I was wondering if you have to bring down an FM directional antenna to make changes to its pattern, then restore or replace it...or if it can be done with the elements in place? AM's frequently make noticeable changes in their DA patterns with the towers they started with...it's expensive to do otherwise and of course there are NIMBY issues. What brought this question up is a pending change to WBUR-FM ch. 215 90.9 Boston. They have (or had) an auxiliary tower and NDA antenna close in to Boston that was its main facility for several years. Its current DA is near the top of a former TV stick in the suburbs, about 1000-feet high. I surmised that while doing the switchover, they'd perhaps use the old NDA antenna, but the signal has remained unchanged for a while. The Frozen Candy Concoction applications page says WBUR is this close (!!) to the new operation.
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Adjusting FM Da's
- Thread starter Shellanswerman
- Start date
K
kilowatt
Guest
You don't see someone take down an FM DA.
The DA is an antenna and multiple elements (parasitics)which are set at the factory.
Conceivable that the antenna would be re-used and parasitics might be changed. Most of the time the Commission wants to see the real antenna tuned on a test range and shipped to your town.
> I was wondering if you have to bring down an FM directional
> antenna to make changes to its pattern, then restore or
> replace it...or if it can be done with the elements in
> place? AM's frequently make noticeable changes in their DA
> patterns with the towers they started with...it's expensive
> to do otherwise and of course there are NIMBY issues. What
> brought this question up is a pending change to WBUR-FM ch.
> 215 90.9 Boston. They have (or had) an auxiliary tower and
> NDA antenna close in to Boston that was its main facility
> for several years. Its current DA is near the top of a
> former TV stick in the suburbs, about 1000-feet high. I
> surmised that while doing the switchover, they'd perhaps use
> the old NDA antenna, but the signal has remained unchanged
> for a while. The Frozen Candy Concoction applications page
> says WBUR is this close (!!) to the new operation.
>
The DA is an antenna and multiple elements (parasitics)which are set at the factory.
Conceivable that the antenna would be re-used and parasitics might be changed. Most of the time the Commission wants to see the real antenna tuned on a test range and shipped to your town.
> I was wondering if you have to bring down an FM directional
> antenna to make changes to its pattern, then restore or
> replace it...or if it can be done with the elements in
> place? AM's frequently make noticeable changes in their DA
> patterns with the towers they started with...it's expensive
> to do otherwise and of course there are NIMBY issues. What
> brought this question up is a pending change to WBUR-FM ch.
> 215 90.9 Boston. They have (or had) an auxiliary tower and
> NDA antenna close in to Boston that was its main facility
> for several years. Its current DA is near the top of a
> former TV stick in the suburbs, about 1000-feet high. I
> surmised that while doing the switchover, they'd perhaps use
> the old NDA antenna, but the signal has remained unchanged
> for a while. The Frozen Candy Concoction applications page
> says WBUR is this close (!!) to the new operation.
>
T
TXengineer
Guest
And WBUR will purchase a new antenna.
The old one is at least a 20 years old Shively.
>
The old one is at least a 20 years old Shively.
>
WHY a new antenna?
I hope ya don't mind a question from a person just learnin' this stuff.
WHY are antennas replaced? Obviously, if changes make it necessary. But I have seen situations where a new antenna is installed with no real changes to the signal.
Has technology changed that much? Is there new antenna information that did not exist 20 years ago?
WHat wears out an antenna? My guesses are: Exposure to the elements, corrosion of the metal - that sort of thing.
Is there something inherent when ya pump a bunch of RF through something that degenerates that something over time?
Any info greatly appreciated.
> And WBUR will purchase a new antenna.
> The old one is at least a 20 years old Shively.
>
> >
>
I hope ya don't mind a question from a person just learnin' this stuff.
WHY are antennas replaced? Obviously, if changes make it necessary. But I have seen situations where a new antenna is installed with no real changes to the signal.
Has technology changed that much? Is there new antenna information that did not exist 20 years ago?
WHat wears out an antenna? My guesses are: Exposure to the elements, corrosion of the metal - that sort of thing.
Is there something inherent when ya pump a bunch of RF through something that degenerates that something over time?
Any info greatly appreciated.
> And WBUR will purchase a new antenna.
> The old one is at least a 20 years old Shively.
>
> >
>
Re: WHY a new antenna?
> WHY are antennas replaced? Obviously, if changes make it
> necessary. But I have seen situations where a new antenna
> is installed with no real changes to the signal.
> Has technology changed that much? Is there new antenna
> information that did not exist 20 years ago?
Yes, the field of antenna design has changed a bit, and there have been refinements to many models.
> WHat wears out an antenna? My guesses are: Exposure to the
> elements, corrosion of the metal - that sort of thing.
>
> Is there something inherent when ya pump a bunch of RF
> through something that degenerates that something over time?
OK, I'll give you an example. Try hanging from a tower, 24 hours a day, 365 days a year, rain, ice, sun, freeze and all. Marine brass and stainless steel just sort of wears down from weather. And then there are the issues of heating/cooling/expansion/contraction of the internal bullets (connectors), and all the other things that come with extreme exposure to the elements.
And if the antenna has electrical de-icers, they wear out or burn out in too short of a time as well.
> WHY are antennas replaced? Obviously, if changes make it
> necessary. But I have seen situations where a new antenna
> is installed with no real changes to the signal.
> Has technology changed that much? Is there new antenna
> information that did not exist 20 years ago?
Yes, the field of antenna design has changed a bit, and there have been refinements to many models.
> WHat wears out an antenna? My guesses are: Exposure to the
> elements, corrosion of the metal - that sort of thing.
>
> Is there something inherent when ya pump a bunch of RF
> through something that degenerates that something over time?
OK, I'll give you an example. Try hanging from a tower, 24 hours a day, 365 days a year, rain, ice, sun, freeze and all. Marine brass and stainless steel just sort of wears down from weather. And then there are the issues of heating/cooling/expansion/contraction of the internal bullets (connectors), and all the other things that come with extreme exposure to the elements.
And if the antenna has electrical de-icers, they wear out or burn out in too short of a time as well.
Re: WHY a new antenna?
If the line and antenna are pressurized, then there are rubber (well, more likely neoprene) gaskets which can get hard and leaky after a while. As well as hardware that can corrode, especially if the antenna is only a few miles downwind of a coal fired power plant!! As ours was.
Our 4 bay ERI antenna was hauled up to the top of our 200 foot tower back in 1988. Last year, we needed to install two four foot dishes on-top of our tower for a new station. We didn't think it was wise to add any more sections to our old Rohn 45 G tower. So we built a new 220' solid rod 18" face tower just beside the old tower. Since we had to move the antenna anyway, we felt it made more sense to bring the antenna down, clean it up, replace gaskets and re-install. Had complete hardware kit and gaskets on-hand from ERI when the tower crew got that far, only off air for about 5 hours.
Considering labor costs etc. for an antenna on a 1,000 foot tower, it makes more sense to just replace the antenna with a new one. Especially a directional.
If the line and antenna are pressurized, then there are rubber (well, more likely neoprene) gaskets which can get hard and leaky after a while. As well as hardware that can corrode, especially if the antenna is only a few miles downwind of a coal fired power plant!! As ours was.
Our 4 bay ERI antenna was hauled up to the top of our 200 foot tower back in 1988. Last year, we needed to install two four foot dishes on-top of our tower for a new station. We didn't think it was wise to add any more sections to our old Rohn 45 G tower. So we built a new 220' solid rod 18" face tower just beside the old tower. Since we had to move the antenna anyway, we felt it made more sense to bring the antenna down, clean it up, replace gaskets and re-install. Had complete hardware kit and gaskets on-hand from ERI when the tower crew got that far, only off air for about 5 hours.
Considering labor costs etc. for an antenna on a 1,000 foot tower, it makes more sense to just replace the antenna with a new one. Especially a directional.
Re: WHY a new antenna?
> WHY are antennas replaced? Obviously, if changes make it
> necessary. But I have seen situations where a new antenna
> is installed with no real changes to the signal.
>
> Has technology changed that much? Is there new antenna
> information that did not exist 20 years ago?
>
In addition to the improvements in modern antennas, and the deterioration of some parts, there is another reason to sometimes replace a 15 or 20 year old antenna.
The station may have been under different management back then. They may have been operation a killer cash-cow A.M. station and they at that time looked upon the FM station as an investment in the future that might or might not remain part of the family. So they put up a cheap antenna without paying for the right research. TODAY'S manager may get all the proper advice and put up the antenna that should have gone up there 20 years ago.
> WHY are antennas replaced? Obviously, if changes make it
> necessary. But I have seen situations where a new antenna
> is installed with no real changes to the signal.
>
> Has technology changed that much? Is there new antenna
> information that did not exist 20 years ago?
>
In addition to the improvements in modern antennas, and the deterioration of some parts, there is another reason to sometimes replace a 15 or 20 year old antenna.
The station may have been under different management back then. They may have been operation a killer cash-cow A.M. station and they at that time looked upon the FM station as an investment in the future that might or might not remain part of the family. So they put up a cheap antenna without paying for the right research. TODAY'S manager may get all the proper advice and put up the antenna that should have gone up there 20 years ago.
T
TXengineer
Guest
Re: WHY a new antenna?
> WHY are antennas replaced?
All the below reasons are good examples of why.
However WBUR is changing the pattern on theirs, so a new
antenna will be necessary.
> WHY are antennas replaced?
All the below reasons are good examples of why.
However WBUR is changing the pattern on theirs, so a new
antenna will be necessary.
T
THEInsultant
Guest
Re: WHY a new antenna?
> If the line and antenna are pressurized, then there are
> rubber (well, more likely neoprene) gaskets which can get
> hard and leaky after a while. As well as hardware that can
> corrode, especially if the antenna is only a few miles
> downwind of a coal fired power plant!! As ours was.
>
> Our 4 bay ERI antenna was hauled up to the top of our 200
> foot tower back in 1988. Last year, we needed to install two
> four foot dishes on-top of our tower for a new station. We
> didn't think it was wise to add any more sections to our old
> Rohn 45 G tower. So we built a new 220' solid rod 18" face
> tower just beside the old tower. Since we had to move the
> antenna anyway, we felt it made more sense to bring the
> antenna down, clean it up, replace gaskets and re-install.
> Had complete hardware kit and gaskets on-hand from ERI when
> the tower crew got that far, only off air for about 5 hours.
>
>
> Considering labor costs etc. for an antenna on a 1,000 foot
> tower, it makes more sense to just replace the antenna with
> a new one. Especially a directional.
>
Besides, Shively antennas suck IMHO. I'm glad to hear you guys are getting something better.
<P ID="signature">______________
--- THE Insultant ---</P>
> If the line and antenna are pressurized, then there are
> rubber (well, more likely neoprene) gaskets which can get
> hard and leaky after a while. As well as hardware that can
> corrode, especially if the antenna is only a few miles
> downwind of a coal fired power plant!! As ours was.
>
> Our 4 bay ERI antenna was hauled up to the top of our 200
> foot tower back in 1988. Last year, we needed to install two
> four foot dishes on-top of our tower for a new station. We
> didn't think it was wise to add any more sections to our old
> Rohn 45 G tower. So we built a new 220' solid rod 18" face
> tower just beside the old tower. Since we had to move the
> antenna anyway, we felt it made more sense to bring the
> antenna down, clean it up, replace gaskets and re-install.
> Had complete hardware kit and gaskets on-hand from ERI when
> the tower crew got that far, only off air for about 5 hours.
>
>
> Considering labor costs etc. for an antenna on a 1,000 foot
> tower, it makes more sense to just replace the antenna with
> a new one. Especially a directional.
>
Besides, Shively antennas suck IMHO. I'm glad to hear you guys are getting something better.
<P ID="signature">______________
--- THE Insultant ---</P>
T
TXengineer
Guest
Re: WHY a new antenna?
> Besides, Shively antennas suck IMHO. I'm glad to hear you
> guys are getting something better.
You seem to be confused.
TPT is talking about a station he has with an ERI 4 bay on it.
WBUR, the other poster, has a 2 bay Shively which will probably be replaced with another Shively.
Personally, I like the Shively antennas, I think they out perform ERI's when it comes to the meat... the signal. Although I think the ERI's out perform the Shivelys when it comes to ruggedness.
Still, personally, my favorite of all the brands is Dielectric. I think they have the best antenna going...
> Besides, Shively antennas suck IMHO. I'm glad to hear you
> guys are getting something better.
You seem to be confused.
TPT is talking about a station he has with an ERI 4 bay on it.
WBUR, the other poster, has a 2 bay Shively which will probably be replaced with another Shively.
Personally, I like the Shively antennas, I think they out perform ERI's when it comes to the meat... the signal. Although I think the ERI's out perform the Shivelys when it comes to ruggedness.
Still, personally, my favorite of all the brands is Dielectric. I think they have the best antenna going...
Re: WHY a new antenna?
The big panel Shiveleys seem to be good antennas.
The little ones I wouldn't trust any higher up than I can climb
That's about 20 feet.
The omni antennas tend to be unintentionally directional, which is why some folks with suburban sites may favor them. (If they can get the lobe shooting into town). But they are dinky little things I wouldn't trust to last past the first ice storm.
I have 2 ERI's on the air & my first 3 bay (1983) is still on the air somewhere. (Came dowm to be replaced by a 4 bay, into a new station in Defiance, replaced there with a 2 bay, into a new station in Indiana, then off somewhere else).
But the original question was why replace the antenna, in the case cited--up a tall tower, the cost of a new antenna is such a small cost of the entire project that it's prudent to just plan on replacing the antenna rather than risk extensive down time in order to salvage the old antenna.
The big panel Shiveleys seem to be good antennas.
The little ones I wouldn't trust any higher up than I can climb
That's about 20 feet.
The omni antennas tend to be unintentionally directional, which is why some folks with suburban sites may favor them. (If they can get the lobe shooting into town). But they are dinky little things I wouldn't trust to last past the first ice storm.
I have 2 ERI's on the air & my first 3 bay (1983) is still on the air somewhere. (Came dowm to be replaced by a 4 bay, into a new station in Defiance, replaced there with a 2 bay, into a new station in Indiana, then off somewhere else).
But the original question was why replace the antenna, in the case cited--up a tall tower, the cost of a new antenna is such a small cost of the entire project that it's prudent to just plan on replacing the antenna rather than risk extensive down time in order to salvage the old antenna.
K
kilowatt
Guest
Re: WHY a new antenna?
Everyone has a least one antenna horror story.
I have a dielectric in abox somewhere (panel) that couldn't be installed because the installers felt the thing was ready to fall apart.
ERI antennas are heavy duty and worth the money. Day in Day out.
Antenna technology and design has not changed in 20 or 30 years. Non DA.
> > Besides, Shively antennas suck IMHO. I'm glad to hear you
>
> > guys are getting something better.
>
> You seem to be confused.
>
> TPT is talking about a station he has with an ERI 4 bay on
> it.
> WBUR, the other poster, has a 2 bay Shively which will
> probably be replaced with another Shively.
>
> Personally, I like the Shively antennas, I think they out
> perform ERI's when it comes to the meat... the signal.
> Although I think the ERI's out perform the Shivelys when it
> comes to ruggedness.
>
> Still, personally, my favorite of all the brands is
> Dielectric. I think they have the best antenna going...
>
Everyone has a least one antenna horror story.
I have a dielectric in abox somewhere (panel) that couldn't be installed because the installers felt the thing was ready to fall apart.
ERI antennas are heavy duty and worth the money. Day in Day out.
Antenna technology and design has not changed in 20 or 30 years. Non DA.
> > Besides, Shively antennas suck IMHO. I'm glad to hear you
>
> > guys are getting something better.
>
> You seem to be confused.
>
> TPT is talking about a station he has with an ERI 4 bay on
> it.
> WBUR, the other poster, has a 2 bay Shively which will
> probably be replaced with another Shively.
>
> Personally, I like the Shively antennas, I think they out
> perform ERI's when it comes to the meat... the signal.
> Although I think the ERI's out perform the Shivelys when it
> comes to ruggedness.
>
> Still, personally, my favorite of all the brands is
> Dielectric. I think they have the best antenna going...
>
C
CW
Guest
Re: WHY a new antenna?
> > Besides, Shively antennas suck IMHO. I'm glad to hear you
>
> > guys are getting something better.
>
> You seem to be confused.
>
> TPT is talking about a station he has with an ERI 4 bay on
> it.
> WBUR, the other poster, has a 2 bay Shively which will
> probably be replaced with another Shively.
>
> Personally, I like the Shively antennas, I think they out
> perform ERI's when it comes to the meat... the signal.
> Although I think the ERI's out perform the Shivelys when it
> comes to ruggedness.
I disagree....I had a main with a Shively, the aux which was a mile north and 400ft shorter had an ERI...guess which one had better coverage? if I was out 40+ miles from the tower and turned the aux on, the main got totally covered!
And anytime the ice started to build, the Bird Watcher kept going off on the Shively even with its deicers on 2 days before the ice hit...the ERI?? not a problem....with no deicers too!
A rimshot in the same market went from a ERI to a Shively and the signal in the metro area went to crap....the Shively lasted maybe 3 months and it was GONE! Shively can give you a great optimized pattern but when the rain or ice hits it, the antenna is such a high Q one, SWR goes to *%^& real quick....I remember the printout of my main Shively...it looked too narrow for an FM antenna...
I want something that is FLAT or LOW Q over more than 2-400kHz!
> Still, personally, my favorite of all the brands is
> Dielectric. I think they have the best antenna going..
Well, they bought the Harris line so should we be surprised?? I like Dielectric panels (CBRs) but for a single station rototiller, I would get an ERI and forget it (I would use a Dielectric over an ERI panel/multi station antenna though).
> > Besides, Shively antennas suck IMHO. I'm glad to hear you
>
> > guys are getting something better.
>
> You seem to be confused.
>
> TPT is talking about a station he has with an ERI 4 bay on
> it.
> WBUR, the other poster, has a 2 bay Shively which will
> probably be replaced with another Shively.
>
> Personally, I like the Shively antennas, I think they out
> perform ERI's when it comes to the meat... the signal.
> Although I think the ERI's out perform the Shivelys when it
> comes to ruggedness.
I disagree....I had a main with a Shively, the aux which was a mile north and 400ft shorter had an ERI...guess which one had better coverage? if I was out 40+ miles from the tower and turned the aux on, the main got totally covered!
And anytime the ice started to build, the Bird Watcher kept going off on the Shively even with its deicers on 2 days before the ice hit...the ERI?? not a problem....with no deicers too!
A rimshot in the same market went from a ERI to a Shively and the signal in the metro area went to crap....the Shively lasted maybe 3 months and it was GONE! Shively can give you a great optimized pattern but when the rain or ice hits it, the antenna is such a high Q one, SWR goes to *%^& real quick....I remember the printout of my main Shively...it looked too narrow for an FM antenna...
I want something that is FLAT or LOW Q over more than 2-400kHz!
> Still, personally, my favorite of all the brands is
> Dielectric. I think they have the best antenna going..
Well, they bought the Harris line so should we be surprised?? I like Dielectric panels (CBRs) but for a single station rototiller, I would get an ERI and forget it (I would use a Dielectric over an ERI panel/multi station antenna though).
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