I sometimes get the distinct impression that the corner office doesn’t understand what it takes to keep a radio station on the air and in good repair. It is most often the problems or “issues” that tend to get the most attention. The things that are working well tend to get ignored. After all, how often do you hear a news report about the airliner that landed safely.
Lightning strike, TV tower
When lightning strikes the tower and knocks the transmitter off the air causing major damage and expensive repairs, that is a problem. When lightning strikes the tower and nothing happens, no problem. What is the difference between those two situations?
Grounding strap, FM transmitter site
If the generator starts and runs during every power outage and has done so for the last five years straight, it is obviously a reliable unit, does it need all that maintenance?
Caterpillar 75 KW diesel GENSET
Money spent on preventing undesirable outcomes can be difficult to quantify as disasters and events that do not happen are ill defined. It is difficult to quantify the “amount saved” on something that didn’t or won’t occur. Using past situations is good start, but that only covers a fraction of possible outcomes. In order to invest money wisely, one has to look at the probabilities. If there is an unlimited budget, then the probability exercise should be minimal, however, there is very seldom an unlimited budget.
For example, how much does a back up STL system cost vs the risk of being off the air while the main STL system is being repaired? How often do failures occur, when are they likely to occur and for how long are all good questions. Is there an alternative to a full back up like an IP CODEC? Such a solution would cover all aspects of the STL system including antennas, transmission line, transmitters and receivers.
There are certain FM stations north of here that have neither RADOMES or antenna heaters. Once every two years or so, the antenna ices up and the transmitter folds back due to VSWR. How much of an impact to listeners notice when this happens? If it happened more often, say two to three times a year, would it be wise to invest in some type of deicing equipment?
What is the ownership and management opinion on off air conditions? I have often heard tell “Oh, its only the AM, we don’t mind if it goes off the air.” That is, until it actually goes off the air, then it is a big problem.
Based on my and others experiences, these are the things that will happen at an average transmitter site:
The electric will go off at least once per year for several hours.
The main transmitter will fail at least once every two years.
Lightning will strike the tower at least once per year.
The STL system will fail, at unknown intervals.
At studio sites, these things will occur:
The file server will crash depending on the operating system
The telephone lines and or T-1 service, internet service, ISDN etc will go out
The electric power will go out for several hours
The satellite dish will fail once every two to three years
If there is a tower, it will get struck by lightning
Other site specific things can occur like floods, blizzards, earthquakes, fire, etc.
Money spent on backup systems for those items is good insurance. Not only will the station stay on the air, the on call engineer’s phone will ring less often, which, if you are the on call engineer, should make you happy.
If a full backup is not available, a second transmitter for example, having a good stock of spare parts on hand can mean the difference between an early evening and an all nighter. Keeping good maintenance logs and well documented repair records can point out trends and give a good basis for ordering spare parts.
Repair trends are important. If the same part seems to be going bad over and over, it is time to dig deeper and find the cause of failure.
The old adage “An once of prevention is worth a pound of cure,” still holds true.
We are currently working with one of our clients who needs to rebuild an FM transmitter site. The site is an old house which used to function as a studio. The transmitters are wedged in to various places and the whole place looks like a fire trap. We are working on moving the transmitters to a new building at the base of the tower and installing all ancillary equipment according to good engineering standards.
Transmitter site design has changed somewhat over the years. What may have been good engineering standards in the past have changed with newer transmitter designs and needs. Up until about 1990 or so, most transmitter sites were cooled with outside air. As such, there was often a “filter room” or “air mixing room” with associated blowers and fans for moving air through the building. Older sites often had these features built in as part of the transmitter installation. WPTR’s GE BTA-25 was a good example of this.
Modern solid state transmitters are a little more delicate than there older tube type brethren. Tubes were designed to run hot and had no troubles with temperatures up to 110 to 120 degrees or so. Continental transmitters were famous for this. As Fred Reilly once told me “We’re Dallas and it gets hot here. The manufacturing floor is not conditioned. It don’t matter, 100 degrees, 105 degrees, they just keep on working.” I think he was talking about the assemblers as well as the transmitters.
Solid state transmitter switching power supplies are also somewhat finicky.
A good transmitter site design will incorporate the following:
Good air conditioning. Calculating the AC load for the transmitter waste heat, other installed equipment, as well as the building solar gain. Waste heat is a function of AC/RF transmitter efficiency, which is found in the owner’s manual. If unknown, 50% is a good design standard, in other words, waste heat equals TPO.
Good grounding. A good grounding system is a must for all transmitter sites. This includes lightning and RF grounds. Low impedance paths to a single point ground is a must.
Good power conditioning. Mountain top transmitter sites are susceptible to all sorts of utility company irregularities. Surge protection is a must. Series type are better than parallel.
Good lighting. Nothing is worst than fumbling around in a half lit transmitter room trying to make repairs.
Adequate work spaces and clearances. Electric panels require three feet of clearance from the front. Cabinet doors should be able to swing fully open. All access panels should be, well, accessible.
Adequate electrical system. Pole transformers and service entrance properly sized for load. Backup power. Plenty of work outlets around the room.
Some of these may seem like no-brainers, however, one would be surprised at how transmitter sites have grown over the years. An FM site that may have started with one 5 KW transmitter in 1950 will have been greatly upgraded over the years. Today, that same site may not employ a 30 KW transmitter, full air conditioning, have several tower tenants, etc.
WHUD transmitter site diagram
This is a transmitter site that we redesigned about four years ago. The original site was built in 1958 and had a Gates FM5B as the main transmitter. The electrical service consisted of two 200 amp panels which had been greatly altered over the years. It had an old Onan 65 KW propane generator inside the building. Grounding, Air Conditioning, lighting and work space were all substandard.
The first thing we did was replace the generator with an outdoor unit. That allowed us to remove an interior partition, freeing up a good deal of floor space. Next thing we did was upgrade the electrical service and replace the generator transfer switch. Much of the interior wiring had been altered or added to in non-code compliant ways. All of those modifications were removed or bought up to current electrical code.
A safety grounding ring was installed around the outside of the building and all grounding points were bonded together. Nautel has an excellent guide for transmitter sites which includes lightning grounding and protection for AM and FM transmitter sites. Recommendations for Transmitter Site Preparation (.pdf) and Lightning Protection for Radio Transmitter Stations (.pdf) are available for download from their site. All RF cable outer jackets are bonded to the ground at the base of the tower and the entrance to the building. All the interior equipment is bonded together. Ferrite toriods are placed on all cables going into and coming out of the transmitter cabinets.
With the electrical service upgrade, we added the series LEA surge protector.
Inside view of LEA surge supressor
This site as at the very end of the utility company line and has always suffered from power issues. This unit greatly smooths out the various nasties that get sent our way.
I decided that it was easier to use compact florescent lights (CFL) rather than the long tubes. This site is as the top of a rough mountain road and it is simply easier to carry several small boxes in the cab of the truck than four foot or eight foot florescent light tubes. There is a total of ten 28 watt fixtures in the main transmitter room which light up every nook and cranny.
WHUD transmitter
All of the transmitters and electrical panels were laid out to give working room around them.
The air conditioners were also greatly upgraded and added to the generator load. Prior to this, when the power went out, which was often. the air conditioners did not run and the transmitter room would overheat unless the door was left open. What we previously the filter room became space for tenant equipment. There are a few two way and paging companies still at this site.
Of course, all this work was done while keeping the station on the air as much as possible. There were a few instances of having to turn off to move transmission lines and so on.
The result of all this work is greatly improved site reliability.
If one considers paradise an FM35A. Going through another iteration of blown transmitter fuses for WEBE, Bridgeport, CT. Yesterday, I spent the afternoon examining the transmitter and found several interesting things:
Fresh arc tracks on the PA cavity and PA loading capacitor
The shoes and bars in the high voltage contactor were severely pitted
One of the mains phases (middle) in the high voltage supply appears to be heating up, likely due to a loose connection.
Discolored wire on buss bar
I checked and re-tightened all of the mains connections. Apparently, this is an old problem, as the Allen screw was tight. Interestingly, the fuse that was blown was on the red phase, which is different from what it was last time.
I spent the afternoon filing and sanding off the arc track marks in the PA cavity. It is very important to file flat all sharp points that where the result of arcing. Any sharp points will induce corona. I also filed down all of the contacts in high voltage contactor, which took a fair amount of time. These are soft copper shoes and bars which had so much pitting and carbon I wonder how they didn’t catch on fire. I filed them flat. We were back on the 35A transmitter at full power by 4:30pm.
If this happens again, I will bring my megger out and check the insulation on the wire between the disconnect switch and the HV power supply.
When I left the site at 5:30, I felt like we did some good work.
WSPK is located on North Mt. Beacon, which is the highest point for miles around. It has a fantastic signal. The site is a little difficult to get to, however, especially in the winter. In previous years, the road has been impassable four months out of the year. Some engineers have hired a helicopter to get up there when the snow is deep. For that reason, it is important to keep the equipment in good shape.
WSPK Shively 6810 antenna with damaged top radome
After last February’s snow/rain/ice storm, it was noted that the top antenna radome was missing it’s top. A tower climber was sent up to look at it and it was also discovered that the top bay was bent down and the element was almost cracked in half. A result of falling ice, likely from the big periscope microwave reflector (passive reflector) mounted above it.
WSPK tower
The periscope reflectors went out of service in 2007, but the tower owner did not want to pay to take them down, thus a problem was not being solved. It was decided to replace the 25 year old Shively 6810 antenna with a new one, during which work, the radio station would pay to remove the reflectors from the tower. In exchange for that work, the radio station would then be able to repair and remount the old Shively antenna below the new one, thus having a backup antenna. Problem solved, except for, you know: The actual work.
The tower and the periscope microwave system was installed in 1966, operated on 12 GHz and was used by the Archdiocese of New York to relay their educational television programming from their Yonkers headquarters to the various schools in the Hudson Valley. Sometime around 1975 or so, the FCC mandated that periscope microwave systems could no longer be used due to all the side lobes and interference issues they caused. They were to be taken out of service as soon as possible. The Catholic Church, being a multi millennial organization figured “as soon as possible” meant within the next fifty years or so. Anyway, somebody else needed that frequency, therefore in 2007, they bought the Archdiocese a new digital microwave system.
The problem with the reflectors; they are big. They are also heavy, and present a huge wind area. They are also 300 feet up in the air.
WSPK tower periscope reflectors seen from ground level
Finding a day with lite winds on top of Mount Beacon can be a problem. Luckily, the weather was with us. Still, it took a while to get this work moving along. The other consideration is RFR and tower climber’s safety. There are two digital TV stations, WSPK, several cell carriers, something called “Media Flow,” and a bunch of two way radio repeaters. The main concern was WSPK, the DTV’s and Media Flow since the top of this tower is right in the aperture of those antennas. All either went way down in power or off the air while this work was on going.
Rigging a gin pole and getting it to the top of the tower was a chore. The gin pole needed to be threaded through those torque arms like a needle.
Gin pole
The tower riggers truck had two winches, one a basic 120 volt capstan, the other a hydraulic winch in the bed of the truck with 1/2 inch steel cable.
Tower rigger's truck
The bolts holding the reflectors in place had to be cut with a saw, you can see the tower climber working on the left hand reflector, gives you an idea of size. If this reflector were to fall off the tower, chances are good the major damage and or injuries would result on the ground. Proceed with extreme caution.
Cutting bracket mounting bolt on periscope reflector
Carefully lowering reflector past Shively 6810 FM antenna and Scala PR-950U microwave antenna. During this phase, the tower climbers had to push the reflector out away from those obstacles with their legs. You can see the gin pole at the top of the tower.
Lowering Periscope reflector
Another view:
Lowering reflector
Another view:
Lowering reflector
Almost down to the ground. This measured 15 by 10 feet and ended up weighing 830 pounds.
Reflector almost to the ground
One down, one to go. I can’t believe those gigantic things were at the top of this tower, on the top of this mountain for 43 years and the tower is still standing. This is going to change the appearance of the mountain top from down below. For years, it looked like a pair of mickey mouse ears, now it will only look like a tower. I wonder what the environmentalists will think.
I will make a second post with the antenna pictures as this one is getting a little long.
If a person were to drive south down I-95 through Bridgeport, CT and look off to the left, they would see a 500 foot smokestack for a coal fired power plant. Side mounted on that smokestack is a 6 bay Shively FM antenna. The antenna is more visible when driving south. That would be the antenna for WEBE 107.9 Mhz. This is right down town, therefore, I would imagine this station has no problems with reception.
Bridgeport Power Plant smokestack, viewed from the west
WEBE is a class B FM with a full 50 KW ERP. Most FM’s around here take advantage of a nearby mountain to gain some altitude and thus reduce the TPO a bit. There are several class B stations that run less than 5 KW into a relatively small antenna, but they are way up in the 900 to 1000 foot HAAT range. In this case, the power plant is located right on the Pequonnock River bay, so the AMSL at the base of the smokestack is only 10 feet. This means lots of watts out and a fairly large antenna.
They are using Broadcast Electronics FM35A for the main and backup transmitters. They were installed in late 1986 and are a little long in the tooth.
Broadcast Electronics FM35A transmitter
They run near 12 KV plate supply, about 3.8 amps making 34 KW TPO. That goes into a six bay Shively 6 bay 6813 antenna centered at 475 feet, which makes the HAAT 117 meters.
One of the problems encountered with at site is the smokestack emissions. It seems that a fair amount of mercury comes out to the top of that thing. In the past, this has caused major problems with the antenna shorting itself out and burning up transmission line. Because of this, the entire antenna system, radomes, and transmission line is supplied with Nitrogen from this liquid nitrogen tank:
Liquid Nitrogen Tank
The antenna then intentionally bleeds N2 into the radomes continuously, overpressurizing them, to keep the smokestack emissions out. This type of tank is needed because a conventional N2 tank would last about a day, whereas the liquid tank lasts about 20 days.
The BE FM35A decided to blow a 200 Amp fuse on Friday afternoon:
Blown 200 Amp fuse
I had a BE FM30A that would randomly trip the 200 amp main breaker every once in a while. I could never find anything wrong with the transmitter, it would just come back on and run normally again after the breaker was reset. I even replaced the breaker thinking breaker fatigue. Still happened. In the end, we replaced that transmitter. In this case, I don’t see that happening anytime soon.
BE FM35A heavy iron:
Broadcast Electronics FM35A plate transformer
I would not want to replace this thing, it must easily weight 1,000 pounds.
And rectifier stacks:
Broadcast Electronics FM35A rectifier stacks
12,000 volts DC. That will light up any dirt, dust, piece of fuzz, etc. in the transmitter.
It is one of the more unique FM transmitter sites I’ve ever been to. Every time I see it, I am reminded of that song, Smokestack Lightning. My favorite version of that song is the live recording by the Yardbirds
I followed this a link to this site called “SurvivalRealty.com” and saw this article about what looks to be a former ATT microwave relay site in Utah turned into a residence. The site is much smaller than the former ATT site in Kingston that I profiled in this post. Still, that is a Western Electric tower and those are KS-15676 antennas.
Former ATT microwave site turned into a residence
If I were that guy, I’d take those antennas down a scrap them. Looks like the wave guides are already gone. I might have tried to put some windows in while I was renovating it. It would drive me crazy to live in a house without any windows. I guess if one where waiting for the big one, windows might not be a desired feature of a survival bunker.
I wouldn’t really call it a “communications bunker” though. I’ve been in communications bunkers, they are mostly underground and are much more robust than that building. Still, it is built better than an ordinary commercial building or a regular house. It would take a special person to live out in the middle of nowhere like that.
This is an EIMAC 4CX3500A which came out of a Harris HT5 transmitter. As you can see it the ceramic cracked in half. When I arrived at the transmitter site, the unit was on, full plate voltage, no plate current, no overload lights. I figured it might be something with the tube, so I tried to pull it out, but only the top half came. One of those “Ah ha” moments.
Fortunately, there was a working spare at the transmitter site and we got back on the air relatively quickly. That, in and of itself is amazing considering the building that this transmitter lived in. One of those abandond former studio sites with the transmitter jammed into a back room somewhere. To get to it, one has to dodge pigons, beware of rats and wade through piles of garbage.
It is a little bit hard to tell in this photograph, but there are to “cages” which are the Screen and Grid. The post in the center is the filament/cathode and the top detached part is the plate/anode. In an FM transmitter, the exciter is coupled to the grid, the screen accelerates electrons toward the plate and therefore controls the power, the plate collects the electrons and is coupled to the output stages and the antenna. Good stuff.
Behold, I do not work for Clear Channel. I do not work for Cumulus, or Citadel. The company I work for is not about to go bankrupt, in fact, we have purchased a brand new FM transmitter for the wretched mountain top transmitter site featured here.
Nautel V 7.5 FM transmitter
Am I happy? Oh yes I am. New transmitter = fewer midnight phone calls thus better quality of life for me and my family. A solid state Nautel transmitter means fewer unscheduled trips to the transmitter site and better reliability.
As a result of consolidation and smaller engineering departments, almost my entire work day is now scheduled weeks in advance. One little hiccup in the schedule can throw things off for days, resulting in many apologies, phone calls to reschedule, and general wasted time.
This is a V 7.5 FM transmitter, very likely the last V series transmitter Nautel ever makes. They have moved on to the NV series.
It is replacing the Broadcast Electronics FM5A, which is 24 years old. The BE has been a good transmitter, we lost a few rectifier stacks due to lightning over the years, but over all, it has been reliable and easy to repair when problems did arise. This transmitter will be going into standby service.
Another example from my blown up shit collection, pictures archive:
Burned out harmonic filter, BE FM-30T transmitter
The harmonic filter from a Broadcast Electronics FM-30T. This actually started in the bullet connector to the 3 inch hardline on the output side of the filter.
Burned out 3 inch hard line section
Again, I did not install this myself, someone else did. Cutting 3 inch hard line is pretty straight forward. When using a field flange, the outer and inner conductors are cut flush. Both conductors should be de-burred and filed smooth. It only takes a little thing to start an arc with 30 KW of FM power, so once again, attention to detail is key to avoiding these things.
Fortunately, BE sent along replacement parts for the harmonic filter and the line section was replaced.
I developed these check lists for FM transmitter site based on experience and what needs to be checked, how often it needs to be checked and what else can go wrong. This checklist is for a generic FM transmitter site with a back up transmitter and an RF STL. Every site is different, so some things on this would likely need to be changed or adapted depending on equipment and other facilities.
BE FM20T transmitter
Enjoy!
Weekly Maintenance:
A. Visit site, Check following:
Check critical transmitter values against last logged value
Check forward/reflected power on main transmitter
Check and reset any overloads
Check generator fuel level
Check the STL signal strength level against last logged value.
General check of building, look in all rooms, inspect for damage from vandalism, Leaking roofs, obvious signs of trouble, take steps to correct.
Monthly Maintenance:
B. Visit site, Check following:
Do a full multi-meter log, run backup transmitter into dummy load.
Check line pressure, Check tank pressure and/or desiccant for water
Start and run generator for 5 minutes, check block heater, hoses, belts, oil and antifreeze levels
Calibrate remote control meters with transmitter meters, log it*
Check the tower fence, be sure it is secure and locked.*
Complete Items 3, 4, and 6 under weekly maintenance.
During summer months, be sure the vegetation is cut around building and tower.
Quarterly Maintenance:
C. Visit site, Check following:
Complete 1 through 7 under monthly maintenance.
Check all air filters, clean or replace as needed.
Check frequencies of all exciters, STL receivers, TSL transmitters and log.*
Complete quarterly tower lighting and painting inspection
Bi-yearly Maintenance:
D. Visit site, Check Following:
Complete 1 through 4 under quarterly maintenance.
Clean backup transmitter
Place backup transmitter on air and clean main transmitter.
Yearly Maintenance:
E. Check all licenses and authorizations for accuracy, make sure all license renewal cards are posted and placed in the public inspection file.*
F. Visit site, Check following
Complete 1 through 3 under Bi-yearly maintenance
Complete service of generator
Complete Inspection of tower and antennas, check concrete tower bases, check guy wire anchors, (grounding, turnbuckle safety cable) check property for anything out of the ordinary
Repair driveway as needed
General maintenance that is completed on an as needed basis:
Tube changes on main/backup transmitter.
Sweep antenna with a spectrum analyzer/return loss bridge to make sure it is on frequency and has sufficient bandwidth to pass FM signal.
Look at FM RF mask with spectrum analyzer, check harmonics for proper attenuation.
Sweep transmission line with a spectrum analyzer/return loss generator.
Re-fill fuel generator fuel tank when drops below 1/2
Empty trash, sweep floors, dust.
Paint exterior of building
Replace tower lights*
Paint towers*
*These are FCC inspection items, pay close attention if you do not want a fine.
The .pdf version can be downloaded here. I’ll to an AM directional check list next week.
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution
Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin
...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner
Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19
Open Mic