How is it possible to decide whether or not a choke or balun is
needed, and where to locate it, unless the magnitude of what one MIGHT
wish to prevent is known.

I don't know about wattage, but measuring the
damage that a lack of decoupling does to the antenna
is easy to measure. Quite simple. Try each way,
and note the difference on a stable signal. The ringo
ranger without the lower section lost 3-4 S units
worth of performance in my case, using my line length.
Ditto for any other antenna. I found the decoupling of
simple 1/4 GP's can be improved also. Many, "including me"
often state that once a GP is at say 1/2 wave high, that only
3-4 radials are needed. As far as ground losses, this is true.
But the decoupling from the line can be further improved by
adding even more radials. Going from 4 radials to 8 usually
makes a noticable difference on a receiver...I consider a
receiver as just an poorly calibrated voltage meter in this
case. It's plenty good enough for A/B comparisons.
At HF, I don't worry about feedline radiation too awful much.
If I'm not torching my lips, wanking out my keyer, or causing light
bulbs to flicker in time to my CW or voice, I'm a happy camper.
Not so on VHF/UHF....I consider it critical if you want the best
performance. And....All this was tested in the real world by yours
truly...Over 20 years ago...I've had plenty of time to change my
stance...But I haven't...MK

wrote:
I found the decoupling of
simple 1/4 GP's can be improved also.

Quite often, one sees multiple turns of coax looped
under commercial elevated ground planes.
--
73, Cecil http://www.qsl.net/w5dxp

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Hi MK,

You seem a bit wound up... too much caffeine? ;-)

wrote in message
oups.com...
(snip)

Still others can't seem to understand that effects
too small to measure usually do not matter in the real world.

Total BS in most cases....I seen the lack of decoupling totally
ruin otherwise decent antennas... I've personally tested and
seen easy 3-4 s unit differences in the same exact antenna , with
and without the decoupling section connected.
Decoupling is critical to high performance on VHF/UHF.
All the best designs include it.

Let's see now. You say my proposition that an effect too small
to measure doesn't matter is "Total BS in most cases." Then
you give an "example" where the effect can not only be measured,
but the measured difference is very large "3-4 s unit(s)."

This strongly suggests that you did not understand the original
premise of "effects too small to measure." So let's try another
example, one far removed from antennas.

Let's say that ONE dust mite of 1,489,362 on your body at a
certain time decides to jump off while you're standing on the
bathroom scale--and that this event does not register on the scale.

I would say this too-small-to-measure event does not matter in
the real world. And even if you found a super laboratory scale
that actually could measure the mite departing, I would STILL
say the event does not matter. Your mileage may vary, of course.

Over in a digital camera forum I frequent, they have coined a
term to describe camera geeks who obsess about tiny differences
in camera system performance that have no practical significance
in real-world picture taking. The term is "measurebator."

Perhaps the term would also be useful in this NG. But we'll
probably have to add a new one of our own for the guys who
think modeling trumps practice. I suggest "modelbator."

Last but not least, if someone posts valid data showing that the
performance of an OSJ J-pole can be measurably, repeatably,
and significantly improved by a decoupling device, I'll be grateful
to him/her! And if the decoupling device is practical and affordable,
I'll want to know where to buy one, or how to build one.

Live long and prosper...

(snip)

You are
starting to attract imitators.

The J pole has been imitated numerous times....
Or are you talking about arrows?

My reference was to a guy in our area who is making exact
mechanical copies of the Arrow design. I suspect there are
others doing the same.

(snip)
MK

And even if you found a super laboratory scale
that actually could measure the mite departing, I would STILL
say the event does not matter. Your mileage may vary, of course.

Yes it varies a good deal...I'm not willing to throw away 3-4 S units
worth of low angle gain in the case of the ringo ranger.
It would take many mites to make up the difference.
Of course, the degree would vary to each persons
feedline. I was using about 50 ft.

Last but not least, if someone posts valid data showing that the
performance of an OSJ J-pole can be measurably, repeatably,
and significantly improved by a decoupling device, I'll be grateful
to him/her!

I've tested it, but I didn't collect data, other than in my head.
But there is no doubt that adding decoupling would make
the performance the same for any user. This will not be the
case without it. All decoupling will do is make sure you
get the gain you are supposed to. It's not going to help an
antenna that has little common mode problem to begin
with.

I suppose Al would have to have a poll....If the owners were
interested in the test...I don't really like J poles that much,
so I know I'm not going to waste my time repeating something
I did 20 years ago...

And if the decoupling device is practical and affordable,
I'll want to know where to buy one, or how to build one.

I've already described one simple version...I've tested it,
and I know it works. There are many ways you can do it..
MK

On Mon, 13 Jun 2005 22:54:01 GMT, "Old Ed"
wrote:

Don't let the nay-sayers in this NG bother you, and don't waste
your time arguing with them.

Some of them can't stand the thought that any antenna which differs
from their personal pet(s) might be good. Others can't grasp the
idea that when model predictions and actual results differ, it's the
results that count.

Spoken like a true naif.

I suggest that you would take the time to learn what causes common
mode current to be present on coax transmission line - regardless of
what kind of an antenna it is employed. (For openers I suggest you
start here http://www.w2du.com/r2ch21.pdf )

Then, after getting a grasp on that aspect continue to learn how
common mode current on the transmission line can effect the overall
performance of an antenna's radiation pattern - especially with VHF &
UHF antenna systems then you just might understand what people here
are trying to tell you.

However, I doubt that you would do that as it would appear you've made
up your mind and don't want to be confused with known facts.

Still others can't seem to understand that effects too small
to measure usually do not matter in the real world.

Others have measured this and reported it to you, but for some reason
you chosen to discount anyone who can show that it disagrees with your
"pet" theory. For me, I've place your theory along with the world is
flat, the moon is made of green cheese, and Iraq has weapons of mass
destruction .

But even for a skeptic, I would thing that the thought of coiling up a
few turns of coax costs very little, definitely won't hurt, and can
only help. Would be sufficient.

Danny, K6MHE

I suggest that you would take the time to learn what causes common
mode current to be present on coax transmission line - regardless of
what kind of an antenna it is employed. (For openers I suggest you
start here http://www.w2du.com/r2ch21.pdf )

Then, after getting a grasp on that aspect continue to learn how
common mode current on the transmission line can effect the overall
performance of an antenna's radiation pattern - especially with VHF &
UHF antenna systems then you just might understand what people here
are trying to tell you.

Still others can't seem to understand that effects too small
to measure usually do not matter in the real world.

Others have measured this and reported it to you, but for some reason
you chosen to discount anyone who can show that it disagrees with your
"pet" theory. For me, I've place your theory along with the world is
flat, the moon is made of green cheese, and Iraq has weapons of mass
destruction .

But even for a skeptic, I would thing that the thought of coiling up a
few turns of coax costs very little, definitely won't hurt, and can
only help. Would be sufficient.

Danny, K6MHE

I said I was done with this subject, But ........ I can't take it
anymore.
Again, the Arrow Antenna OSJ Antenna does NOT need a choke balun.
By that I mean it will make no noticeable difference in performance of
this particular antenna.
(I am not lumping all VHF & UHF antennas together. I am ONLY talking
about the OSJ).
If you don't have a physical Arrow Antenna OSJ to test with and without
a balun, you don't know what you are talking about.
That goes for computer modeling also. You can't hook up a radio to
computer model.
This antenna works just fine the way it is.

By the way Danny, what is the name of your Antenna Company ?

73 Al Lowe N0IMW Arrow Antenna

On 16 Jun 2005 10:29:02 -0700, "Al" wrote:

I suggest that you would take the time to learn what causes common
mode current to be present on coax transmission line - regardless of
what kind of an antenna it is employed. (For openers I suggest you
start here http://www.w2du.com/r2ch21.pdf )

Then, after getting a grasp on that aspect continue to learn how
common mode current on the transmission line can effect the overall
performance of an antenna's radiation pattern - especially with VHF &
UHF antenna systems then you just might understand what people here
are trying to tell you.

Still others can't seem to understand that effects too small
to measure usually do not matter in the real world.

Others have measured this and reported it to you, but for some reason
you chosen to discount anyone who can show that it disagrees with your
"pet" theory. For me, I've place your theory along with the world is
flat, the moon is made of green cheese, and Iraq has weapons of mass
destruction .

But even for a skeptic, I would thing that the thought of coiling up a
few turns of coax costs very little, definitely won't hurt, and can
only help. Would be sufficient.

Danny, K6MHE

I said I was done with this subject, But ........ I can't take it
anymore.
Again, the Arrow Antenna OSJ Antenna does NOT need a choke balun.
By that I mean it will make no noticeable difference in performance of
this particular antenna.
(I am not lumping all VHF & UHF antennas together. I am ONLY talking
about the OSJ).
If you don't have a physical Arrow Antenna OSJ to test with and without
a balun, you don't know what you are talking about.
That goes for computer modeling also. You can't hook up a radio to
computer model.
This antenna works just fine the way it is.

By the way Danny, what is the name of your Antenna Company ?

73 Al Lowe N0IMW Arrow Antenna

Allen,

My comments were directed to Ed not you, however, can you please
explain to me what is the magical ingredient in your OSJ that makes it
different than any other antenna known to man in that there will be no
common mode current on a coax transmission line when directly
connected to the antenna?

Understand I am not saying your antenna doesn't work - never did say
that. I will say that using a choke at the antenna's feed point will
assure that the antenna will be operating at its best (maximum signal
towards the horizon). By not using a choke can cause an increase to
high angle radiation at the cost of reducing radiation toward the
horizon due to common mode current on the transmission line - just
like any other VHF antenna feed with coax. In other words the antenna
is still radiating the same amount of power, however, much of the your
signal is being wasted in the wrong direction (unless you are talking
to airplanes). For the sake of me I can't fathom why you can not
understand that.

As for you question: I did not claim to own an antenna company. Is
that germane to the subject of the thread?


73
Danny

In article ,
Dan Richardson k6mheat wrote:

Allen,

My comments were directed to Ed not you, however, can you please
explain to me what is the magical ingredient in your OSJ that makes it
different than any other antenna known to man in that there will be no
common mode current on a coax transmission line when directly
connected to the antenna?

May I chime in? Here's my best guess as to the situation with this
antenna:

- Like any other VHF antenna without an effective feedline- decoupling
arrangement and isolation from the mast, it's possible for the
feedline and/or mast to carry some amount of RF current. Quite
simply, there's nothing stopping this from happening.

- The RF impedance of the feedline shield and/or the mast will appear
in parallel with the impedance of the longest (2-meter radiator)
and shortest (440 matching arm) elements on the OSJ.

- What this impedance will be, will be extremely installation-
specific, and so will the currents carried on the feedline braid
and/or mast.

- If the length of these elements to the nearest ground is an odd
multiple of a quarter-wavelength, the low-Z ground will transform
back to a high-Z at the feedpoint, and little unwanted current will
flow. If it's an even number of quarter-wavelengths, the impedance
on the unwanted element will be quite a bit lower - the lower limit
is probably the radiation resistance of a wire of that length. If
it's a nonintegral multiple of a quarter wavelength, the impedance
will be intermediate between these points and will be rather
reactive.

- If the mast is ungrounded at the bottom, the relationships in the
previous paragraph will be reversed - high-Z for even number of
quarter wavelengths, lower (set by radiation resistance) at an odd
number of quarter-wavelengths, reactive in between.

- Since the feedline and mast are likely to be longer than a metre,
any radiation from them is likely to be have strong high-elevation-
angle lobes. Power radiated in these lobes will be less "useful"
in many applications, and since it takes away from the towards-the-
horizon pattern of a theoretically-perfect halfwave radiator it
will reduce the antenna's useful pattern gain by some amount.

So far, I think this is all pretty standard per theory.

Here's where I go out on a limb of speculation:

- In a typical OSJ installation, the feedline and mast are relatively
long, compared to the near-half-wavelength size of the radiator.

- For this reason, if the feedline/mast length happens to be one with
a low and non-reactive RF impedance, its impedance will be a good
deal higher than that of the antenna itself due to the higher
radiation resistance (e.g. 100-200 ohms). Only a relatively small
fraction of the power at the feedpoint will flow into the braid
or mast. As a result, the amount of power "robbed" from the
primary radiator will be small, the high-angle lobes will be weak,
and the reduction in the strength of the towards-the-horizon
primary lobe will be minor.

- If the feedline and/or mast happens to be of a length which results
in a high impedance appearing at the feedpoint, then even less
power will flow on these unwanted elements and the pattern
disruption will be even less.

If the above model and speculation are correct, then two things can
probably be said:

[1] In many installations - perhaps most - the OSJ probably works just
fine without any sort of choking or decoupling arrangement (where I
define "just fine" as "Adding a theoretically-perfect decoupling
arrangement would not result in an improvement in pattern, ERP,
receive sensitivity, etc. which the antenna's owner would notice or
consider worth the trouble."

[2] In some installations, under specific conditions (e.g. short
1/2-wavelength-long feedline) a choke might result in at least
some useful (or at least measureable) improvement in towards-
the-horizon pattern.

I'll finish up by adding a personal observation. As Ed mentioned,
the Arrow OSJ (and/or equivalent antennas made by a local amateur) are
quite popular among members of our city's ARES group. I've measured a
couple of them using an MFJ analyzer, and in my measurements I have
*not* noticed the SWR / measured-impedance to change significantly
when I touch or move the antenna feedline (even when it's a relatively
short 6' piece of RJ58). This suggests to me that (in this case at
least) there's not a lot of RF coming back down the outside of the
feedline to the analyzer case, and that the near-50-ohm impedance
presented by the radiator and matching stubs is the dominant "sink"
for the RF current flow.

Do I think the OSJ is perfect? No - no practical antenna is. If I
were putting one up for a permanent installation, I'd probably
insulate it from the mast, and loop the feedline coax into a choke
balun and/or add a couple of ferrite beads, just because I'm picky and
because the effort to do so is so small.

I would not, however, count on noticing any practical difference in
performance from doing so, and I wouldn't bother doing this in any
sort of temporary or field installation (which is the purpose for
which I keep a break-apart OSJ in my van).

To that extent, I think that Al's statement that the OSJ doesn't need
a choke, is a reasonably fair one. It's not a universal TRVTH but
it's probably a fair, practical rule-of-thumb.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

My comments were directed to Ed not you, however, can you please
explain to me what is the magical ingredient in your OSJ that makes it
different than any other antenna known to man in that there will be no
common mode current on a coax transmission line when directly
connected to the antenna?

I can't believe you are saying ALL antennas are exactly the same !!!

Understand I am not saying your antenna doesn't work - never did say
that. I will say that using a choke at the antenna's feed point will
assure that the antenna will be operating at its best (maximum signal
towards the horizon). By not using a choke can cause an increase to
high angle radiation at the cost of reducing radiation toward the
horizon due to common mode current on the transmission line - =A0just
like any other VHF antenna feed with coax.

There you said it again.

In other words the antenna
is still radiating the same amount of power, however, much of the your
signal is being wasted in the wrong direction (unless you are talking
to airplanes). For the sake of me I can't fathom why you can not
understand that.

No the antenna is NOT perfect. Adding a choke would not make it
perfect.
If it was perfect like you want, I might not be able to make contact
with
cross band repeater on a balloon at 60,000 feet 200 miles away. And
still use a repeater 100 miles away, full quieting with 5 watts.
Check the distance between Denver CO & Cheyenne WY.

Your saying all antennas are the same is like saying all antennas with
a gamma match have a skewed pattern.=20
73 Al Lowe N0IMW

I've measured a
couple of them using an MFJ analyzer, and in my measurements I have
*not* noticed the SWR / measured-impedance to change significantly
when I touch or move the antenna feedline (even when it's a relatively
short 6' piece of RJ58). =A0This suggests to me that (in this case at
least) there's not a lot of RF coming back down the outside of the
feedline to the analyzer case, and that the near-50-ohm impedance
Sniped

Funny how much the comments differ from some one who has a
physical OSJ Antenna and those who just try and model it or
or assume they know it won't work well.
73 Al Lowe N0IMW