Trends In Technology: Build a Reliable Transmitter Site

February 1, 2015

Every radio or TV station engineer wants to have a reliable transmitter site. Specifically though, what is meant by reliable? Naturally we want any transmitter site to be trouble-free; we also want it to run consistently and be predictable. On a personal note, no one wants to be called out in the middle of the night to fix transmitter site problems. With fewer and fewer staff responsible for more and more remote sites, we seek to minimize unscheduled, emergency trips. We want reliability, consistency and predictability at any transmitter site; the achievement of those qualities is what this article is about. Much of this material has been covered in the pages of Radio before, but these points can never be emphasized enough. 

Shelter

As an engineer dealing with remote sites, it isn’t just the equipment that you need worry about; all manner of things can happen to an unattended site sitting out in the middle of nowhere. Having a poor shelter, for example, can lead to many other problems.

Creatures of the wild are often attracted to the shelter and warmth of transmitter buildings. Aside from having to clean up big messes left from mice that sometimes build nests in equipment, a more serious problem can come from the fact that rodents have a tendency to eat wire insulation. This can lead to open circuits, short circuits or other issues that show up if water happens to touch the wires for some reason. Rats and mice will often die right in the transmitter building, leading to further messes and awful smells. Snakes are another matter. I haven’t had much experience with them; however, I did once clean a tube-type transmitter that had been invaded by a snake. It had come in through a transmission line conduit and decided that the HV power supply was the place to be, with predictable results. That was nearly 30 years ago, and I can still remember how bad it was.

Water is another common issue at a transmitter site. An obvious problem is leaks through the ceiling that drip right in to the top of your transmitter or rack. A less obvious issue is condensate from an air conditioner with plugged drains that manages to drip into a transmitter or rack. The worst scenario with water is flooding, of course.

A large part of site management is mitigating the problems I’ve mentioned so far. If you are sharing space with other tenants, especially those with outside walls, you’ll be challenged to keep varmints out because many of the ingress points are outside of your control. All you can really do is exercise your rights in the lease and have the landlord keep these problems in check. On the other hand, if the site belongs to you, I recommend the following:

Carefully block all potential ingress points for mice, rats and snakes. This includes windows, holes that pass coaxial cable or conduits outside, vent holes and door seals.

Look for water leaks while it is raining. Sometimes you can find evidence of leaks after the rain has passed and things have dried out, but it is much easier to see where drips are originating while they are actually happening.

When air conditioners are installed, plan for appropriate drainage. Having drip pans underneath air conditioners is fine, but if the drains get blocked the condensate water can end up in places that you don’t want. Avoid placing pans or drain lines over transmitters and racks if at all possible.

Flooding. The prevention of flooding is something you can really only do when the site is being constructed from the ground up. For AM sites, if a site is built in a flood plain, plan for a height that will accommodate at least a 100-year flood level. Include the building, ATUs and tower bases. As for mountaintop FM sites, consider the possibilities of landslides that could damage your building from below (washouts) or from above (mudslides).

A major part of building a reliable transmitter site is anticipation of things that could go wrong. The four items I’ve just mentioned are predictable and can be addressed ahead of time.

Alternate power sources

It’s only after you’ve generated your own power for more than several hours that you begin to realize how difficult it can be. Your local utility does it 24/7/365 so of course, they have it figured out (for the most part).

If you are installing a new generator, your design issues are size and runtime. If the transmitter site already exists and all loads are wired to the same distribution panel, then clearly the generator will need to be large enough to power all the loads. If you are starting from the ground up, you might want to consider having an emergency panel, which is one that is sourced from the automatic transfer switch, but does not power all the loads.

Fuel storage is always a difficult problem because one must balance the maximum anticipated runtime against the cost of the fuel, the cost of storage vessels and even fuel maintenance. Always remember that the situation causing the power outage is also likely to cause problems for your local utility and the fuel company you use. If you normally maintain enough fuel to run 36 hours (for example) and find later that the road to your transmitter site is closed and cannot be reopened for several days, then trouble is at hand. I’ll offer up one piece of advice here: “Get it all going in.” You’ll find it far easier to get money to install a larger generator and/or more fuel storage when the project is in the design phase than you will if you try to get everything upgraded after the fact.

Clearly, regular generator maintenance is crucial to your peace of mind, and nothing solidifies it more than testing the generator under load. During this test, all the various elements of the system get used in an “emergency” situation. Predictability is what is important here. You need to know what is going to happen when there is a power failure at the site.

During the test, look for the following:

•    After the transfer occurs, your normal air-chain should power up and all user-selected configurations should be remembered. It should require no intervention.

•    All UPSs should have no problem running on generator power.

•    Any remote control signaling regarding the generator should be active. Likely you’ll have “generator running” status along with “generator transferred to load” status.

•    All IP network equipment restored and automatically connected. E-mails regarding transfer should have gone out and been received by the far end devices.

•    Upon re-transfer, all elements of the air chain should continue without problems, obviously. The generator should have a cool-down period after the re-transfer of 10 to 15 minutes.

•    Remote controls should indicate the generator is off-line.

      There will always be some question as to length of the load-test. From my own experience, I would recommend at least 4 hours. Just remember: The longer it goes, the more confidence instilled. If you schedule regular infrared testing of your electrical system, it’s a good idea to do so while testing the generator under load, because it allows you to test the integrity of the electrical connections that are not normally used.

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