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Lightning protection for WLAN links

More and more wireless LAN links are being installed between the transmitter and studio.  Often these links are used for network extension, remote control, site security, VIOP telephony, and sometimes even as a main STL.  These systems come in several flavors:

  • Moseley LAN link or similar system.  Operates on unlicensed 920 MHz (902-928 MHz) band.  Advantages: can use existing 900 MHz STL antennas, can work reliably over longer distances, transmitter and receiver located indoors.  Disadvantages: slow, expensive
  • ADTRAN TRACER or similar system with indoor tranceivers and coax fed antenna systems.  Operates on unlicensed or licensed WLAN frequencies.  Advantages: fast, transmitter and receiver located indoors, can be configured for Ethernet or T-1/E-1 ports.  Disadvantages; expensive
  • Ubiquiti Nano bridge or similar system where tranceiver is located in the antenna, the system is connected via category 5/6 cable with POE.  Operates on unlicensed or licensed WLAN frequencies.  Advantages; fast, relatively inexpensive.  Disadvantages; equipment located on tower, difficult to transition base insulator of series fed AM tower.
  • Ubiquiti Rocket or similar system where the antenna and tranceiver are separate, but the transciever is often located on the tower behind the antenna and fed with category 5/6 cable with POE.  Operates on unlicensed and licensed WLAN frequencies.

For the first two categories of WLAN equipment, standard lightning protection measures are usually adequate:

  • Good common point ground techniques
  • Ground the coaxial cable shield at the tower base and at the entrance to the building
  • Appropriate coaxial type transmission line surge suppressors
  • Ferrite toroids on ethernet and power connections

For the second two types of WLAN equipment, special attention is need with the ethernet cable goes between the tower and POE injector or switch.  Shielded, UV resistant cable is a requirement.  On an AM tower, the shielded cable must also be run inside a metal conduit.  Due to the skin effect, the metal conduit will keep most of the RF away from the ethernet cable.  Crossing a base insulator of a series excited tower presents a special problem.

The best way to get across the base insulator of a series excited tower is to use fiber.  This precludes the use of POE which means that AC power will be needed up on the tower to power the radio and fiber converter.  This my not be a huge problem if the tower is lit and the incandescent lighting system can be upgraded to LEDs.  A small NEMA 4 enclosure can house the fiber converter and POE injector to run the WLAN radio.  Some shorter AM towers are no longer lit.

Another possible method would be to fabricate an RF choke out of copper tubing.  This is the same idea as a tower lighting choke or a sample system that uses tower mounted loops.  I would not recommend this for power levels over 10 KW or on towers that are over 160 electrical degrees tall.  Basically, some 3/8 or 1/2 inch copper tubing can be wound into a coil through which a shielded ethernet cable can be run.  Twenty to twenty five turns, 12 inches in diameter will work for the upper part of the band.  For the lower part, the coil diameter should be 24 inches.

In all cases where CAT 5 or 6 cable is used on a tower, it must be shielded and the proper shielded connectors must be used.  In addition, whatever is injecting power into the cable, ether POE injector or POE switch must be very well grounded.  The connector on the shielded Cat5 or 6 cable must be properly applied to ensure the shield is grounded.  A good video from Ubiquiti, which makes TOUGHCable, on application of connectors to shielded Cat5 cable is here:

In addition to that, some type of surge suppressor at the base of the tower is also needed. Tramstector makes several products to protect low voltage data circuits.

Transtector APLU 1101 series dataline protector

Transtector APLU 1101 series dataline protector

These units are very well made and designed to mount to a tower leg. They come with clamps and ground conductor designed to bolt to a standard copper ground buss bar.

Transtector APLU 1101 series dataline protector

Transtector APLU 1101 series dataline protector

There are various models designed to pass POE or even 90 VDC ring voltage.

Transtector APLU 1101 series dataline protector

Transtector APLU 1101 series dataline protector

This model is for POE. The circuit seems to consist mostly of TVS diodes clamping the various data conductors.

As more and more of these systems are installed and become a part of critical infrastructure, more thought needs to be given to lightning protection, redundancy and disaster recovery in the event of equipment failure.

On being responsible

No two days are alike. Sure, there are days that are similar in nature, office work, filing, FCC compliance, etc.  However, there is always something different, some new problem, person, fault, error, client, site or situation to deal with.  It helps to be well versed.

So, when the tower climbers started climbing a 1,000 foot (304 meter) tall tower to find a damaged section of transmission line, I thought; Just a routine day.

Even when they encountered a hornet’s nest at 50 feet (15 meters) AGL, still, fairly routine:

Tower climber applying bee spray to paper wasp nest

Tower climber applying bee spray to paper wasp nest

Tower climber A received a nasty bee sting to his left arm. He climbed part way down the tower and is in the lower part of the picture hugging the tower face. Tower climber B moved up and killed the nest with Wasp and Bee killer.  All is well and work resumes, right?  Except, no.  Tower climber A is apparently allergic to bees.  He states he is not feeling well and his arm begins to swell up.  He comes down the tower and I start looking for Benadryl.

Now, we have a problem.  This is a mountain top tower site, there is a long dirt road with a locked gate at the bottom of the hill.  There is almost no way an ambulance will be able to find its way up here.  The tower climber says the he has not been stung in many years.  I also notice his face is beginning to swell up.  Right, so lock the door, in the truck and get to the bottom of the hill as fast as possible.  It took about five minutes, but at the bottom of the hill, we were in a much better position if things got worse and an ambulance needed to be called.  Fortunately, his condition was the same, so we drove to an urgent care facility were he was treated.

Benadryl, something else to add to the go bag.

Always keep ahead of the situation.  Even if we drove to the bottom of the hill and his symptoms completely disappeared, it still would have been the right decision.

The Shukhov Tower

A very interesting bit of broadcasting history in Moscow may disappear forever.  Designed and built by Vladimir Grigoryevich Shukhov, the Shukhov Tower was completed in 1922.  Since that time it has served as a AM broadcasting and later and FM broadcasting tower.  In the picture, one can see what looks like a massive FM panel antenna at the top.  According to this website: www.shukhov.org, the tower is in very poor shape and is slated to be demolished.

The tower itself is described as 160 Meters (525 feet) tall, hyperboloid steel lattice structure. The design is unique in that it is very strong, yet uses approximately 60-70 percent less steel than a comparable four legged structure like the Eiffel tower.  An amazing feat of engineering for its day, when everything was calculated and drawn by hand.

Shukhov Tower, Moscow, FSR

Shukhov Tower, Moscow, FSR.

The antenna is a little hard to discern, however, it looks like a horizontally polarized six or eight around 4 bay FM antenna. Could also be low band VHF TV.

Shukhov Tower antenna

Shukhov Tower antenna. Courtesy Wikipedia

Unfortunately, time is running out and little or nothing is being done to protect the steel structure from the elements. The last paint job was more than twenty years ago. The land it currently occupies has some value, and there is talk of putting up a high rise development in its place.

Article from the New York Times; An engineering landmark faces demolition in Moscow.

There are lots of videos on youtube and pictures from the wikipedia article.  It is an interesting bit of history, if it can be saved it will be a very close run thing.

North Adams Tower Collapse

High winds seem to be the culprit in the collapse of two towers in North Adams. According to the Motorola system technicians, it happened at about 12:30 am Sunday morning, which is when all their link loss alarms started going off.  The larger, self supporting tower broke from it’s mounting plate and tipped over into the smaller guyed tower next to it. Effected are WUPE-FM and W226AW (WFCR New England Public Radio) as well as NEPR new station WNNI which has not officially signed on.

Cellular service for ATT, Verizon and Sprint/NEXTEL were all knocked off line as well internet services and E911 dispatch.  Those services are coming back on line, with temporary modular cell units en route. News report from WWLP channel 22, Springfield, MA:

Here are some pictures:

North Adams Cell Tower

North Adams Cell Tower

WUPE-FM antenna on the ground

WUPE-FM antenna on the ground

WUPE-FM antenna

WUPE-FM antenna

WUPE-FM STL dish

WUPE-FM STL dish

Base of WUPE-FM (formerly WMNB) tower

Base of WUPE-FM (formerly WMNB) tower

WNNI antenna

WNNI antenna

WUPE-FM WNNI and W266AW transmitter building

WUPE-FM, WNNI, and W266AW transmitter building

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

Tower base mounting plate, apparent failure point

Tower base mounting plate, apparent failure point

Tower base mounting plate

Tower base mounting plate

Tower Base Mounting Plate

Tower Base Mounting Plate

For pictures of the towers during happier times, refer to this post: Filtering for co-located FM transmitters.

Restoration work is underway with WUPE-FM expected to return to air at low power by Monday afternoon.

Update:

WUPE-FM was returned to air at low power by about 1pm on Monday 3/31.  We took an unused Shively 6812 antenna that was tuned to 94.1 MHz and retuned it to 100.1 by cutting 1/4 inch pieces from the end of the elements until it was on frequency.  It took a bit of doing, but with a network analyzer, we were able to get it to 1.2:1 SWR with symmetrical sidebands.  Running 600 watts, it covers the city of license and then some.

WUPE-FM temporary antenna

WUPE-FM temporary antenna, Shively 6812

The STL antenna is a survey antenna mounted on the side of the building. In this configuration, with the leaves off of the trees, we are getting about 250 uV signal, which is pretty good.

WUPE-FM temporary STL antenna

WUPE-FM temporary STL antenna

The site is now crawling with insurance investigators, cell site technicians, North Adams fire department, Berkshire County Sheriff’s officers, tower workers, etc.  After we finished this work, we cleared out to make more room for everybody else.  Estimated restore time for W266AW is Wednesday 4/2.

Planning for the replacement tower is already in progress, I’d expect it to happen fairly quickly. The next step for the broadcasters is to put up a 70 foot utility pole and get a full powered antenna for WUPE. This should happen in the next two weeks or so. That will serve as the temporary facility until the new tower is constructed.

The NASH: WNSH, Newark, NJ

Lately, I have been working at a site in West Orange, NJ connecting various parts and pieces and thought that this was interesting:

WNSH 94.7 MHz, Newark, NJ main antenna (top)

WNSH 94.7 MHz, Newark, NJ main antenna (top)

That is the main antenna for WNSH, 94.7 MHz Newark, NJ, aka “Nash-FM.”  Below that is the backup antenna for WEPN-FM (98.7 MHz), WQHT (97.1 MHz) and WFAN-FM (101.9 MHz).  More on those stations later.

WFME studio building

WFME studio building

This is the WFME studios, located off of NJ Route 10.  It is kind of hard to see the call letters behind all those trees and whatnot.  There is an older picture from 1999 floating around, which shows the studio building in better condition.  This is a better angle:

WFME studio

WFME studio

I believe WFME is still originating its programming here, now being broadcast on WFME 106.3 MHz, Mount Kisco.  I had to use the facilities there, the interior is like a way back 80’s time machine, which is kind of cool.  If I owned a radio station, I would go for the 70’s office decor; dark wood paneling, shag carpets, bright blue bathroom tile and avocado green appliances, but hey, that’s just me.

WNSH backup antenna, WFME-TV antenna

WNSH backup antenna, WFME-TV antenna

This is the WNSH backup antenna, mounted on top of a UHF slot antenna for WFME-TV.  There is an LP TV antenna mounted there also, but I don’ t know who it belongs to.  Overall, it is an interesting transmitter site on “First Mountain” in West Orange, NJ.  Also located here, WFMU-FM, an old ATT microwave site, now owned by American Tower and several cell carriers.   In other words, it is just like most other mountain top transmitter sites, except there is a shopping plaza across the street.

I gave a listen to the NASH while driving there.  For where it is, it seems to have a pretty good coverage area.  As for the music, well, I am not sure how a Manhattenite will relate to Tracy Byrd’s “I’m from the Country” wherein:

Everybody knows everybody, everybody calls you friend
You don’t need an invitation, kick off your shoes come on in
Yeah, we know how to work and we know how to play
We’re from the country and we like it that way

Being from upstate NY, I get it.  Perhaps the Manhattan salary man will too.  There are no DJ’s on air quite yet, just music, some commercials and a few “Nash-FM” liners that sound slightly distorted.

Zonecasting; the Technical Details

I saw this a item many weeks ago, however, had not had time to look at it until now.  Geo Broadcasting Solutions has filed Petition for Rule Making (RM-11659) based on a system divides the coverage area of major stations into smaller zones allowing for ad targeting of specific audiences.  They have coined the term “Zone Casting” to describe the scheme. It is covered by two US issued patents filed by Lazer Spots, LLC: 20120014370 and 20110065377.  After a look at these two patents, it seems there are three possible ways to accomplish this Zone Casting Scheme:

  1. In the first described method, the main transmitter is broadcasting area wide and all the zone transmitters are muted.  An inaudible signal is transmitted to all units, the main transmitter is then muted and the zone transmitters turn on and transmit localized content.  After the local information is transmitted, the zone transmitters mute and the main transmitter resumes broadcasting.
  2. In the second described method, the main transmitter and the zone transmitters are broadcasting area wide information.  The main transmitter ceases broadcasting area wide information and the zone transmitters begin broadcasting localized information.  At the end of the localized information the main transmitter and zone transmitters transmit area wide information.
  3. In the third describe method, the main transmitter and zone transmitters are broadcasting wide area information with “capture ratio pattern.”  The main transmitter initiates an alteration, temporarily becoming a zone transmitter.  The zone transmitters then transmit localized content.  After the localized content, the main transmitter becomes a main transmitter again.

All of the transmitters are linked to the studio via digital STL systems, content for the zone transmitters is distributed via IP network.  The transmitter frequencies are synced with GPS, similar to FM on channel booster stations.  Method number three includes possibly switching the transmitter output to a lower gain and or lower height antenna.

Zone Broadcasting Conceptual Diagram

Zone Broadcasting Conceptual Diagram

Of the three methods, the first system will result in the fewest interference issues.  No matter which method is used, there will be interference issues between the zone transmitters and or the main transmitter where the signal strengths are equal and the audio is 180 degrees out of phase.  These can be moved around slightly by adding delay to the audio signal, but they will always be present.  More about Same Frequency Networks (SFN) and Synchronized FM signals can be found here.  While the zone transmitters are transmitting dissimilar localized information, standard capture effect rules apply.

The system has had limited testing in Salt Lake City, Utah (KDUT) and Avon Park, Florida (WWOJ), which according to the filing and comments, went well.

Geo-Broadcasting is applying to conduct a full test with WRMF in Palm Beach, FL.  The expected installation will include up to 22 zone transmitters.

Conceptually, tightly targeted advertising is not a bad idea.  Advertisers like it because they perceive a better return for their dollar.  The cost of such a system is not insignificant. Transmitter site leases run $1-2K per month, leased data lines, equipment, installation work, equipment shelters, etc will likely run several hundred thousand dollars or more.

If it gets approved by the FCC, it will be interesting to see how it works and whether or not the system is financially justifiable.

 

North East Commerical Radio Antennas and Towers

NECRAT logo

NECRAT logo

Or NECRAT for those who have been around the internet for a while. Many, if not most of you will know Mike Fitzpatrick’s NECRAT website which features many pictures of radio transmitter sites around the country (not just the Northeast).

Even before I began blogging, I checked NECRAT often for interesting pictures of many different transmitter sites.

If you are one of the few who has not visited his site, go and check it out: http://www.necrat.us

PBS Frontline: Cell Tower Deaths

Interesting video (part 1 of 3) about the large numbers of Cell tower deaths in the last eight years:

Watch Cell Tower Deaths on PBS. See more from FRONTLINE.

There are two kinds of tower companies, those that have been around for a long time and do things right, and those that hire subcontractors who are minimally trained and take shortcuts. The reasons for this are the same and we hear them over and over again in all aspects of this business; budgetary constraints, time constraints and what, who me?

The rest of the videos can be found at PBS.org:  Frontline: Cell Tower Deaths

Written story from Propublica: In Race For Better Cell Service, Men who climb towers loose their lives.

Tower light malfunction

We were notified that the WFAS-AM tower lights were out, thus, it was time to investigate. This problem was easy to find. Upon removing the water proof cover on the tower light flasher box, I found this:

SSAC melted tower light flasher, damaged by lightning

melted SSAC B-KON tower light flasher, damaged by lightning

As soon as loosened the screws on the cover, I smelled the unmistakeable odor of burned electronics and plastic.   I disconnected the flasher and covered the photocell, which turned the side markers on.  Of course, the top flashing beacon was dark, therefore, it was time to report the outage to the FAA.  The nation wide number to report tower light outages is (877) 487-6867.  That number is for an automated system, however, eventually it leads to a live person.  Since the new reporting system was established, the only required information is the tower ASRN.  From that information, the operator will access a data base and have all the required information to issue a NOTAM.  In the past, many questions were usually asked; what is the nearest airport, how far away is the airport, how tall is the obstruction, what is the position, etc.  Therefore, things have become slightly easier than before.

Once the outage is reported and a NOTAM is issued, the tower owner generally has fifteen days to correct the problem.

So, you call this work?

A trip to the WSPK transmitter site on a pleasant day, or, one could say, another day at the “office.”  Tower painting season is here, I’ll post some more about that later.  This is a nice set of pictures from the top of Mt. Beacon, in Beacon, NY.

Hudson Valley looking north from Mt. Beacon

Hudson Valley looking north from Mt. Beacon

South Mount  Beacon with the old fire tower:

Mount Beacon looking south at the old fire tower

Mount Beacon looking south at the old fire tower

Tower farm; two TV stations, Media Flow, one radio station, three translators, several cell carriers, one paging company, some government two way gear, and a few microwave relays.  The 320 foot guyed tower in the center holds the main (top) and backup (bottom) antennas for WSPK:

Mount Beacon Tower Farm

Mount Beacon Tower Farm

Tower climbers ascending a 320 foot tower.  This picture (and all the others as well) was taken with my HTC smartphone camera, proving the old adage, sometimes it is better to be lucky than good:

Tower workers on 320 foot guyed tower

Tower workers on 320 foot guyed tower

View from the ATC site at the very top of North Mount Beacon of the tower workers painting the top of the tower:

Tower workers painting torque arms on 320 foot guyed tower

Tower workers painting torque arms on 320 foot guyed tower

Another view from the ground:

Tower workers on Mt Beacon tower

Tower workers on Mt Beacon tower

All in all, not a bad day.

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