Antenna problem

[captainvideo462002@yahoo.]

I need to mount a directional antenna vertically polarized on a mast.
The boom is about 9.0 feet long and the elements measure almost 6.0
feet across. The antenna was originally designed to be mounted from
the rear on a Rohn type of tower with two U bolts using two vertical
supports of the tower. This job site has no tower so we had planned to
chiminey mount this antenna on a single single 10.0 foot length of 1
11/16 OD galvanized rigid pipe. The problem is that the antenna, if
mounted this way would be so front heavy it would make this method
impractical.

In light of this, the manufacturer has reoriented the elements on the
boom so that we can now center mount this antenna and achieve a better
balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very close
to the driven element and the feed point and may effect the units'
impedance. The antenna has been pre tuned at the factory for the
operating frequency of 72.45MHZ and although the tuning slug can be
field adjusted it would not be technically appropriate to do this with
the antenna assembled on the ground, and it would be impossible to
accomplish with the antenna mounted on the roof. The final SWR reading
would tell the tale and at that point if the metal mast had detuned
the antenna, the whole thing would have to be taken down and tweaked
and be re installed, how many times is anyone's guess. This could be
quite laborious and something I would rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of non
metallic mast. Ideally its OD should be equal to the ID of the metal
mast. The non metallic pipe would mount to the antenna and the other
end would fit into the rigid metal pipe about a foot or so and be
secured with two .25 inch bolts drilled through the mast. As an
alternative, in the case of a non metallic pipe having a different OD
I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe for
this application. However I feel that this would be much too flexible,
and besides that I don't think that it would stand up to a cold New
Hampshire Winter very well either. A friend also offered that I might
use the PVC with a wooden dowel inside to stiffen it up, the whole
thing sealed up with silicone. That seems like it may be a bit
stronger however I'm still quite apprehensive about it as well. This
is a 350.00 antenna, (my cost), PVC is very brittle in the cold and I
definitely do not want to be eating the cost of a replacement antenna
and doing this job again after a snow or ice load takes it down, in
January.

The system transmitter puts out a 1.0 watt AM signal and the receiver
is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are successful.
This new antenna is replacing the poorly performing omnidirectional
one presently installed. The ERP of this directional antenna is
approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a referral
to a more appropriate News Group . Thanks very much, Lenny.

 

[GregS]

In article <e11de2ad-335e-4a4e-a5c9-938592ce0391@r24g2000yqd.googlegroups.com>, "captainvideo462002@yahoo.com" <captainvideo462002@yahoo.com> wrote:

I need to mount a directional antenna vertically polarized on a mast.
The boom is about 9.0 feet long and the elements measure almost 6.0
feet across. The antenna was originally designed to be mounted from
the rear on a Rohn type of tower with two U bolts using two vertical
supports of the tower. This job site has no tower so we had planned to
chiminey mount this antenna on a single single 10.0 foot length of 1
11/16 OD galvanized rigid pipe. The problem is that the antenna, if
mounted this way would be so front heavy it would make this method
impractical.

In light of this, the manufacturer has reoriented the elements on the
boom so that we can now center mount this antenna and achieve a better
balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very close
to the driven element and the feed point and may effect the units'
impedance. The antenna has been pre tuned at the factory for the
operating frequency of 72.45MHZ and although the tuning slug can be
field adjusted it would not be technically appropriate to do this with
the antenna assembled on the ground, and it would be impossible to
accomplish with the antenna mounted on the roof. The final SWR reading
would tell the tale and at that point if the metal mast had detuned
the antenna, the whole thing would have to be taken down and tweaked
and be re installed, how many times is anyone's guess. This could be
quite laborious and something I would rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of non
metallic mast. Ideally its OD should be equal to the ID of the metal
mast. The non metallic pipe would mount to the antenna and the other
end would fit into the rigid metal pipe about a foot or so and be
secured with two .25 inch bolts drilled through the mast. As an
alternative, in the case of a non metallic pipe having a different OD
I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe for
this application. However I feel that this would be much too flexible,
and besides that I don't think that it would stand up to a cold New
Hampshire Winter very well either. A friend also offered that I might
use the PVC with a wooden dowel inside to stiffen it up, the whole
thing sealed up with silicone. That seems like it may be a bit
stronger however I'm still quite apprehensive about it as well. This
is a 350.00 antenna, (my cost), PVC is very brittle in the cold and I
definitely do not want to be eating the cost of a replacement antenna
and doing this job again after a snow or ice load takes it down, in
January.

The system transmitter puts out a 1.0 watt AM signal and the receiver
is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are successful.
This new antenna is replacing the poorly performing omnidirectional
one presently installed. The ERP of this directional antenna is
approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a referral
to a more appropriate News Group . Thanks very much, Lenny.

I was trying to visualize the antenna. Why
not go 50/50 or some ratio to break up the mast, with
metal bottom, then turn to PVC getting slose to the element.
You can also go metal/PVC/metal, to clamp to the boom.


greg

 

On Thu, 5 Nov 2009 09:22:10 -0800 (PST),
"captainvideo462002@yahoo.com" <captainvideo462002@yahoo.com> wrote:

I need to mount a directional antenna vertically polarized on a mast.
The boom is about 9.0 feet long and the elements measure almost 6.0
feet across. The antenna was originally designed to be mounted from
the rear on a Rohn type of tower with two U bolts using two vertical
supports of the tower. This job site has no tower so we had planned to
chiminey mount this antenna on a single single 10.0 foot length of 1
11/16 OD galvanized rigid pipe. The problem is that the antenna, if
mounted this way would be so front heavy it would make this method
impractical.

In light of this, the manufacturer has reoriented the elements on the
boom so that we can now center mount this antenna and achieve a better
balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very close
to the driven element and the feed point and may effect the units'
impedance.

Approximately center the mount between elements and it will be fine.

The antenna has been pre tuned at the factory for the
operating frequency of 72.45MHZ and although the tuning slug can be
field adjusted it would not be technically appropriate to do this with
the antenna assembled on the ground, and it would be impossible to
accomplish with the antenna mounted on the roof. The final SWR reading
would tell the tale and at that point if the metal mast had detuned
the antenna, the whole thing would have to be taken down and tweaked
and be re installed, how many times is anyone's guess. This could be
quite laborious and something I would rather not get involved in.

With the antenna and mast at ground level.
Position the reflector close to the ground.
Have the antenna pointing straight up.
Set your initial match this way.
This may be all you have to do.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of non
metallic mast. Ideally its OD should be equal to the ID of the metal
mast. The non metallic pipe would mount to the antenna and the other
end would fit into the rigid metal pipe about a foot or so and be
secured with two .25 inch bolts drilled through the mast. As an
alternative, in the case of a non metallic pipe having a different OD
I would then U bolt it to the steel mast.

This suggestion shows how much the manufacturer does not know.
The RF can't tell the difference between a conducting mast or the
conducting outer shield of the coax that runs down a fiberglass mast.
Use the metal mast.

It has been suggested that I consider using schedule 80 PVC pipe for
this application. However I feel that this would be much too flexible,
and besides that I don't think that it would stand up to a cold New
Hampshire Winter very well either. A friend also offered that I might
use the PVC with a wooden dowel inside to stiffen it up, the whole
thing sealed up with silicone. That seems like it may be a bit
stronger however I'm still quite apprehensive about it as well. This
is a 350.00 antenna, (my cost), PVC is very brittle in the cold and I
definitely do not want to be eating the cost of a replacement antenna
and doing this job again after a snow or ice load takes it down, in
January.

The system transmitter puts out a 1.0 watt AM signal and the receiver
is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are successful.
This new antenna is replacing the poorly performing omnidirectional
one presently installed. The ERP of this directional antenna is
approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a referral
to a more appropriate News Group . Thanks very much, Lenny.

Two questions.

How many elements?

How is the coax routed away from the driven element. Down the center
of the boom at the mast or off the end of the boom at the reflector
end?

 

[Bennett Price]

Take a look at http://www.mgs4u.com/fiberglass-tube-rod.htm

captainvideo462002@yahoo.com wrote:

I need to mount a directional antenna vertically polarized on a mast.
The boom is about 9.0 feet long and the elements measure almost 6.0
feet across. The antenna was originally designed to be mounted from
the rear on a Rohn type of tower with two U bolts using two vertical
supports of the tower. This job site has no tower so we had planned to
chiminey mount this antenna on a single single 10.0 foot length of 1
11/16 OD galvanized rigid pipe. The problem is that the antenna, if
mounted this way would be so front heavy it would make this method
impractical.

In light of this, the manufacturer has reoriented the elements on the
boom so that we can now center mount this antenna and achieve a better
balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very close
to the driven element and the feed point and may effect the units'
impedance. The antenna has been pre tuned at the factory for the
operating frequency of 72.45MHZ and although the tuning slug can be
field adjusted it would not be technically appropriate to do this with
the antenna assembled on the ground, and it would be impossible to
accomplish with the antenna mounted on the roof. The final SWR reading
would tell the tale and at that point if the metal mast had detuned
the antenna, the whole thing would have to be taken down and tweaked
and be re installed, how many times is anyone's guess. This could be
quite laborious and something I would rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of non
metallic mast. Ideally its OD should be equal to the ID of the metal
mast. The non metallic pipe would mount to the antenna and the other
end would fit into the rigid metal pipe about a foot or so and be
secured with two .25 inch bolts drilled through the mast. As an
alternative, in the case of a non metallic pipe having a different OD
I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe for
this application. However I feel that this would be much too flexible,
and besides that I don't think that it would stand up to a cold New
Hampshire Winter very well either. A friend also offered that I might
use the PVC with a wooden dowel inside to stiffen it up, the whole
thing sealed up with silicone. That seems like it may be a bit
stronger however I'm still quite apprehensive about it as well. This
is a 350.00 antenna, (my cost), PVC is very brittle in the cold and I
definitely do not want to be eating the cost of a replacement antenna
and doing this job again after a snow or ice load takes it down, in
January.

The system transmitter puts out a 1.0 watt AM signal and the receiver
is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are successful.
This new antenna is replacing the poorly performing omnidirectional
one presently installed. The ERP of this directional antenna is
approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a referral
to a more appropriate News Group . Thanks very much, Lenny.

 

[GregS]

In article <hcv6ti$sm3$1@usenet01.srv.cis.pitt.edu>, zekfrivo@zekfrivolous.com (GregS) wrote:

In article <e11de2ad-335e-4a4e-a5c9-938592ce0391@r24g2000yqd.googlegroups.com>,
"captainvideo462002@yahoo.com" <captainvideo462002@yahoo.com> wrote:
I need to mount a directional antenna vertically polarized on a mast.
The boom is about 9.0 feet long and the elements measure almost 6.0
feet across. The antenna was originally designed to be mounted from
the rear on a Rohn type of tower with two U bolts using two vertical
supports of the tower. This job site has no tower so we had planned to
chiminey mount this antenna on a single single 10.0 foot length of 1
11/16 OD galvanized rigid pipe. The problem is that the antenna, if
mounted this way would be so front heavy it would make this method
impractical.

In light of this, the manufacturer has reoriented the elements on the
boom so that we can now center mount this antenna and achieve a better
balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very close
to the driven element and the feed point and may effect the units'
impedance. The antenna has been pre tuned at the factory for the
operating frequency of 72.45MHZ and although the tuning slug can be
field adjusted it would not be technically appropriate to do this with
the antenna assembled on the ground, and it would be impossible to
accomplish with the antenna mounted on the roof. The final SWR reading
would tell the tale and at that point if the metal mast had detuned
the antenna, the whole thing would have to be taken down and tweaked
and be re installed, how many times is anyone's guess. This could be
quite laborious and something I would rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of non
metallic mast. Ideally its OD should be equal to the ID of the metal
mast. The non metallic pipe would mount to the antenna and the other
end would fit into the rigid metal pipe about a foot or so and be
secured with two .25 inch bolts drilled through the mast. As an
alternative, in the case of a non metallic pipe having a different OD
I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe for
this application. However I feel that this would be much too flexible,
and besides that I don't think that it would stand up to a cold New
Hampshire Winter very well either. A friend also offered that I might
use the PVC with a wooden dowel inside to stiffen it up, the whole
thing sealed up with silicone. That seems like it may be a bit
stronger however I'm still quite apprehensive about it as well. This
is a 350.00 antenna, (my cost), PVC is very brittle in the cold and I
definitely do not want to be eating the cost of a replacement antenna
and doing this job again after a snow or ice load takes it down, in
January.

The system transmitter puts out a 1.0 watt AM signal and the receiver
is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are successful.
This new antenna is replacing the poorly performing omnidirectional
one presently installed. The ERP of this directional antenna is
approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a referral
to a more appropriate News Group . Thanks very much, Lenny.

I was trying to visualize the antenna. Why
not go 50/50 or some ratio to break up the mast, with
metal bottom, then turn to PVC getting slose to the element.
You can also go metal/PVC/metal, to clamp to the boom.

The PVC coupling sounds great to me. I looked up some ferrite cores
to put around the mast. Pricey.

Just stay away from the element as far as possible, and stay away from 3 foot or
6 foot lenths of masting.

greg

 

[captainvideo462002@yahoo.]

On Nov 5, 5:34 pm, Bennett Price <bjpr...@cal.berkeley.edu> wrote:

Take a look athttp://www.mgs4u.com/fiberglass-tube-rod.htm



captainvideo462...@yahoo.com wrote:
I need to mount a directional antenna vertically polarized on a mast.
The boom is about 9.0 feet long and the elements measure almost 6.0
feet across. The antenna was originally designed to be mounted from
the rear on a Rohn type of tower with two U bolts using two vertical
supports of the tower. This job site has no tower so we had planned to
chiminey mount this antenna on a single single 10.0 foot length of 1
11/16 OD galvanized rigid pipe. The problem is that the antenna, if
mounted this way would be so front heavy it would make this method
impractical.

In light of this, the manufacturer has reoriented the elements on the
boom so that we can now center mount this antenna and achieve a better
balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very close
to the driven element and the feed point and may effect the units'
impedance. The antenna has been pre tuned at the factory for the
operating frequency of 72.45MHZ and although the tuning slug can be
field adjusted it would not be technically appropriate to do this with
the antenna assembled on the ground, and it would be impossible to
accomplish with the antenna mounted on the roof. The final SWR reading
would tell the tale and at that point if the metal mast had detuned
the antenna, the whole thing would have to be taken down and tweaked
and be re installed, how many times is anyone's guess. This could be
quite laborious and something I would rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of non
metallic mast. Ideally its OD should be equal to the ID of the metal
mast. The non metallic pipe would mount to the antenna and the other
end would fit into the rigid metal pipe about a foot or so and be
secured with two .25 inch bolts drilled through the mast. As an
alternative, in the case of a non metallic pipe having a different OD
I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe for
this application. However I feel that this would be much too flexible,
and besides that I don't think that it would stand up to a cold New
Hampshire Winter very well either. A friend also offered that I might
use the PVC with a wooden dowel inside to stiffen it up, the whole
thing sealed up with silicone. That seems like it may be a bit
stronger however I'm still quite apprehensive about it as well. This
is a 350.00 antenna, (my cost), PVC is very brittle in the cold and I
definitely do not want to be eating the cost of a replacement antenna
and doing this job again after a snow or ice load takes it down, in
January.

The system transmitter puts out a 1.0 watt AM signal and the receiver
is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are successful.
This new antenna is replacing the poorly performing omnidirectional
one presently installed. The ERP of this directional antenna is
approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a referral
to a more appropriate News Group . Thanks very much, Lenny.- Hide quoted text -

- Show quoted text -

I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

 

O

I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

What value does a non conducting mast have when it has a conducting
outer shield of the coax running down it? The RF isn't smart enough to
tell the difference.

 

[GregS]

In article <cnh8f5l12i1nlaahcn2gcv97b3i6cbldn2@4ax.com>, tnom@mucks.net wrote:

O
I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

What value does a non conducting mast have when it has a conducting
outer shield of the coax running down it? The RF isn't smart enough to
tell the difference.

Thats right. and its copper. You can however buy ferrite cores cheap to go around the coax
to prevent that.


greg

 

[baron]

captainvideo462002@yahoo.com Inscribed thus:

On Nov 5, 5:34 pm, Bennett Price <bjpr...@cal.berkeley.edu> wrote:
Take a look athttp://www.mgs4u.com/fiberglass-tube-rod.htm



captainvideo462...@yahoo.com wrote:
I need to mount a directional antenna vertically polarized on a
mast. The boom is about 9.0 feet long and the elements measure
almost 6.0 feet across. The antenna was originally designed to be
mounted from the rear on a Rohn type of tower with two U bolts
using two vertical supports of the tower. This job site has no
tower so we had planned to chiminey mount this antenna on a single
single 10.0 foot length of 1 11/16 OD galvanized rigid pipe. The
problem is that the antenna, if mounted this way would be so front
heavy it would make this method impractical.

In light of this, the manufacturer has reoriented the elements on
the boom so that we can now center mount this antenna and achieve a
better balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very
close to the driven element and the feed point and may effect the
units' impedance. The antenna has been pre tuned at the factory for
the operating frequency of 72.45MHZ and although the tuning slug
can be field adjusted it would not be technically appropriate to do
this with the antenna assembled on the ground, and it would be
impossible to accomplish with the antenna mounted on the roof. The
final SWR reading would tell the tale and at that point if the
metal mast had detuned the antenna, the whole thing would have to
be taken down and tweaked and be re installed, how many times is
anyone's guess. This could be quite laborious and something I would
rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of
non metallic mast. Ideally its OD should be equal to the ID of the
metal mast. The non metallic pipe would mount to the antenna and
the other end would fit into the rigid metal pipe about a foot or
so and be secured with two .25 inch bolts drilled through the mast.
As an alternative, in the case of a non metallic pipe having a
different OD I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe
for this application. However I feel that this would be much too
flexible, and besides that I don't think that it would stand up to
a cold New Hampshire Winter very well either. A friend also offered
that I might use the PVC with a wooden dowel inside to stiffen it
up, the whole thing sealed up with silicone. That seems like it may
be a bit stronger however I'm still quite apprehensive about it as
well. This is a 350.00 antenna, (my cost), PVC is very brittle in
the cold and I definitely do not want to be eating the cost of a
replacement antenna and doing this job again after a snow or ice
load takes it down, in January.

The system transmitter puts out a 1.0 watt AM signal and the
receiver is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are
successful. This new antenna is replacing the poorly performing
omnidirectional one presently installed. The ERP of this
directional antenna is approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a
referral to a more appropriate News Group . Thanks very much,
Lenny.- Hide quoted text -

- Show quoted text -

I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

That thing ! 7Dbd, a bit optimistic, more like 5.0/5.5Dbd if you're
lucky.

A 4mtr amateur antenna would be cheaper and just as good.

--
Best Regards:
Baron.

 

[baron]

GregS Inscribed thus:

In article <hcv6ti$sm3$1@usenet01.srv.cis.pitt.edu>,
zekfrivo@zekfrivolous.com (GregS) wrote:
In article
e11de2ad-335e-4a4e-a5c9-938592ce0391@r24g2000yqd.googlegroups.com>,
"captainvideo462002@yahoo.com" <captainvideo462002@yahoo.com> wrote:
I need to mount a directional antenna vertically polarized on a mast.
The boom is about 9.0 feet long and the elements measure almost 6.0
feet across. The antenna was originally designed to be mounted from
the rear on a Rohn type of tower with two U bolts using two vertical
supports of the tower. This job site has no tower so we had planned
to chiminey mount this antenna on a single single 10.0 foot length of
1 11/16 OD galvanized rigid pipe. The problem is that the antenna, if
mounted this way would be so front heavy it would make this method
impractical.

In light of this, the manufacturer has reoriented the elements on the
boom so that we can now center mount this antenna and achieve a
better balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very
close to the driven element and the feed point and may effect the
units' impedance. The antenna has been pre tuned at the factory for
the operating frequency of 72.45MHZ and although the tuning slug can
be field adjusted it would not be technically appropriate to do this
with the antenna assembled on the ground, and it would be impossible
to accomplish with the antenna mounted on the roof. The final SWR
reading would tell the tale and at that point if the metal mast had
detuned the antenna, the whole thing would have to be taken down and
tweaked and be re installed, how many times is anyone's guess. This
could be quite laborious and something I would rather not get
involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of non
metallic mast. Ideally its OD should be equal to the ID of the metal
mast. The non metallic pipe would mount to the antenna and the other
end would fit into the rigid metal pipe about a foot or so and be
secured with two .25 inch bolts drilled through the mast. As an
alternative, in the case of a non metallic pipe having a different OD
I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe for
this application. However I feel that this would be much too
flexible, and besides that I don't think that it would stand up to a
cold New Hampshire Winter very well either. A friend also offered
that I might use the PVC with a wooden dowel inside to stiffen it up,
the whole thing sealed up with silicone. That seems like it may be a
bit stronger however I'm still quite apprehensive about it as well.
This is a 350.00 antenna, (my cost), PVC is very brittle in the cold
and I definitely do not want to be eating the cost of a replacement
antenna and doing this job again after a snow or ice load takes it
down, in January.

The system transmitter puts out a 1.0 watt AM signal and the receiver
is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are successful.
This new antenna is replacing the poorly performing omnidirectional
one presently installed. The ERP of this directional antenna is
approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a referral
to a more appropriate News Group . Thanks very much, Lenny.

I was trying to visualize the antenna. Why
not go 50/50 or some ratio to break up the mast, with
metal bottom, then turn to PVC getting slose to the element.
You can also go metal/PVC/metal, to clamp to the boom.



The PVC coupling sounds great to me. I looked up some ferrite cores
to put around the mast. Pricey.

Just stay away from the element as far as possible, and stay away from
3 foot or 6 foot lenths of masting.

greg

If that is going to be mounted at the top of a pole then keep the top
part of the driven element above the mast. and run the co-ax down
inside the mast. I agree with avoiding any mast length that could be
resonant in the 70Mhz band.

--
Best Regards:
Baron.

 

On Fri, 06 Nov 2009 16:17:07 +0000, baron
<baron.nospam@linuxmaniac.nospam.net> wrote:

captainvideo462002@yahoo.com Inscribed thus:

On Nov 5, 5:34 pm, Bennett Price <bjpr...@cal.berkeley.edu> wrote:
Take a look athttp://www.mgs4u.com/fiberglass-tube-rod.htm



captainvideo462...@yahoo.com wrote:
I need to mount a directional antenna vertically polarized on a
mast. The boom is about 9.0 feet long and the elements measure
almost 6.0 feet across. The antenna was originally designed to be
mounted from the rear on a Rohn type of tower with two U bolts
using two vertical supports of the tower. This job site has no
tower so we had planned to chiminey mount this antenna on a single
single 10.0 foot length of 1 11/16 OD galvanized rigid pipe. The
problem is that the antenna, if mounted this way would be so front
heavy it would make this method impractical.

In light of this, the manufacturer has reoriented the elements on
the boom so that we can now center mount this antenna and achieve a
better balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very
close to the driven element and the feed point and may effect the
units' impedance. The antenna has been pre tuned at the factory for
the operating frequency of 72.45MHZ and although the tuning slug
can be field adjusted it would not be technically appropriate to do
this with the antenna assembled on the ground, and it would be
impossible to accomplish with the antenna mounted on the roof. The
final SWR reading would tell the tale and at that point if the
metal mast had detuned the antenna, the whole thing would have to
be taken down and tweaked and be re installed, how many times is
anyone's guess. This could be quite laborious and something I would
rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of
non metallic mast. Ideally its OD should be equal to the ID of the
metal mast. The non metallic pipe would mount to the antenna and
the other end would fit into the rigid metal pipe about a foot or
so and be secured with two .25 inch bolts drilled through the mast.
As an alternative, in the case of a non metallic pipe having a
different OD I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe
for this application. However I feel that this would be much too
flexible, and besides that I don't think that it would stand up to
a cold New Hampshire Winter very well either. A friend also offered
that I might use the PVC with a wooden dowel inside to stiffen it
up, the whole thing sealed up with silicone. That seems like it may
be a bit stronger however I'm still quite apprehensive about it as
well. This is a 350.00 antenna, (my cost), PVC is very brittle in
the cold and I definitely do not want to be eating the cost of a
replacement antenna and doing this job again after a snow or ice
load takes it down, in January.

The system transmitter puts out a 1.0 watt AM signal and the
receiver is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are
successful. This new antenna is replacing the poorly performing
omnidirectional one presently installed. The ERP of this
directional antenna is approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a
referral to a more appropriate News Group . Thanks very much,
Lenny.- Hide quoted text -

- Show quoted text -

I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

That thing ! 7Dbd, a bit optimistic, more like 5.0/5.5Dbd if you're
lucky.

A 4mtr amateur antenna would be cheaper and just as good.

To the OP:
You could also mount the thing on one side as designed and add a
counterweight on the opposite side to balance it.

 

[GregS]

In article <dmk8f5tqqk02r5nkppvdeb1389djdn5evc@4ax.com>, greenpjs@neo.rr.com wrote:

On Fri, 06 Nov 2009 16:17:07 +0000, baron
baron.nospam@linuxmaniac.nospam.net> wrote:

captainvideo462002@yahoo.com Inscribed thus:

On Nov 5, 5:34 pm, Bennett Price <bjpr...@cal.berkeley.edu> wrote:
Take a look athttp://www.mgs4u.com/fiberglass-tube-rod.htm



captainvideo462...@yahoo.com wrote:
I need to mount a directional antenna vertically polarized on a
mast. The boom is about 9.0 feet long and the elements measure
almost 6.0 feet across. The antenna was originally designed to be
mounted from the rear on a Rohn type of tower with two U bolts
using two vertical supports of the tower. This job site has no
tower so we had planned to chiminey mount this antenna on a single
single 10.0 foot length of 1 11/16 OD galvanized rigid pipe. The
problem is that the antenna, if mounted this way would be so front
heavy it would make this method impractical.

In light of this, the manufacturer has reoriented the elements on
the boom so that we can now center mount this antenna and achieve a
better balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very
close to the driven element and the feed point and may effect the
units' impedance. The antenna has been pre tuned at the factory for
the operating frequency of 72.45MHZ and although the tuning slug
can be field adjusted it would not be technically appropriate to do
this with the antenna assembled on the ground, and it would be
impossible to accomplish with the antenna mounted on the roof. The
final SWR reading would tell the tale and at that point if the
metal mast had detuned the antenna, the whole thing would have to
be taken down and tweaked and be re installed, how many times is
anyone's guess. This could be quite laborious and something I would
rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of
non metallic mast. Ideally its OD should be equal to the ID of the
metal mast. The non metallic pipe would mount to the antenna and
the other end would fit into the rigid metal pipe about a foot or
so and be secured with two .25 inch bolts drilled through the mast.
As an alternative, in the case of a non metallic pipe having a
different OD I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe
for this application. However I feel that this would be much too
flexible, and besides that I don't think that it would stand up to
a cold New Hampshire Winter very well either. A friend also offered
that I might use the PVC with a wooden dowel inside to stiffen it
up, the whole thing sealed up with silicone. That seems like it may
be a bit stronger however I'm still quite apprehensive about it as
well. This is a 350.00 antenna, (my cost), PVC is very brittle in
the cold and I definitely do not want to be eating the cost of a
replacement antenna and doing this job again after a snow or ice
load takes it down, in January.

The system transmitter puts out a 1.0 watt AM signal and the
receiver is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are
successful. This new antenna is replacing the poorly performing
omnidirectional one presently installed. The ERP of this
directional antenna is approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a
referral to a more appropriate News Group . Thanks very much,
Lenny.- Hide quoted text -

- Show quoted text -

I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

That thing ! 7Dbd, a bit optimistic, more like 5.0/5.5Dbd if you're
lucky.

A 4mtr amateur antenna would be cheaper and just as good.

To the OP:
You could also mount the thing on one side as designed and add a
counterweight on the opposite side to balance it.

You could also compromise. Mount it offset and add counterweight if necessary.

greg

 

[hr(bob) hofmann@att.net]

On Nov 6, 11:29 am, zekfr...@zekfrivolous.com (GregS) wrote:

In article <dmk8f5tqqk02r5nkppvdeb1389djdn5...@4ax.com>, green...@neo.rr.com wrote:
On Fri, 06 Nov 2009 16:17:07 +0000, baron
baron.nos...@linuxmaniac.nospam.net> wrote:

captainvideo462...@yahoo.com Inscribed thus:

On Nov 5, 5:34 pm, Bennett Price <bjpr...@cal.berkeley.edu> wrote:
Take a look athttp://www.mgs4u.com/fiberglass-tube-rod.htm

captainvideo462...@yahoo.com wrote:
I need to mount a directional antenna vertically polarized on a
mast. The boom is about 9.0 feet long and the elements measure
almost 6.0 feet across. The antenna was originally designed to be
mounted from the rear on a Rohn type of tower with two U bolts
using two vertical supports of the tower. This job site has no
tower so we had planned to chiminey mount this antenna on a single
single 10.0 foot length of 1 11/16 OD galvanized rigid pipe. The
problem is that the antenna, if mounted this way would be so front
heavy it would make this method impractical.

In light of this, the manufacturer has reoriented the elements on
the boom so that we can now center mount this antenna and achieve a
better balance, however there is now a special consideration.

In this arrangement the metal mast, (pipe) will now come up very
close to the driven element and the feed point and may effect the
units' impedance. The antenna has been pre tuned at the factory for
the operating frequency of 72.45MHZ and although the tuning slug
can be field adjusted it would not be technically appropriate to do
this with the antenna assembled on the ground, and it would be
impossible to accomplish with the antenna mounted on the roof. The
final SWR reading would tell the tale and at that point if the
metal mast had detuned the antenna, the whole thing would have to
be taken down and tweaked and be re installed, how many times is
anyone's guess. This could be quite laborious and something I would
rather not get involved in.

To address this possibility of detuning, the manufacturer has
suggested that I obtain about a 5 or 6 foot piece of some sort of
non metallic mast. Ideally its OD should be equal to the ID of the
metal mast. The non metallic pipe would mount to the antenna and
the other end would fit into the rigid metal pipe about a foot or
so and be secured with two .25 inch bolts drilled through the mast..
As an alternative, in the case of a non metallic pipe having a
different OD I would then U bolt it to the steel mast.

It has been suggested that I consider using schedule 80 PVC pipe
for this application. However I feel that this would be much too
flexible, and besides that I don't think that it would stand up to
a cold New Hampshire Winter very well either. A friend also offered
that I might use the PVC with a wooden dowel inside to stiffen it
up, the whole thing sealed up with silicone. That seems like it may
be a bit stronger however I'm still quite apprehensive about it as
well. This is a 350.00 antenna, (my cost), PVC is very brittle in
the cold and I definitely do not want to be eating the cost of a
replacement antenna and doing this job again after a snow or ice
load takes it down, in January.

The system transmitter puts out a 1.0 watt AM signal and the
receiver is located almost ten miles away. The terrain is hilly and
mountainous. There are other installations close by which use
directional antennas aimed at this receiver site that are
successful. This new antenna is replacing the poorly performing
omnidirectional one presently installed. The ERP of this
directional antenna is approximately 6.0 watts.

Has anyone ever dealt with anything like this? I would really
appreciate any advice, on mounting arrangements or perhaps a
referral to a more appropriate News Group . Thanks very much,
Lenny.- Hide quoted text -

- Show quoted text -

I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

That thing !  7Dbd, a bit optimistic, more like 5.0/5.5Dbd if you're
lucky.

A 4mtr amateur antenna would be cheaper and just as good.

To the OP:
You could also mount the thing on one side as designed and add a
counterweight on the opposite side to balance it.  

You could also compromise. Mount it offset and add counterweight if necessary.

greg- Hide quoted text -

- Show quoted text -

What frequency are you using?

 

On Fri, 06 Nov 2009 16:06:11 GMT, zekfrivo@zekfrivolous.com (GregS)
wrote:

In article <cnh8f5l12i1nlaahcn2gcv97b3i6cbldn2@4ax.com>, tnom@mucks.net wrote:
O
I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

What value does a non conducting mast have when it has a conducting
outer shield of the coax running down it? The RF isn't smart enough to
tell the difference.

Thats right. and its copper. You can however buy ferrite cores cheap to go around the coax
to prevent that.


greg

Having the driven element inline or close to a conducting mast is
done all the time. It has negligible effect on the performance
of the antenna.

If the OP insists on a non conducting mast because he is concerned
with de tuning then he should also be concerned with the coax routed
at that same mast location also de tuning the antenna.

The only solution if the OP insists on a non conductive mast is to
route the coax behind the reflector and drop it down from there.
Have the length of the coax between the boom and the mast
about 12 feet long( half wavelength). This length will create a
high impedance path that will be grounded and will have no ill
effect.

l l l l
l_ l_ _ l_ l_
l l l l l l
l l l l l l
l /
l /
l /
l /
ll -----ground here
ll

 

[captainvideo462002@yahoo.]

On Nov 6, 4:58 pm, t...@mucks.net wrote:

On Fri, 06 Nov 2009 16:06:11 GMT, zekfr...@zekfrivolous.com (GregS)
wrote:





In article <cnh8f5l12i1nlaahcn2gcv97b3i6cbl...@4ax.com>, t...@mucks.net wrote:
O
I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=CCS-PLHC-374&p=162260&sc=0

What value does a non conducting mast have when it has a conducting
outer shield of the coax running down it? The RF isn't smart enough to
tell the difference.

Thats right. and its copper. You can however buy ferrite cores cheap to go around the coax
to prevent that.

greg

Having the driven element inline or close to a conducting mast is
done all the time. It has negligible effect on the performance
of the antenna.

If the OP insists on a non conducting mast because he is concerned
with de tuning then he should also be concerned with the coax routed
at that same mast location also de tuning the antenna.

The only solution if the OP insists on a non conductive mast is to
route the coax behind the reflector and drop it down from there.
Have the length of the coax between the boom and the mast
about 12 feet long( half wavelength). This length will create a
high impedance path that will be grounded and will have no ill
effect.

l   l       l   l
l_ l_ _  l_ l_
l   l   l   l   l  l
l   l   l   l   l  l
       l        /
       l      /
       l    /
       l /
       ll  -----ground here
       ll- Hide quoted text -

- Show quoted text -

I like the idea of off setting the antenna on a horizontal at the top
of the mast. However the operating freq. is 72MHZ and so this thing is
somewhat heavy. How far out from the vertical should the antenna sit?
There will be a great deal of torque from the offset so this is a
concern. Counterbalancing is a thought but hopefully will not be
necessary unless this has to stick out quite a bit. Lenny

 

[GregS]

In article <9753c186-4d23-4656-99a1-318854f88836@j24g2000yqa.googlegroups.com>, "captainvideo462002@yahoo.com" <captainvideo462002@yahoo.com> wrote:

On Nov 6, 4:58=A0pm, t...@mucks.net wrote:
On Fri, 06 Nov 2009 16:06:11 GMT, zekfr...@zekfrivolous.com (GregS)
wrote:





In article <cnh8f5l12i1nlaahcn2gcv97b3i6cbl...@4ax.com>, t...@mucks.net =
wrote:
O
I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=3DCCS-PLHC-374&p=3D162260&=
sc=3D0

What value does a non conducting mast have when it has a conducting
outer shield of the coax running down it? The RF isn't smart enough to
tell the difference.

Thats right. and its copper. You can however buy ferrite cores cheap to =
go around the coax
to prevent that.

greg

Having the driven element inline or close to a conducting mast is
done all the time. It has negligible effect on the performance
of the antenna.

If the OP insists on a non conducting mast because he is concerned
with de tuning then he should also be concerned with the coax routed
at that same mast location also de tuning the antenna.

The only solution if the OP insists on a non conductive mast is to
route the coax behind the reflector and drop it down from there.
Have the length of the coax between the boom and the mast
about 12 feet long( half wavelength). This length will create a
high impedance path that will be grounded and will have no ill
effect.

l =A0 l =A0 =A0 =A0 l =A0 l
l_ l_ _ =A0l_ l_
l =A0 l =A0 l =A0 l =A0 l =A0l
l =A0 l =A0 l =A0 l =A0 l =A0l
=A0 =A0 =A0 =A0l =A0 =A0 =A0 =A0/
=A0 =A0 =A0 =A0l =A0 =A0 =A0/
=A0 =A0 =A0 =A0l =A0 =A0/
=A0 =A0 =A0 =A0l /
=A0 =A0 =A0 =A0ll =A0-----ground here
=A0 =A0 =A0 =A0ll- Hide quoted text -

- Show quoted text -

I like the idea of off setting the antenna on a horizontal at the top
of the mast. However the operating freq. is 72MHZ and so this thing is
somewhat heavy. How far out from the vertical should the antenna sit?
There will be a great deal of torque from the offset so this is a
concern. Counterbalancing is a thought but hopefully will not be
necessary unless this has to stick out quite a bit. Lenny

Looking at the antenna again, I would put it half way between the driven and reflector.
You have an extra stub on the end to add a little weight. Don't need too much.
It doesn't have to be perfect.

greg

 

[captainvideo462002@yahoo.]

On Nov 11, 3:53 pm, zekfr...@zekfrivolous.com (GregS) wrote:

In article <9753c186-4d23-4656-99a1-318854f88...@j24g2000yqa.googlegroups..com>, "captainvideo462...@yahoo.com" <captainvideo462...@yahoo.com> wrote:



On Nov 6, 4:58=A0pm, t...@mucks.net wrote:
On Fri, 06 Nov 2009 16:06:11 GMT, zekfr...@zekfrivolous.com (GregS)
wrote:

In article <cnh8f5l12i1nlaahcn2gcv97b3i6cbl...@4ax.com>, t...@mucks.net > >wrote:
O
I meant to add the link for the antenna. Also I was told to route the
coax around the rear of the boom and sort of wrap it around the back
keeping it tight to the boomand then come down the mast with it. If
this makes any sense.

http://www.hol4g.com/ac/product.aspx?number=3DCCS-PLHC-374&p=3D162260&> >sc=3D0

What value does a non conducting mast have when it has a conducting
outer shield of the coax running down it? The RF isn't smart enough to
tell the difference.

Thats right. and its copper. You can however buy ferrite cores cheap to > >go around the coax
to prevent that.

greg

Having the driven element inline or close to a conducting mast is
done all the time. It has negligible effect on the performance
of the antenna.

If the OP insists on a non conducting mast because he is concerned
with de tuning then he should also be concerned with the coax routed
at that same mast location also de tuning the antenna.

The only solution if the OP insists on a non conductive mast is to
route the coax behind the reflector and drop it down from there.
Have the length of the coax between the boom and the mast
about 12 feet long( half wavelength). This length will create a
high impedance path that will be grounded and will have no ill
effect.

l =A0 l =A0 =A0 =A0 l =A0 l
l_ l_ _ =A0l_ l_
l =A0 l =A0 l =A0 l =A0 l =A0l
l =A0 l =A0 l =A0 l =A0 l =A0l
=A0 =A0 =A0 =A0l =A0 =A0 =A0 =A0/
=A0 =A0 =A0 =A0l =A0 =A0 =A0/
=A0 =A0 =A0 =A0l =A0 =A0/
=A0 =A0 =A0 =A0l /
=A0 =A0 =A0 =A0ll =A0-----ground here
=A0 =A0 =A0 =A0ll- Hide quoted text -

- Show quoted text -

I like the idea of off setting the antenna on a horizontal at the top
of the mast. However the operating freq. is 72MHZ and so this thing is
somewhat heavy. How far out from the vertical should the antenna sit?
There will be a great deal of torque from the offset so this is a
concern. Counterbalancing is a thought but hopefully will not be
necessary unless this has to stick out quite a bit. Lenny

Looking at the antenna again, I would put it half way between the driven and reflector.
You have an extra stub on the end to add a little weight. Don't need too much.
It doesn't have to be perfect.

greg

So would that make the inverted "L" or "T" portion of the antenna at
the top about 6 inches? Then as I picture this the antenna would be
out away from the mast by only that amount? I'm just having a hard
time picturing this. Lenny


counter weight----- ____
goes here l ------antenna mounts
vertically polarized out here
l
l
10 foot mast--------- l
l
l
l
l