UHF Yagi Ant construction Question
 

Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector and
directors are all connected from an electric point of view?

Cheers,
Xanax.


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I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector and
directors are all connected from an electric point of view?

Provided the lengths are corrected for the boom (connected or not connected)
there is no differance in the antenna. It might make some differance if the
connection is not 100% all the time as the elements could become loose and
not be connected . YOu can get all kinds of noise on signals if the
elements become loose. That is one plus for insulating the elements.
Unless welded to the boom many elements will loosen up some in time.

The answer would be probably, but you really need to give more
information such as

o frequency
o boom diameter and shape
o description of the clamp

Draw us a picture with words.

tom
K0TAR

Xanax wrote:

Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector and
directors are all connected from an electric point of view?

Cheers,
Xanax.


---
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The boom is 3 side square aluminium tubing as used in construction of
Aluminium doors and windows etc..

The elements are attached to the boom but U bolts that are fasened very very
tightly. It's up for about 6 months now and I check it every month and there
isn't any loose ness at all.

Cheers,
Xanax.
"Tom Ring" wrote in message
...
The answer would be probably, but you really need to give more information
such as

o frequency
o boom diameter and shape
o description of the clamp

Draw us a picture with words.

tom
K0TAR

Xanax wrote:

Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector
and directors are all connected from an electric point of view?

Cheers,
Xanax.


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.682 / Virus Database: 444 - Release Date: 11/05/2004



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Ok, fine. The frequency and size of the U channel are still needed.

Also, how are the U bolts fastening the bits together? I can think of
at least 2 ways to do it with what you've described. 1 - the U bolts
are pinning the element like a staple pins a wire, and 1 or 2 of them
could be used in that case. 2 - the elements are large enough diameter
and the U bolts small enough that the U bolts pass around the boom, and
through holes drilled in the elements. I suspect #2 is unlikely at UHF,
though.

Also what is the orientation of the channel to the elements?

tom
K0TAR

Xanax wrote:

The boom is 3 side square aluminium tubing as used in construction of
Aluminium doors and windows etc..

The elements are attached to the boom but U bolts that are fasened very very
tightly. It's up for about 6 months now and I check it every month and there
isn't any loose ness at all.

Cheers,
Xanax.
"Tom Ring" wrote in message
...

The answer would be probably, but you really need to give more information
such as

o frequency
o boom diameter and shape
o description of the clamp

Draw us a picture with words.

tom
K0TAR

Xanax wrote:


Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector
and directors are all connected from an electric point of view?

Cheers,
Xanax.


---
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Version: 6.0.682 / Virus Database: 444 - Release Date: 11/05/2004



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"Xanax" wrote in message ...
Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector and
directors are all connected from an electric point of view?

Cheers,
Xanax.

No. The driven element can be grounded to the boom also. Again, no
change, except you add a matching device. The connection is at the
high current/min voltage point. Being there is little voltage at the
center of the 1/2 wave elements, the boom is pretty much ignored by
the antenna. Also, it's at a 90 degree angle, which further reduces
coupling to the elements. My cushcraft tri-band beam uses an insulated
driven element, but most of the yagi's I build have all the elements
grounded to the boom. My three el 6m yagi has all the elements welded
to the boom, and the whole antenna, elements, boom, even the gamma
match tube, are all hard copper tubing. It's a one piece antenna. Or a
plumbers delight, as many call that method of construction... MK

Hmm. Based on your response, I bet I misunderstood the question. Been
working on finding element corrections for 432 this week.

tom
K0TAR

Mark Keith wrote:

"Xanax" wrote in message ...

Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector and
directors are all connected from an electric point of view?

Cheers,
Xanax.


No. The driven element can be grounded to the boom also. Again, no
change, except you add a matching device. The connection is at the
high current/min voltage point. Being there is little voltage at the
center of the 1/2 wave elements, the boom is pretty much ignored by
the antenna. Also, it's at a 90 degree angle, which further reduces
coupling to the elements. My cushcraft tri-band beam uses an insulated
driven element, but most of the yagi's I build have all the elements
grounded to the boom. My three el 6m yagi has all the elements welded
to the boom, and the whole antenna, elements, boom, even the gamma
match tube, are all hard copper tubing. It's a one piece antenna. Or a
plumbers delight, as many call that method of construction... MK

thats great on the info.
I'm pretty sure I have it right then.
cheeers
xanax
"Tom Ring" wrote in message
...
Hmm. Based on your response, I bet I misunderstood the question. Been
working on finding element corrections for 432 this week.

tom
K0TAR

Mark Keith wrote:

"Xanax" wrote in message
...

Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector
and directors are all connected from an electric point of view?

Cheers,
Xanax.


No. The driven element can be grounded to the boom also. Again, no
change, except you add a matching device. The connection is at the
high current/min voltage point. Being there is little voltage at the
center of the 1/2 wave elements, the boom is pretty much ignored by
the antenna. Also, it's at a 90 degree angle, which further reduces
coupling to the elements. My cushcraft tri-band beam uses an insulated
driven element, but most of the yagi's I build have all the elements
grounded to the boom. My three el 6m yagi has all the elements welded
to the boom, and the whole antenna, elements, boom, even the gamma
match tube, are all hard copper tubing. It's a one piece antenna. Or a
plumbers delight, as many call that method of construction... MK



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Well, as long as the design matches your construction technique and
boom. ;) If not, it may be far from working well.

VHF and up yagis have to be made just as specified in construction
articles, including element diameter and taper, element mounting method,
and boom diameter. If not, they can end up performing quite differently
than what you would expect.

The higher the frequency, the more critical things become. At 432, for
instance, we use a length tolerance of .5mm or better on element length.
Cut to just a bit too long, and then carefully file to length. Then
chamfer the tips.

We were picky, because we were making EME antennas for arrays, and very
long boom test antennas for antenna range competitions.

And a hint on old VHF/UHF yagis - Scothbrite the elements after you test
the antenna and test it again. We found it worth about .4dB on an
antenna only 2 years old.

tom
K0TAR

Xanax wrote:

thats great on the info.
I'm pretty sure I have it right then.
cheeers
xanax
"Tom Ring" wrote in message
...

Hmm. Based on your response, I bet I misunderstood the question. Been
working on finding element corrections for 432 this week.

tom
K0TAR

Mark Keith wrote:


"Xanax" wrote in message
...


Hi all,
I have a uhf yagi uda antenna mounted on the roof I have all the element
(alu welding rods) clamped to a alu- boom except the active elements.
Does this effect the preformance of the antenna in that the reflector
and directors are all connected from an electric point of view?

Cheers,
Xanax.


No. The driven element can be grounded to the boom also. Again, no
change, except you add a matching device. The connection is at the
high current/min voltage point. Being there is little voltage at the
center of the 1/2 wave elements, the boom is pretty much ignored by
the antenna. Also, it's at a 90 degree angle, which further reduces
coupling to the elements. My cushcraft tri-band beam uses an insulated
driven element, but most of the yagi's I build have all the elements
grounded to the boom. My three el 6m yagi has all the elements welded
to the boom, and the whole antenna, elements, boom, even the gamma
match tube, are all hard copper tubing. It's a one piece antenna. Or a
plumbers delight, as many call that method of construction... MK



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Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.682 / Virus Database: 444 - Release Date: 11/05/2004