FM Translator pole size?

FM does it with frequency!
Post Reply
User avatar
Qs23
Posts: 28
Joined: Sat Mar 31, 2012 5:18 pm
Location: Kalamazoo, MI
Contact:

FM Translator pole size?

Post by Qs23 » Fri Dec 23, 2016 11:33 am

Hey all,

So I'm an IT guy who's been tasked with setting up an FM translator. (Don't ask, I brought it upon myself to broaden my horizons) Now the antenna setup that we're using is a two bay BEX-TFC2KN setup. We're going to be mounting this on a cell tower next to the studio building. There's already an old vertical dipole setup at the top of the tower that needs to be taken down. (Old police antenna) So we thought that would be the prefect place for the new FM Translator. The problem is that the two bay setup is only going to be mounted to the tower at the bottom.

I was thinking a 21' 3in diameter Schedule 40 galvanized steel pipe.

So, my question is, would that be enough? Too much? too little? I'm turning to you guys, because I have no clue who else to ask.

User avatar
Deep Thought
Posts: 3187
Joined: Thu Mar 20, 2008 9:23 am
Location: La Grange, IL
Contact:

Re: FM Translator pole size?

Post by Deep Thought » Fri Dec 23, 2016 11:57 am

What is the weight and windload of the antenna? 21 feet of 3" may or may not work depending on how you attach it to the tower.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

Lee_Wheeler
Posts: 79
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

Re: FM Translator pole size?

Post by Lee_Wheeler » Fri Dec 23, 2016 5:17 pm

I am going to guess that this is a tapered, self supporting tower. The 3" pipe should work OK but you will need to have brackets fabricated to support the pipe both top and bottom. There are some off the shelf adjustable standoff brackets that you can source through Sitepro that will work with most tapers.

http://www.sitepro1.com/store/cart.php? ... list&c=632

Scroll down the page to get to the tapered tower versions if that is what you have.

...Lee

User avatar
Deep Thought
Posts: 3187
Joined: Thu Mar 20, 2008 9:23 am
Location: La Grange, IL
Contact:

Re: FM Translator pole size?

Post by Deep Thought » Sat Dec 24, 2016 12:11 am

Lee_Wheeler wrote:The 3" pipe should work OK but you will need to have brackets fabricated to support the pipe both top and bottom.
Qs23 wrote:The problem is that the two bay setup is only going to be mounted to the tower at the bottom.
Being only attached at the bottom could very well be an expensive problem.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

TPT
Posts: 653
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: FM Translator pole size?

Post by TPT » Sat Dec 24, 2016 8:14 am

Sure this isn't a BEXT antenna? Can't find this model. Anyway, the first question is how much does each bay weigh? A small antenna, weighing 4 or 5 pounds may not pose much of a problem--then the crucial factor is the weight of the pole.

A two-bay antenna would normally be spaced one wavelength apart or around 9 feet, depending on frequency. If you are mounting the antenna on a the top of a guyed tower, you could get away with a short pole, placing the bottom bay near the top of the actual tower. If this is the typical self-supporting tower used for cell, then you want a longer pole to keep the bottom bay at least 5 feet above the top of the tower. Which would require a longer and heavier pole. Unless you can leave a longer section of the pole below the top of the tower--to allow more of it to be attached to the tower, you may want to change plans & go with a single bay antenna, putting construction costs toward a bigger transmitter.

My experience is that most cell phone companies want extensive and expensive analysis be done before they allow an antenna to be mounted on their tower, which make these towers impractical for low-budget projects like a translator.

User avatar
kkiddkkidd
Posts: 515
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: FM Translator pole size?

Post by kkiddkkidd » Sun Dec 25, 2016 9:57 am

Oh and I forgot to mention... Stay far, far away from cell towers unless that is your only choice. I once had a client that had a number of CPs on corporate owned cell towers and they found out very quickly that it was a bad idea. Structural studies, short (expensive) list of acceptable tower contractors, huge insurance requirements just for engineers to enter the compound, etc, etc. Privately owned 2-way or broadcast towers are typically magnitudes cheaper to install on, maintain and probably lease.

Anything larger than a 1-bay antenna may require the rent of multiple carrier levels.

And then there is that little LTE interference problem that some FM freqs cause.... This can be remedied but should be taken into consideration.

Make sure you know exactly what you are getting into before signing a lease.

Regards,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

rich wood
Posts: 99
Joined: Mon Jan 24, 2011 10:56 am
Location: Madison, WI
Contact:

Re: FM Translator pole size?

Post by rich wood » Sun Dec 25, 2016 3:24 pm

Kevin Kidd is right on the mark. Cell towers have some very expensive and difficult unknowns that can crop up. Avoid if at all possible.

User avatar
NECRAT
Site Admin
Posts: 2939
Joined: Sat Nov 17, 2007 9:13 pm
Location: Taunton, MA
Contact:

Re: FM Translator pole size?

Post by NECRAT » Sun Dec 25, 2016 9:01 pm

TPT wrote:Sure this isn't a BEXT antenna?
This is a Bext Antenna. The FCC code is BEX. It's a dual arrow style antenna.
http://www.necrat.us

"Arguing with an engineer is like mud wrestling with a pig. After a couple of hours, you realize the pig likes it"

TPT
Posts: 653
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: FM Translator pole size?

Post by TPT » Mon Dec 26, 2016 8:39 am

Bext.Com needs a company name that is more Google friendly.

The only weight spec. I can find is 50 pounds for antenna AND shipping crate. I'm going to guess the antenna is probably under 15 pounds. They do indicate it will clamp on a 1" pole. If you can get on the top of this cell tower, I would be inclined to go with a single bay at the top of a 1" pole, about 15' long--with most of the pole attached at several points below the top of the tower. With the antenna maybe 5 feet above the top part of the tower. Then spend the money saved on installation for more transmitter power to compensate for the loss of antenna gain.

The 2 bay would be about unity gain, while the single bay would be half power. So if your translator ERP is 100 watts, you would need about 100 watts into the two bay antenna, or 200 watts into the single bay antenna--at the top of the tower. More than that from the transmitter, as some power is lost in the coaxial cable.

User avatar
Qs23
Posts: 28
Joined: Sat Mar 31, 2012 5:18 pm
Location: Kalamazoo, MI
Contact:

Re: FM Translator pole size?

Post by Qs23 » Mon Dec 26, 2016 3:06 pm

Hey All,

Sorry I didn't get back sooner, Christmas called.

The link to the antenna is: http://www.bext.com/broadcast-antennas/tfc2k/

I checked the spec sheet and a 2 bay version of this antenna has a wind load of 136 lbs @ 100 mph.

The tower is right next to our studio. And it used to be owned by the cell company, but the ownership actually transferred to us this year. Don't ask me how, that died with the previous owners of the station.

And according to our paperwork, we've got to go directional with this setup due to both 1st and 2nd adjacent neighbors. So, the calculations done for compliance with the 2 bay setup that I stated, so we're going with the 2 bay setup. I don't think I can get around that.

I'm off today, but I can get a picture for you guys tomorrow.

TPT
Posts: 653
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: FM Translator pole size?

Post by TPT » Mon Dec 26, 2016 6:11 pm

This isn't a directional antenna. It could be --but you would need to have Bext set it up on a test range & supply the paperwork showing the pattern meets the specs in your CP. Don't think they can do that.

SWR can do that--they have a test range--but costs start to climb again.

FCC will accept an antenna with a "standard" pattern. Translator near me uses the SCALA CA5 to meet this requirement. There are others, with different patterns, FCC just requires that they be mounted in accordance with the manufacturer's directions.

User avatar
Deep Thought
Posts: 3187
Joined: Thu Mar 20, 2008 9:23 am
Location: La Grange, IL
Contact:

Re: FM Translator pole size?

Post by Deep Thought » Mon Dec 26, 2016 9:08 pm

"we've got to go directional with this setup"

You've now wandered into the realm of consultants and really need to cough up some specifics about this translator. You can't just guess at this if you plan to be able to get this to work right, or at all.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

TPT
Posts: 653
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: FM Translator pole size?

Post by TPT » Tue Dec 27, 2016 7:41 am

Then again, if this is a conventional self-supporting "cell" tower, you can use that to your advantage to meet the requirements for a directional antenna. Use the tower to block signal towards the stations you need to protect. By side-mounting the antenna, instead of on a pole. Still requires a pattern study, unless you use something like the Scala CA5--side mounted with the back end of the tower towards the station you need to protect.

Still need that consultant

Lee_Wheeler
Posts: 79
Joined: Sun Jul 24, 2016 1:53 pm
Location: Kansas City

Re: FM Translator pole size?

Post by Lee_Wheeler » Wed Dec 28, 2016 7:17 pm

If the Construction Permit calls for a directional antenna the exact specifications of the make and model of the antenna should be specified in the permit and in its underlying application. It will need to be followed exactly as it was applied for. Any antenna other than an "Off the Shelf" directional antenna will need to be range tested at the factory so as to be contained within the pattern envelope and the manufacturer will provide a proof of performance with the antenna as well as very detailed mounting instructions. There will need to be a certified statement from an "engineer" that the antenna was assembled and installed as specified and another certification from a surveyor that certifies that the orientation of the antenna, relative to true north, is as was specified in the proof of performance.

The engineering certification is a bit loose, that can be done by a staff engineer at the station or even someone who has assumed a supervisory role in the installation but that certification must made be under penalty of perjury. The surveyor certification must be from a registered professional surveyor.

Prior to the antenna manufacturer doing the range testing they will need to know the exact make and model of the tower. The exact elevation where the antenna is to be mounted. The number of, size of, and location of any coax segments that run through the aperture of the antenna to other antennae that are mounted above the antenna. If there is a pipe mount that will be used as a standoff from the tower they will need to know the pipe dimensions and how far off of the tower the pipe will be mounted. I have put the latter requirement ball in their court and requested that they specify the mounting standoff instructions in the proof of performance which gives them an additional variable to work with so as to make the pattern fit the envelope. They will also need to know the exact orientation of the tower relative to true north which means not one but two trips to the site for the surveyor.

Although helpful, it isn't really necessary to have the original technical consultant come in to supervise the project but a chat with him or her could make things much easier for you.

...Lee

TPT
Posts: 653
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: FM Translator pole size?

Post by TPT » Thu Dec 29, 2016 6:59 am

With a translator, if you use an "off-the-shelf" DA antenna, you only need to certify that it was installed according to manufacturer's (and C.P.) directions. Unlike full-power, where you need a surveyor, etc.

I'm still not clear here whether they have a CP here, or are only in the planning stage...As Lee describes, the C.P. would specify the antenna, which is why the initial talk about using that Bext antenna leads me to believe they are still in the planning stage.

About two years ago, one of my part-timers was taking a journalism course at a local community college. She board-opped for us on football nights & worked for the local weekly newspaper. That school had just received their C.P. for a low power on my third adjacent. She introduced me to the journalism prof. & her student aide working on the project. He was looking for equipment in a B & H catalog, and for transmitters on the internet.... Intervention definitely needed--I set them up with a Nautel VS300 & SWR antenna & built the studios.

I suspect the best solution here--as a number of us suggested, that they find a good engineering consultant to design this project.

Post Reply