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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 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.
"captainvideo462...@yahoo.com" <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.
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?
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.
> 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.
In article <hcv6ti$sm...@usenet01.srv.cis.pitt.edu>, zekfr...@zekfrivolous.com (GregS) wrote: >In article <e11de2ad-335e-4a4e-a5c9-938592ce0...@r24g2000yqd.googlegroups.com>, > "captainvideo462...@yahoo.com" <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.
>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.
>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.
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.
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.
>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.
>> 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.
> In article <hcv6ti$sm...@usenet01.srv.cis.pitt.edu>, > zekfr...@zekfrivolous.com (GregS) wrote: >>In article >><e11de2ad-335e-4a4e-a5c9-938592ce0...@r24g2000yqd.googlegroups.com>, >> "captainvideo462...@yahoo.com" <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.
>>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.
>>> 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.
>>>> 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.
> >>>> 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.
>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.
>>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
> 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.
> >>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
>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.
>> >>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.
> 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.
> >> >>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
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