Hm, why is that? How does an open stub prevent coupling from the antenna
to the feedline?

Roy Lewallen, W7EL

Al wrote:
Hello, Roy & the Group.

One think you may have missed, the original post was about a Arrow
Antenna J-Pole. This is an Open Stub type J-Pole, Not a Closed Stub
type like the copper pipe ones. The OSJ does not need a choke, it does
not have a problem with feedline radiation or a problem with Common
Mode Currents.


In the typical J-pole antenna, the shield connects to the long element
and the center to the stub. �I don't know your antenna in particular,
but I would suspect this is the case and don't believe it is considered
a radiating element.


The OSJ is not a typical J-pole.

73 Al Lowe N0IMW Arrow Antenna

Hm, why is that? How does an open stub prevent coupling from the antenna
to the feedline?

Roy Lewallen, W7EL

I was hoping we would not have to go through this AGAIN.

The typical J-Pole (Closed Stub) was designed to feed with open feed
line. Because Hams insist on feeding it with coax, a Band-Aid is
needed to choke off feed line radiation & common mode currents.
The Open Stub J-Pole was designed to feed with coax. So it don't need
the Band Aid.
The difference between the two is discussed in several antenna books.
Just ask anyone the owns one.
(http://www.eham.net/reviews/detail/1613)
Besides your the antenna expert, tell us why it would.
73 Al Lowe N0IMW

I was hoping we would not have to go through this AGAIN.

The typical J-Pole (Closed Stub) was designed to feed with open feed
line. Because Hams insist on feeding it with coax, a Band-Aid is
needed to choke off feed line radiation & common mode currents.
The Open Stub J-Pole was designed to feed with coax. So it don't need
the Band Aid.
The difference between the two is discussed in several antenna books.
Just ask anyone the owns one.
(http://www.eham.net/reviews/detail/1613)
Besides your the antenna expert, tell us why it would.
73 Al Lowe N0IMW

For exactly the same reason that you need a choke on a ground plane or
any other antenna feed with coax. Depending upon the length of the
feed line common mode current can be substantial. This, in turn,
increases higher angle radiation. Now if you are most interested in
talking to airplanes that would be a good thing, but if you prefer
maximum signal towards the horizon then put a choke on that sucker!

Danny, K6MHE

Dan:

Some of these arguments carry on into the realm where I lose interest...
but right on when you say, "...put a choke on that sucker!"

This may be due to the fact that I am not an "antenna guru" and can't be
certain when one is best, and when not... so what? Make fun of me
then!!!
tongue-sticking-out-grin

Warmest regards,
John

"Dan Richardson arrl net" k6mheatdot wrote in message
...


I was hoping we would not have to go through this AGAIN.

The typical J-Pole (Closed Stub) was designed to feed with open feed
line. Because Hams insist on feeding it with coax, a Band-Aid is
needed to choke off feed line radiation & common mode currents.
The Open Stub J-Pole was designed to feed with coax. So it don't need
the Band Aid.
The difference between the two is discussed in several antenna books.
Just ask anyone the owns one.
(http://www.eham.net/reviews/detail/1613)
Besides your the antenna expert, tell us why it would.
73 Al Lowe N0IMW

For exactly the same reason that you need a choke on a ground plane or
any other antenna feed with coax. Depending upon the length of the
feed line common mode current can be substantial. This, in turn,
increases higher angle radiation. Now if you are most interested in
talking to airplanes that would be a good thing, but if you prefer
maximum signal towards the horizon then put a choke on that sucker!

Danny, K6MHE

They who discuss "power radiated from the feedline", yet are unable to
measure (in watts) or calculate (in watts) the MAGNITUDE of the
effect, belong to a set of waffling old wives.

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.

Do we always, without valid reason, just copy the practical
construction details from ARRL handbooks, on the grounds that if it
once worked OK for somebody else it might work for me.

But of course, you'll never get to know, having copied a very simple
system which contains a choke, unless you remove the choke and observe
what happens to system performance. Or alternatively, add a choke if
the ARRL handbook implies that you don't need one, and then make more
observations.

My guess is that in many cases hardly anything will happen or be
noticed. Simply because the MAGNITUDE of the effects due to line
radiation is too small to be of consequence or detected even.

If you can't measure or calculate the MAGNITUDE of the effects, stop
worrying about it.

The frequency at which "radiation from the line" is mentioned in this
newsgroup is out of all proportion to its importance. There's a
tendency to drag it into the discussion because it is the last of the
few remaining technical topics available to argue about. You have at
least heard about the subject in the magazines.

The very last, of course, will be SWR. Because there is a meter which
supposedly measures it but doesn't. And it is difficult to argue
against meter users, such as Bird, suffering from delusions of
accuracy, who are invariably convinced they are right.
----
Reg, G4FGQ

Reg Edwards wrote:
If you can't measure or calculate the MAGNITUDE of the effects, stop
worrying about it.

Does RF burns on my lip count as a measurement? :-)
--
73, Cecil http://www.qsl.net/w5dxp

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Reg Edwards wrote:
If you can't measure or calculate the MAGNITUDE of the effects,
stop
worrying about it.

Does RF burns on my lip count as a measurement? :-)

=============================

Not unless your yelp indicated how may watts the microphone was
radiating at the time. ;o)
---
Reg

Reg Edwards wrote:

They who discuss "power radiated from the feedline", yet are unable to
measure (in watts) or calculate (in watts) the MAGNITUDE of the
effect, belong to a set of waffling old wives.


Those who take no precautions to prevent their feedline from becoming
part of the antenna, belong to a set of people who don't even know what
their antenna IS.

There's a part you call "the antenna", and another part you call "the
feedline". Wishful thinking will not stop RF current from flowing
directly from one to the other.

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.

Try a clamp-on RF current meter, a little modeling... or even a little
common sense.

There's a place called "the feedpoint" where the antenna and the
feedline are connected directly together. Might that be a good location
for a choke to keep them separate? Yes, it almost certainly would.

Chokes may also be needed at other locations, but it's hard to justify
anywhere else as your *first* choice. (The exception is the Carolina
Windom and similar antennas where part of the feedline is intended to
radiate. But even there, they put a good choke at the point where they
want RF currents on the feedline to stop.)

Queen Elizabeth 1 of England had the good sense to take a bath every six
months "whether I need it or not". If you don't know whether your
feedline smells of RF, then follow her excellent advice and use a
choke.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian, not wishing to be classed amongst the old wives you have very
carefully avoided talking about "power radiated from feedlines". You
have shifted to using clamp-on ammeters.

But people who DO discuss things in such terms are unable to justify
the use of chokes by quantifying the power actually radiated and
setting limits on what power level is acceptable or is not acceptable.
If they can't measure or calculate the power level then they know
nothing about what they are are talking.

Refer to what Lord Kelvin said about measurements.

Can you suggest an acceptable level of amps as measured on a clamp-on
ammeter?
----
Reg, G4FGQ

----------------------------------------------------------------------
---------


"Ian White GM3SEK" wrote in message
...
Reg Edwards wrote:

They who discuss "power radiated from the feedline", yet are unable
to
measure (in watts) or calculate (in watts) the MAGNITUDE of the
effect, belong to a set of waffling old wives.


Those who take no precautions to prevent their feedline from
becoming
part of the antenna, belong to a set of people who don't even know
what
their antenna IS.

There's a part you call "the antenna", and another part you call
"the
feedline". Wishful thinking will not stop RF current from flowing
directly from one to the other.

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.

Try a clamp-on RF current meter, a little modeling... or even a
little
common sense.

There's a place called "the feedpoint" where the antenna and the
feedline are connected directly together. Might that be a good
location
for a choke to keep them separate? Yes, it almost certainly would.

Chokes may also be needed at other locations, but it's hard to
justify
anywhere else as your *first* choice. (The exception is the Carolina
Windom and similar antennas where part of the feedline is intended
to
radiate. But even there, they put a good choke at the point where
they
want RF currents on the feedline to stop.)

Queen Elizabeth 1 of England had the good sense to take a bath every
six
months "whether I need it or not". If you don't know whether your
feedline smells of RF, then follow her excellent advice and use a
choke.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

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