I built a so called "Super J-pole" which is really two stacked
collinear half
wave antennas with a quarter wave phasing stub between them. The
design is by
N7QVC and it can be seen at http://www.n7qvc.com/amateur_radio/
copper.html. I
also placed a photograph of a representative build in the photo
section of this
reflector at
http://groups.yahoo.com/group/amateu...um/1449680574/
pic/3362107\
0/view?picmode=&mode=tn&order=ordinal&start=1&count= 20&dir=asc.

I have had good results with this antenna but I wanted to make it into
a dual
band antenna that would work on seventy centimeters as well as on two
meters. I
was wondering if I could use a technique developed by Edison Fong,
WB6IQN on
this antenna in the same way he used it on an ordinary single half
wave J-pole.
What he did is to place an open quarter wave stub at the top of the
two half
wave lengths for seventy centimeters. That stub limits the UHF signal
to the
two half waves length at UHF of the antenna. It seems like it would
work from
having read his paper on the combination two meter and seventy
centimeter J-pole
antenna. That would give the antenna the same gain on seventy
centimeters as a
J-pole that is just for that band. For reference I have placed WB6IQNs
paper in
the files section of the newsgroup at
http://f1.grp.yahoofs.com/v1/
kL6QTZLk1DQjM_Cn3vuvnsLUIuEsvRHSqUZyX2mw294a7mYKkc \
FBIXXlRY_6QxreqNWVpn0b7Dogiw9LafU63W429yoO/DBJ2_port_art.pdf.

My first question is does anyone see any reason why this would not
work?

My second question is how would I construct the stub into a copper J-
pole.
Since WB6IQNs J-pole is a wire antenna, with or without a plastic
radome, he
used a piece of Coaxial cable as part of his two meter wire with the
shield at
the end of the seventy centimeter portion of the antenna shorted to
the two
meter radiator and the bottom of the shield, which is a quarter wave
at UHF
below the top of the UHF segment, open relative to the two meter
radiator.
Could I just use a full quarter wave stub made from a copper T, a
street L, and
a short length of copper pipe turned back down along the two meter
radiator? (A
street L is a ninety degree bend formed to allow it to be close
coupled to an
adjacent fitting without a pipe nipple in between.)

My third question is if instead of shortening the lower VHF half wave
electrically to a UHF length I found a way to short out the quarter
wave phasing
stub between the two VHF half wave radiators to UHF signals thus
giving UHF
signals three full wave lengths of radiator to use would the gain be
worth the
effort. To provide the shunting of the VHF quarter wave phasing stub I
was
GUESSING that a half wave UHF coupling stub might work.

I freely admit to being out of my depth; or as a mariner might say off
my
soundings; here. So I'm fully prepared to hear that the UHF half wave
coupling
stub would not work as a shunt for the UHF signals to get past the VHF
quarter
wave phasing stub. I have no pretense to any expertise. I'm trying to
learn.
Laugh all you want but if it won't work please tell me in neophyte
decipherable
language why not. If you have any guidance to offer it would be most
welcome
but please keep the fog index down to the degree you are able. Thank
you in
advance.

--
Tom Horne, W3TDH

On Mon, 28 Mar 2011 11:29:25 -0700 (PDT), Tom Horne
wrote:

please keep the fog index down to the degree you are able

Hi Tom,

After looking at the mile long URL to one of your offerings - I would
like to see the fog lift too.

Why don't you simply tell us what performance you want to achieve from
an antenna?

A simple quarterwave antenna built on a SO-239 connector with four
drooping radials is squat simple, cheap, and can be built and trimmed
to near perfect match in half an hour or less. You want multiband?
Make two vertical, slightly skewed elements (each cut for the suited
band) joined at the feedpoint. You want more gain? How much more?
Build two or (n-times) more and spend your effort in learning to
construct feedline systems to additively join them.

73's
Richard Clark, KB7QHC

On Mar 30, 2:09*am, Richard Clark wrote:
On Mon, 28 Mar 2011 11:29:25 -0700 (PDT), Tom Horne

wrote:
please keep the fog index down to the degree you are able

Hi Tom,

After looking at the mile long URL to one of your offerings - I would
like to see the fog lift too.

Why don't you simply tell us what performance you want to achieve from
an antenna?

A simple quarterwave antenna built on a SO-239 connector with four
drooping radials is squat simple, cheap, and can be built and trimmed
to near perfect match in half an hour or less. *You want multiband?
Make two vertical, slightly skewed elements (each cut for the suited
band) joined at the feedpoint. *You want more gain? *How much more?
Build two or (n-times) more and spend your effort in learning to
construct feedline systems to additively join them.

73's
Richard Clark, KB7QHC

Richard
I wanted to explore whether it is practical to have my collinear dual
half wave J-pole serve as a dual band antenna. If it were practical I
would want the same gain on seventy centimeters that I have been
getting out of the dual stacked half wave on two meters. The
available testing that I was able to find says that it is 6 DB over a
quarter wave vertical. What I would happily settle for would be for
it to have the same gain on seventy centimeters as the dual band
simple J-pole I am using now. After talking to Rol Anders, K3RA; who
was the instructor for my Extra theory class and is the present
chairman of the Question Pool Committee of the National Council of
Volunteer Examiner Coordinators (NCVEC); last night I am taking that
later approach. That is the approach that I outlined in the first
paragraph of just putting an open blocking stub for UHF at thirty five
centimeters ~ up the lower two meter half wave and therefore below the
two meter phasing stub between the two meter half wave segments. That
has the virtue of being simple and still giving me a dual band antenna
that has better gain on UHF then the unmodified two meter antenna
would.

I wanted a dual band antenna because I only have three suitable
mounting points on my home and I already have plans for a six meter J-
pole and an anemometer / sensor array assembly on the other two. I
have an Arrow dual band J-pole up on that mounting point right now but
I wanted to return to the higher gain of the collinear dual half wave
J-pole that gave me so much better real world performance on two
meters. It is my hope that just adding the seventy centimeter band
blocking stub to the collinear antenna's lower two meter half wave
segment will do the trick.

--
Tom Horne, W3TDH

On Wed, 30 Mar 2011 10:23:51 -0700 (PDT), Tom Horne
wrote:

Richard
I wanted to explore whether it is practical to have my collinear dual
half wave J-pole serve as a dual band antenna. If it were practical I
would want the same gain on seventy centimeters that I have been
getting out of the dual stacked half wave on two meters.

Which would be quite horrible.

The
available testing that I was able to find says that it is 6 DB over a
quarter wave vertical. What I would happily settle for would be for
it to have the same gain on seventy centimeters as the dual band
simple J-pole I am using now.

Hi Tom,

It is extremely hard to accept claims for J-Poles when nothing is said
about the care in choking the feed point, and further choking the
section of line a quarter wave away from the feed point.

Typically this discussion is arrived at with some surprise on the part
of the J-Pole user who posts here (I know you have participated here
before, and are thus not a newbie). Some (which means too many)
respond that choking is unnecessary. They are satisfied with its
performance (never daring to examine that it could be vastly
improved).

We also have writers here who condemn the J-Pole vehemently in equal
measure. They, too, have not examined the necessity of choking and
they suffer from the knowledge that things could be vastly improved.

This is the pitiable lament of feeding halfwave elements in any form.

Let's examine what you call "available testing." I presume this means
in software, and not in the lab (never mind alternatives such as out
in a field). I could be wrong and you may correct this on your
response.

However, moving on with whatever presumption, the reason why choking
is important is that with High Z antennas, they tend to drive the
transmission line into radiation. This extends the length of the
radiator, and too often this raises the lobe of maximum radiation up
into the sky (you are very near that with the half wave where 5/8ths
is considered the limit of physical height before this trips over).

These are all issues related to a vertical, and its elevation goes
into the mix too to further confuse comparisons.

Now, basically you are asking the same antenna to operate at roughly
triple the frequency. This also means either element of the native
radiator will stand like something under 3/2 wavelengths tall - truly
a cloud burner (not good).

You speak of stubs to fix this. You would have to start with two 3/2
halfwave radiators, one over the other. Fixing the phase for both 2M
and 440 would be a miracle in achievement. I presume you would also
trap the individual 3/2 wave length sections into two 5/8ths (but the
ratios don't quite work out that way); or three half waves; or six
quarter waves - and then do it again for the section above. Whew!

This is a monumental task - but you have simpler goals as the
following would suggest:

just putting an open blocking stub for UHF at thirty five
centimeters ~ up the lower two meter half wave and therefore below the
two meter phasing stub between the two meter half wave segments. That
has the virtue of being simple and still giving me a dual band antenna
that has better gain on UHF then the unmodified two meter antenna
would.

The blocking stub I presume you to mean a trap for 440. It is going
to upset the matching stub between the two halfwave 2M elements. Here
you will have to juggle between tuning them both on each band.

It is less than monumental, but still quite a job, and one that
demands that you cut and try and fully erecting your last attempt to
see how it works (doing this on the ground is going to lead to grief -
especially if you ignore proper choking).

73's
Richard Clark, KB7QHC

On 3/30/2011 12:23 PM, Tom Horne wrote:

Richard
I wanted to explore whether it is practical to have my collinear dual
half wave J-pole serve as a dual band antenna. If it were practical I
would want the same gain on seventy centimeters that I have been
getting out of the dual stacked half wave on two meters. The
available testing that I was able to find says that it is 6 DB over a
quarter wave vertical. What I would happily settle for would be for
it to have the same gain on seventy centimeters as the dual band
simple J-pole I am using now. After talking to Rol Anders, K3RA; who
was the instructor for my Extra theory class and is the present
chairman of the Question Pool Committee of the National Council of
Volunteer Examiner Coordinators (NCVEC); last night I am taking that
later approach. That is the approach that I outlined in the first
paragraph of just putting an open blocking stub for UHF at thirty five
centimeters ~ up the lower two meter half wave and therefore below the
two meter phasing stub between the two meter half wave segments. That
has the virtue of being simple and still giving me a dual band antenna
that has better gain on UHF then the unmodified two meter antenna
would.

I wanted a dual band antenna because I only have three suitable
mounting points on my home and I already have plans for a six meter J-
pole and an anemometer / sensor array assembly on the other two. I
have an Arrow dual band J-pole up on that mounting point right now but
I wanted to return to the higher gain of the collinear dual half wave
J-pole that gave me so much better real world performance on two
meters. It is my hope that just adding the seventy centimeter band
blocking stub to the collinear antenna's lower two meter half wave
segment will do the trick.

--
Tom Horne, W3TDH

http://www.arrowantenna.info/osj/j-pole.html

This design works moderately well. Drive the 19.25 inch element. The
51 inch element is the radiator on 2m, the 6.xx inch element makes the
19.25 inch one radiate on 440. The thing isn't great on 440 because the
51 inch portion is there. It is rugged though.

I built a duplicate, which you can do if you look at all the parts pages
on the site. The main problem, same as all J poles, is common mode
current issues on the feedline.

tom
K0TAR

On 3/31/2011 6:43 PM, tom wrote:
On 3/30/2011 12:23 PM, Tom Horne wrote:

Richard
I wanted to explore whether it is practical to have my collinear dual
half wave J-pole serve as a dual band antenna. If it were practical I
would want the same gain on seventy centimeters that I have been
getting out of the dual stacked half wave on two meters. The
available testing that I was able to find says that it is 6 DB over a
quarter wave vertical. What I would happily settle for would be for
it to have the same gain on seventy centimeters as the dual band
simple J-pole I am using now. After talking to Rol Anders, K3RA; who
was the instructor for my Extra theory class and is the present
chairman of the Question Pool Committee of the National Council of
Volunteer Examiner Coordinators (NCVEC); last night I am taking that
later approach. That is the approach that I outlined in the first
paragraph of just putting an open blocking stub for UHF at thirty five
centimeters ~ up the lower two meter half wave and therefore below the
two meter phasing stub between the two meter half wave segments. That
has the virtue of being simple and still giving me a dual band antenna
that has better gain on UHF then the unmodified two meter antenna
would.

I wanted a dual band antenna because I only have three suitable
mounting points on my home and I already have plans for a six meter J-
pole and an anemometer / sensor array assembly on the other two. I
have an Arrow dual band J-pole up on that mounting point right now but
I wanted to return to the higher gain of the collinear dual half wave
J-pole that gave me so much better real world performance on two
meters. It is my hope that just adding the seventy centimeter band
blocking stub to the collinear antenna's lower two meter half wave
segment will do the trick.

--
Tom Horne, W3TDH

http://www.arrowantenna.info/osj/j-pole.html

This design works moderately well. Drive the 19.25 inch element. The 51
inch element is the radiator on 2m, the 6.xx inch element makes the
19.25 inch one radiate on 440. The thing isn't great on 440 because the
51 inch portion is there. It is rugged though.

I built a duplicate, which you can do if you look at all the parts pages
on the site. The main problem, same as all J poles, is common mode
current issues on the feedline.

tom
K0TAR

Sorry, missed the part where you already have this antenna. My fault
for not reading the whole post until after I responded.

tom
K0TAR

On Thu, 31 Mar 2011 18:46:22 -0500, tom wrote:

http://www.arrowantenna.info/osj/j-pole.html

This design works moderately well. Drive the 19.25 inch element. The 51
inch element is the radiator on 2m, the 6.xx inch element makes the
19.25 inch one radiate on 440. The thing isn't great on 440 because the
51 inch portion is there. It is rugged though.

I built a duplicate, which you can do if you look at all the parts pages
on the site. The main problem, same as all J poles, is common mode
current issues on the feedline.

tom
K0TAR

Sorry, missed the part where you already have this antenna. My fault
for not reading the whole post until after I responded.

Hi Tom,

Your suggestion would have been my choice too - except for Tom's first
purchase choice. The open stub has always seemed to be a more natural
feed method.

The addition of the parasitic radiator is still an option for any
design.

73's
Richard Clark, KB7QHC

On Apr 1, 1:34*am, Richard Clark wrote:
On Thu, 31 Mar 2011 18:46:22 -0500, tom wrote:
http://www.arrowantenna.info/osj/j-pole.html

This design works moderately well. Drive the 19.25 inch element. The 51
inch element is the radiator on 2m, the 6.xx inch element makes the
19.25 inch one radiate on 440. The thing isn't great on 440 because the
51 inch portion is there. It is rugged though.

I built a duplicate, which you can do if you look at all the parts pages
on the site. The main problem, same as all J poles, is common mode
current issues on the feedline.

tom
K0TAR

Sorry, missed the part where you already have this antenna. *My fault
for not reading the whole post until after I responded.

Hi Tom,

Your suggestion would have been my choice too - except for Tom's first
purchase choice. *The open stub has always seemed to be a more natural
feed method.

The addition of the parasitic radiator is still an option for any
design. *

73's
Richard Clark, KB7QHC

Richard
I didn't ignore choking the feed line but I will readily confess that
I did not choke it twice. Starting immediately below the bottom of
the matching stub I followed the recommendation of the various authors
and wound a multi-turn coax balun with a six inch diameter coils of
coax. They call for ten turns if I recall correctly. I was not aware
of the need for a second choke at one quarter wavelength away. Do you
have the energy to explain why that is necessary? How critical is the
length between the two chokes. Do I use the middle of the two chokes
as my measuring points? Could I substitute a one to one current balun
built of ferrite beads? That would have a less intrusive appearance
and accumulate less ice in the winter.
If you check the link that I gave for Ed Fong's dual band j-pole;
available here
http://f1.grp.yahoofs.com/v1/
kL6QTZLk1DQjM_Cn3vuvnsLUIuEsvRHSqUZyX2mw294a7mYKkc
\FBIXXlRY_6QxreqNWVpn0b7Dogiw9LafU63W429yoO/DBJ2_port_art.pdf or just
look it up in the files section of the Yahoo reflector; you will see
that he did test it in the field with fairly sophisticated
instrumentation. He uses a trapped radiator to obtain similar gain on
seventy centimeters as a simple J-pole without the trap gets on two
meters. His work was published in QST and I didn't find any
authoritative repudiation, or even strong criticism, of his design.
Why would the presence of the trap in the lower half wave of the two
meter collinear half wave J-pole wreck the tuning on two meters.

I'm only trying to learn here.
--
Tom Horne, W3TDH

On Sat, 2 Apr 2011 12:06:16 -0700 (PDT), Tom Horne
wrote:

Richard
I didn't ignore choking the feed line but I will readily confess that
I did not choke it twice. Starting immediately below the bottom of
the matching stub I followed the recommendation of the various authors
and wound a multi-turn coax balun with a six inch diameter coils of
coax. They call for ten turns if I recall correctly.

Hi Tom,

This sound like very common advice - so common that it begs
investigation because it is common advice for HF Choking, not 2M, and
certainly not 70cm. However, this common advice acknowledges the need
for choking.

You would be better served using ferrites (W2DU style BalUn/Choke),
or, if you really wish to stick with wound coax, then use a Grid Dip
Meter to test its resonance (which should reveal you can't serve both
bands). Using an antenna analyzer to do this will give you measurable
Z, and that may give you the data to see how well you are doing. You
may wind a lot of chokes to discover that the diameter is
extraordinarily huge (or so the same for turn count - one or the other
or both).

I was not aware
of the need for a second choke at one quarter wavelength away. Do you
have the energy to explain why that is necessary?

[Do I have the energy.... With all the junk cluttering this space
outside of this thread, I have plenty of energy.]

The antenna fields will try to excite the transmission line's common
mode (the shield of the coax that it sees). This will induce currents
that will become radiative (just like stacked elements in a vertical
multi-element radiator - sound familiar?). The use of chokes at
quarterwave intervals snubs these currents.

Sometimes more chokes are needed. I use a 20' long line with a bead
every four inches or so. The intent is to create a very long resistor
(very wide bandwidth) with very short leads (very high frequency)
between its distributed resistance.

How critical is the
length between the two chokes.

Not particularly, you would be well served to attempt to make it at
the interval of quarterwave at the highest frequency used (70cm).
This, then, would snub lower frequency (2M) common mode currents.

Do I use the middle of the two chokes
as my measuring points?

This sounds deceptively exact (and probably a consideration for those
enormous chokes of common advice vintage). No, such exactitude is
going to be lost at the 70cm scale anyway which will be perturbed by
other factors (have I talked about environment?).

Could I substitute a one to one current balun
built of ferrite beads? That would have a less intrusive appearance
and accumulate less ice in the winter.
If you check the link that I gave for Ed Fong's dual band j-pole;
available here
http://f1.grp.yahoofs.com/v1/
kL6QTZLk1DQjM_Cn3vuvnsLUIuEsvRHSqUZyX2mw294a7mYKk c
\FBIXXlRY_6QxreqNWVpn0b7Dogiw9LafU63W429yoO/DBJ2_port_art.pdf or just
look it up in the files section of the Yahoo reflector;

I would prefer not to add yet one more account registration to simply
view this, sorry. However, the narrative here should tell you if we
agree.

you will see
that he did test it in the field with fairly sophisticated
instrumentation. He uses a trapped radiator to obtain similar gain on
seventy centimeters as a simple J-pole without the trap gets on two
meters.

My background was working in the standards laboratory system of NBS
(my speciality was RF measurement to the highest accuracies). I know
that sophisticated instrumentation and quality results don't
necessarily track each other. My point was about environment, not
instrumentation anyway. You don't need $1000 meters, but you might
need $1,000,000 environment.

The description of Apple's echoless environmental chamber used to test
their iPod is a marvel of engineering, and cost a stack of dollars.

His work was published in QST and I didn't find any
authoritative repudiation, or even strong criticism, of his design.

The same could be said of publishing it in Playboy. QST needs content
to offer subscribers. Vanity articles satisfy that need. Think of
these articles as the introduction to a topic, not the final word.

Why would the presence of the trap in the lower half wave of the two
meter collinear half wave J-pole wreck the tuning on two meters.

The trap's tuning is heavily influenced by the geometry of the
elements because they are also part of the tuning. The trap disturbs
that symmetry. You have also introduced new L and C components that
further upsets the total circuit. These things are not super-critical
when you consider that moving a resonance (say) 145KHz out of 145MHz
is only a shift of 0.1%. That isn't super-critical either.

Or maybe it is.

I'm only trying to learn here.

Let me know if this helps.

73's
Richard Clark, KB7QHC

On Sat, 02 Apr 2011 16:04:27 -0700, Richard Clark
wrote:

On Sat, 2 Apr 2011 12:06:16 -0700 (PDT), Tom Horne
wrote:

Richard
I didn't ignore choking the feed line but I will readily confess that
I did not choke it twice. Starting immediately below the bottom of
the matching stub I followed the recommendation of the various authors
and wound a multi-turn coax balun with a six inch diameter coils of
coax. They call for ten turns if I recall correctly.

Hi Tom,

This sound like very common advice - so common that it begs
investigation because it is common advice for HF Choking, not 2M, and
certainly not 70cm. However, this common advice acknowledges the need
for choking.

You would be better served using ferrites (W2DU style BalUn/Choke),
or, if you really wish to stick with wound coax, then use a Grid Dip
Meter to test its resonance (which should reveal you can't serve both
bands). Using an antenna analyzer to do this will give you measurable
Z, and that may give you the data to see how well you are doing. You
may wind a lot of chokes to discover that the diameter is
extraordinarily huge (or so the same for turn count - one or the other
or both).

This thread has shown me that I don't know enough about Common Mode
Chokes. I think they might also be referred to as transmission line
chokes.

What I need to know is
1- When to use them. RF in the Shack is pretty obvious
2- When not to use them. There must be some negatives.
3- "Compare and Contrast" the Inductor-capacitor choke with the
Ferrite Choke(W2DU). Are they electrically equivalent?
4- Are either of them a multi band solution?
5- Are there Upper and lower frequency limitations for using them.


As usual, a Google search provides an overwhelming set of responses
that most likely will cover the subject in greater detail than I can
digest.

Early in the list provided by the search I discovered
http://www.audiosystemsgroup.com/RFI-Ham.pdf

That may have all the answers but I have only glanced at the beginning
of the 66 page document.

John Ferrell W8CCW