a vertical colinear fashion, with the first cone
being part of the lower radiator and also to provide some decoupling
from the mast as well. The feedline is inside of the mast, so
the common mode currents would be flowing on the mast.
Pete
Mark Keith
>
> Its been awhile since I've had one but as I remember the decoupling
> section is used to decouple the supporting mast. The feed line
> (running down the inside of the mast) is not decoupled by this lower
> stub. So feed line common mode currents on the transmission line would
> be unaffected. Least that's what I *think* happens ;-)
>
> Danny
It should be decoupling the mast and feedline both. Usually the coax
would be coming out of the mast well above ground I think. It would
still be prone to radiation on the shield. Also if the mast radiated,
but not the coax, there really wouldn't be much difference as far as the
overall effect. The pattern would still skew upwards in most cases.
Either one will hurt the performance. MK