wrote:
On 6 Feb 2005 21:19:41 -0800, wrote:

Asymetric array of dipoles
Phased array of vertical monopoles

Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.

I really doubt if you will
supply a link...

www.andrews.com many of those commercial designs could be duplicated
and there are a few repeater builder sites that do exactly that.


???? That's a long distance
telephone service site...


Slick

On 7 Feb 2005 14:06:03 -0800, wrote:

???? That's a long distance
telephone service site...

http://www.andrew.com/products/antennas/

I added an "s" by error. Sheesh.

I figured you'd know their products as they are well known in
broadcast and VHF/UHF ham circles. However that was only one example.
There is also CellOne who also do antenna products and other useful
items. Of course there are only a few hundred (or more) companies
making antennas many of which are suited for a cartiod pattern work.

Allison

wrote:
On 7 Feb 2005 14:06:03 -0800, wrote:

???? That's a long distance
telephone service site...

http://www.andrew.com/products/antennas/

I added an "s" by error. Sheesh.

I figured you'd know their products as they are well known in
broadcast and VHF/UHF ham circles. However that was only one
example.
There is also CellOne who also do antenna products and other useful
items. Of course there are only a few hundred (or more) companies
making antennas many of which are suited for a cartiod pattern work.



I couldn't find anything there that was similar
to this:

http://www.drslick.org/Temp1/yagiplot.jpg


s.

On 7 Feb 2005 21:27:32 -0800, wrote:


I couldn't find anything there that was similar
to this:

http://www.drslick.org/Temp1/yagiplot.jpg

You can lead a horse to water, still can't get it damp.

You'd have to look at the data sheet. All the commercial people
are aware of this and it's accepted practice.

What you missed is a 2 or 4bay dipole is a really nice antenna
that can offer gain and pattern control. The usual use is a 4 bay
vertically oriented with each of the 4 dipoles spaced 90 degrees
around the mast for 5.6db omnidirectional gain. Now, if you want a
directional pattern, such as cartioid then put all four on one side,
also expect slightly higher gain as well. The commercial version are
expensive but are known for their durability but, the good news is
they can be built using copper pipe and will give the same
perfomance. I might add, the gain numbers I gave are not theory,
they are real numbers from proven designs.

Ok, here are some links one how to build it..
http://www.repeater-builder.com/rbti...seddipole.html
some good info here, the metal used is less desirable than
CU pipe. The general design is proven.

http://www.w4dex.com/kc4fwc/ant.htm
Info on making a phasing harness, needed for a 4bay but not
rocket science.

http://dipole.w4zt.com/ look at the plumbers dipole page.
This can be built as a 1/2/4/8 dipole array. The limit is 4
based mostly on size though I've seen one 8 dipole array
and it's long(nearly 45ft!) but very effective. I might add if the
mast pipe is made with 1" copper it can also serve as the supporing
mast. This is a prefered design and offers good all grounded
construction (lightining avoidance and static noise reduction).

The two dipole array with both on one side of the mast is the same
gain as the super jpole with two differences. the 4 bay will be longer
but offers a real gain increase and slightly better pattern control.
The gain increase for this type antenna is predictable, being 3DB
for each time you double the elements. The single being 0 DBd,
2bays 3Dbd, and 4bays 6Dbd . Thereal world the practical antennas
built as omnidirectional are really 0, 2.8 ,5.6dbd due to small but
measureable losses in the cables. If the elements are lined up
on one side the gain is higher (sme claim 9db) with a cartiod
pattern. It's all copper and no required insulators and can be built
more robustly. The pattern is predictable, less is left to chance.
This type of antenna also works well against the side of a metal
building (less tuning difficulties) though you will get a more
directional pattern from the building shielding the opposing
direction. These designs will you get away from theory and use
practical designs.

A repeater group I work with locally used the DBproducts 4bay and
found it the best antenna they've put on the tower to date. It wasn't
cheap and it was heavy. Experience at that site was anything less
robust would barely stand a year before the SWR went to unacceptable.
I've built the 4bay for UHF and it's a solid performer. The all
copper design weathers very well, is very cheap to build
and performs just as well as the commercial versions which are welded
up from aluminum.

I'm sure your getting results from the Jpole but, I can be certain
from using them myself that your results are part luck and can easily
be attributed to the added height (the 70+inches can really help) and
placement more than the presumed gain. If you compare a yagi or
dipole to a J-pole the radiating element must be the same height.
Since the J-pole is really an end fed dipole it has a 38 inch
advantage. For a yagi the centerpoint is the boom.. In direct
comparisons the yagi you built would have to be minimally 3ft higher
to compete on fair ground.

J-poles in general do not like to be near (less than 1/2wave) metalic
structures as it detunes them. Yagi behavour is also sensitive to
metalic structures close to them. The Yo model is not complete
enough for those cases.


Allison
KB1GMX

wrote:
On 7 Feb 2005 21:27:32 -0800, wrote:


I couldn't find anything there that was similar
to this:

http://www.drslick.org/Temp1/yagiplot.jpg

You can lead a horse to water, still can't get it damp.


I would like an H-plane plot, if possible,
and i'm looking for a cardiod pattern, as above,
but with higher dBi if possible.



You'd have to look at the data sheet. All the commercial people
are aware of this and it's accepted practice.

What you missed is a 2 or 4bay dipole is a really nice antenna
that can offer gain and pattern control. The usual use is a 4 bay
vertically oriented with each of the 4 dipoles spaced 90 degrees
around the mast for 5.6db omnidirectional gain. Now, if you want a
directional pattern, such as cartioid then put all four on one side,
also expect slightly higher gain as well. The commercial version are
expensive but are known for their durability but, the good news is
they can be built using copper pipe and will give the same
perfomance. I might add, the gain numbers I gave are not theory,
they are real numbers from proven designs.


2 bays is big and heavy enough! 4 would be
a bit overkill in this situation.



http://dipole.w4zt.com/ look at the plumbers dipole page.
This can be built as a 1/2/4/8 dipole array. The limit is 4


I've tried using an SO-239 attached to the
antenna itself (as they have done here), and it's
a bad idea...pot metal is very weak.



direction. These designs will you get away from theory and use
practical designs.


The theory is close to reality in my case! Except
for the F/B ratio, which seems a bit exaggerated.





A repeater group I work with locally used the DBproducts 4bay and
found it the best antenna they've put on the tower to date. It
wasn't
cheap and it was heavy. Experience at that site was anything less
robust would barely stand a year before the SWR went to unacceptable.
I've built the 4bay for UHF and it's a solid performer. The all
copper design weathers very well, is very cheap to build
and performs just as well as the commercial versions which are welded
up from aluminum.


yeah, but UHF versus VHF is gonna be a huge
difference weight and size wise!



I'm sure your getting results from the Jpole but, I can be certain
from using them myself that your results are part luck and can easily
be attributed to the added height (the 70+inches can really help)
and
placement more than the presumed gain. If you compare a yagi or
dipole to a J-pole the radiating element must be the same height.
Since the J-pole is really an end fed dipole it has a 38 inch
advantage. For a yagi the centerpoint is the boom.. In direct
comparisons the yagi you built would have to be minimally 3ft higher
to compete on fair ground.


The Super J-pole was actually about 5 ft. lower than the
Yagi, so it evened out in the end.


S.

On 8 Feb 2005 11:55:02 -0800, wrote:

I would like an H-plane plot, if possible,
and i'm looking for a cardiod pattern, as above,
but with higher dBi if possible.

Try google, or better yet do a little work. I've already done a fair
bit.

2 bays is big and heavy enough! 4 would be
a bit overkill in this situation.

Not likely.

I've tried using an SO-239 attached to the
antenna itself (as they have done here), and it's
a bad idea...pot metal is very weak.

It's a good idea, use a good connector, most of the quality ones are
nickel or siver plated brass. The ratchack ones are garbage. I
prefer Type N connectors as they are easier to waterproof and good
ones are quite solid.

yeah, but UHF versus VHF is gonna be a huge
difference weight and size wise!

Yep, 3:1. Use light metal. Though using 1/2 inch copper is not as
heavy as it may seem as it's also structural. I have built them for
VHF too.

Of course for 100mhz FM use they do grow a bit and may be too obvious
for a stealth operation.

The rules are simple. Want more signal, put up more metal.

Allison

wrote:


2 bays is big and heavy enough! 4 would be
a bit overkill in this situation.

Not likely.


Definitely! You try putting up a VHF
Super J-pole yourself! You are probably
more used to UHF, so 4 bays doesn't scare
you, but at the broadcast band, you will need
some serious help.

I would love to see what a 4 bay
would do though, but you need serious
bucks to do that, plus alot of manual
labor...




I've tried using an SO-239 attached to the
antenna itself (as they have done here), and it's
a bad idea...pot metal is very weak.

It's a good idea, use a good connector, most of the quality ones are
nickel or siver plated brass. The ratchack ones are garbage. I
prefer Type N connectors as they are easier to waterproof and good
ones are quite solid.


He doesn't explicitely say brass in
his website, and looking at the picture, it
looks like a cheapie SO-239 made of pot metal.

It's a bad idea overall. I would
mount it with 4-40 nuts and bolts on
an aluminum plate, and then attach
that to the antenna.

I've had to take an antenna
down before, just to replace the
broken SO-239 that i used in this
way. Bad idea. You have to make
your antenna very physically strong,
unless you like to spend a lot of time
on your rooftop.



yeah, but UHF versus VHF is gonna be a huge
difference weight and size wise!

Yep, 3:1. Use light metal. Though using 1/2 inch copper is not as
heavy as it may seem as it's also structural. I have built them for
VHF too.


1/2" copper gets heavy with 2 bays, trust me.

Especially for something like the Super J.





The rules are simple. Want more signal, put up more metal.


Or want more ERP, or a lower angle
of radiation, put up more metal.

I would agree.



Slick