A story about TV transmitter maintenance should be about how to fix a TV transmitter, but not this one. Today’s new TV transmitters are nearly bullet-proof. Their high efficiency doesn’t require as much air conditioning, but even the highest-efficiency new TV transmitter will overheat inside an unventilated transmitter building on a warm day after the air conditioning fails. It can happen. Trust me.

New transmitters are modular, and once-mysterious technical adjustments such as shoulders are simple and mostly automatic. But, there’s more to keeping a TV transmitter on the air than fixing one when it gets sick, especially in the middle of nowhere. Modern transmitter problems are more often the result of its environment.

Transmitter Facility Types

There are three types of transmitter facilities. One is the in-house transmitter, inside the same clean building with the station’s studios, operations and offices. Advantages are that it’s a part of the station’s home, it shares its power source and HVAC system with the station, staff is nearby, and the station usually owns the tower. The downside is dead birds and ice falling from the tower to the station parking lot below.

The second type is remote in-town or at the local antenna farm, sometimes on someone else’s tower, also called co-locating. The downside for engineers is the surface-street distance from the station studios. But, it can be a good excuse to eat lunch somewhere different when duty calls. Otherwise it is nearly as convenient as in-house without the falling natural debris. It often can include a shared tower and/or transmitter building and a secure perimeter, significantly reducing the management load for tenants compared to sole ownership.

The third type is out-of-town, possibly far out of town and likely in the boondocks by nearly all definitions. Accessibility is usually measured by the vehicle ground-clearance needed to get to the transmitter. It could be on a mountain or in a cow pasture. The minimum requirements are a tower, a building, and power for the HVAC, transmitter, digital 2-way STL, and the tower lights. Facilities in the middle of nowhere are also lightning magnets. Good grounding saves trips.

Common utility services are available in every town, but seldom in the boondocks. No secondary utility power source? Install a generator with a generous fuel supply. No land line, cell service or the internet? Use a digital 2-way STL to connect to the studio. No running water? Wait, what?

The rarest utility at truly remote transmitter sites is running water. TV transmitters don’t need running water, and remote sites usually don’t have sinks or sewers. But, the building air conditioning cooling coils need to be regularly washed and rinsed with gallons of water. If not, the AC system will eventually trip a pressure switch, cycle on and off, and/or shut down altogether.

Cell Sites vs. Broadcast Sites

For the past decade, I’ve been the contract transmitter engineer for a 5-transmitter site SFN TV station, now in repack. The station leases tower space on two cell towers, one FM tower, one on another station's TV tower, and built and owns a 600’ tower at the 5^th site. These sites are where I’ve lived the reality of remote TV transmitters sites.

Most shared out-of-town remote sites are owned by third-party companies in the vertical real estate business, such as American Tower or Crown Castle, who combined own approximately 80,000 of an estimated 200,000 communications towers in the US.

Third-party sites, towers and access to them are maintained by the owner and they already have local utility power. Typically, tower clients provide their own pre-fab building. The least expensive buildings found at most cell sites are known as communications equipment shelters. They are designed to house electronic communications equipment, and often come with electrical wiring and dual AC units. The AC units are the Achille’s heel.

The most common natural threat to transmitter facilities in the boondocks is all the pollen and dirt in the country air.

Pollen is a sticky organic material. When pushed or pulled through a condenser coil, some pollen sticks to the capillary tubes and fins, as will some bugs and bug parts. The build-up ultimately results in the loss of thermal transfer of heat to outside and thus no cold air. It also makes the Freon pressure rise which trips pressure switches. Eventually, pressure switches can freeze and not trip, disabling the first warning of a coming catastrophic unit failure. The only fix for a dirty coil is to physically clean it.

Cleaning the Condenser Coil

About 6 technicians from three different HVAC companies have serviced the station’s five transmitter sites, and none could figure out how to clean a coil without running water, even when I threw money at them. As the number of emergency service calls grew, the HVAC techs would throw their hands up, say it needs cleaning and they can’t do it.

At that point I did what any good broadcast engineer who gets the first call when something important breaks would do after hearing “I can’t” too often. I improvised.

The challenge was that cleaning a coil requires a flood of fresh water not available at any of the sites. I bought my own flood in water-filled, 5-gallon plastic gas cans. Then I used a 5-gallon plastic paint bucket with a 2 Gpm submersible water pump in it, connected to a garden hose. Fill the bucket, plug in the pump, keep it full and it sprays fresh water like an outdoor faucet. It’s a simple $150 solution.

It seemed logical that power spraying with water would clean the coils, and at first it appeared effective. The submersible pump put out more water than a small electric powered sprayer uses, and it made the coil look clean to the eye. But over time, power spraying lost its effectiveness and pressure switches started tripping on hot days. It was time to consult YouTube.

Bard makes AC units commonly found in prefab communications buildings and used at our transmitter sites. Bard has posted a coil cleaning video on the internet. The video describes the recommended method to clean a coil using a liquid coil cleaning solution.

Air conditioning condenser coils need cleaning on a regular basis because organic particles in the air tend to stick to the coil, and the boondocks can be organic particle central. There is a right way and a wrong way to clean a condenser coil. One wrong way is to use a shop vac with a brush attachment because it is ineffective and can bend the delicate condenser fins, adding to heat transfer issues.

Another wrong way is to use a pressure washer. Not only can a pressure washer spray bend condenser coil fins, but the pressure of the water will pack the particles tighter, thicken the goop make it and stick better to the coil and fins. That’s what happened to us. The coil looked cleaner, but it wasn’t. We needed chemical help.

Safe Coil Cleaning

Step 1: Turn off AC system power and shut off the outdoor disconnect.

Step 2: Remove the outside vent panels that protect the coil and inspect the inside. 

Step 3: Put on your safety goggles and gloves, pour liquid cleaner into hand-pumped pressure sprayer and mix appropriately.

Most liquid coil cleaners require at least 50% dilution with water, and the best way to apply the diluted solution is with a hand-pump pressure sprayer. Liquid condenser coil cleaners are acidic or alkaline. Either way, the liquid is nasty and serious. It burns skin and has fumes. Always wear goggles and gloves when using the cleaning solution and never spray it in the wind. Cleaner chemicals will burn skin, stain concrete and dissolve asphalt. Always rinse the solution away until completely clear.

Step 4: Before spraying the cleaning solution, wet the coil with clean rinse water first. 

Step 5: Spray the cleaner solution from the pump-sprayer into the condenser fins from a distance of just a few inches, top to bottom, corner to corner.

Step 6: Wait about 5 minutes for the solution to foam and lift the organic debris, and rinse until all foam is completely gone. About 10 gallons of water will rinse a 5-ton Bard unit.

Bard AC units are quite common on prefab communications equipment shelters. A Bard unit pulls fresh air in through the sides of the unit and pushes it through the coil where it exhausts out the back of the unit. The larger organic material collects on the fan-side of the coil where the air is forced in. Spraying and rinsing from the outside-in works best.

Most other air conditioners work the opposite, pulling fresh air through the coil and pushing the warm air out. Pulling air in through the coil collects the bigger organic material on the outside of the coil. Cleaning it is most effective when sprayed and rinsed from the inside-out.

Inside-out or outside-in, effective coil cleaning is a dangerous, delicate job involving nasty chemicals with fumes. Use protection, take care, and rinse thoroughly.

Plan B

This issue has made me look more closely at other cell sites. Most use Bards. About half have added external air filters on each side where the air is pulled in and a roof over the unit to keep the cardboard filters relatively dry. When researching this story I also discovered several magnetic devices to hold filter media on the sides of Bard AC units where the fan pulls in fresh air. Haven't tried the magnets yet, but external waterproof filter media would clearly be the least expensive and easiest-to-service method to diminish condenser coil clogging.