FM transmitter site – Page 10

Backup cooling

One of the issues that I have seen at many transmitter sites is inadequate cooling. Time was, when mostly tube transmitters were in use, a simple fan connected to a thermostat was all that was used to cool most transmitter sites. Even then, however, that setup was lacking for several reasons.

Those reasons are:

The amount of cooling provided was limited by the amount of heat in the outside air. On cool winter days, this is not a problem, but on hot, sticky summer days it could be.
No removal of humidity from the transmitter room was possible. This often leads to excess oxidation, corrosion of metal parts, and so on.
No matter how much filtering was used, bugs, dirt, and other debris were sucked into the fan, making transmitter room cleaning a chore.

With solid-state transmitters, air conditioning is required. Solid-state transmitter devices are far less rugged than tubes when it comes to heat. In a high-heat situation, a tube transmitter will keep running until its control circuits malfunction, or it catches on fire. A solid-state transmitter will crash long before either of those things happen.

Air conditioners should be adequately sized for the heat load plus a little extra. That information can be found in a previous post: A tale of two air conditioners.

As we all know, equipment malfunctions. When an air conditioning system goes bad at a transmitter site, things start to happen fast if there is no backup. That is when a backup cooling fan can save the day. A good rule of thumb for sizing a cooling fan is to exchange the total volume of the transmitter room every two minutes accounting for resistance from louvers and intake openings.

3200 CFM cooling fan, WHUD transmitter site

This fan is connected to a 120-volt contact on a thermostat attached to the ceiling of the transmitter room. The thermostat is set to 90 degrees, which gives a good bit of headroom for the air conditioners to maintain the room temperature while turning the fan on before the room gets too hot. It is also important to monitor the room temperature via remote control. Having an alarm contact connected to the fan thermostat is also a good idea.

There is no such thing as too much backup. Installing a louvered cooling fan affords a little bit of extra insurance.

WVTQ Mount Equinox, Vermont

The transmitter for Vermont Public Radio, WVTQ 95.1Sudbury is located on Mount Equinox, near Manchester Vermont. Mount Equinox is one of the better mountain top transmitter sites to get to as it has a good access road, no jeep trails through the woods or ski lifts, etc. The Summit is 3,580 feet (1,175 m), which is the third-highest peak in the green mountains. On a nice day, the view from the top is spectacular:

The southern view with US Route 7 cutting through the valley below.

WVTQ is a part of VPR’s classical music network. They had a Nautel VS-1000 that had developed issues with the directional coupler. This unit was repaired and re-installed:

WVTQ Nautel VS-1000 transmitter, Mount Equinox, Vermont

The transmitter has a 7/8 EIA flange on the back, which had an elbow, then an adapter to a type N connector all unsupported. My boss felt that perhaps that perhaps too much weight on the EIA flange caused the crack in the directional coupler.

WVTQ transmitter racks and STL equipment

The transmitter site used to be in the basement of the hotel, but as that building no longer exists, it was moved over to the former RADAR site. The RADAR site consists of four 80-foot towers arranged in a square around a building. These towers now support two-way radio equipment and the like

WVTQ transmitter site, Mount Equinox, Vermont

Your author (left) with Rich Parker of VPR discussing the finer points of GPS antennas.

Ladder to the top of one of the towers.

Hang Glider's view, east side pulloff, Mount Equinox, Vermont — Hang Glider’s view, east side pulloff, Mount Equinox, Vermont

View from the turn-off on the east side of Skyline Drive. Known as “hang glider’s view” with good reason. This is on the saddle that connects little Equinox with big Equinox.

On a nice day, such as yesterday, it is very pleasant. When the road is covered in ice and snow, not so much.

Burk Autopilot

The old version of the software, that is. I like the graphical interface, just one glance is all that is needed:

I have not had a chance to fool around with the newer version, the screen shots on the Burk website look a little bit different.

The setup and programming of macros is pretty easy; power/pattern change times, Pre-sunrise, and post-sunset functions, automatic tower light monitoring, AM Directional Antenna readings, and automatic transmitter restoration routines. If programmed correctly, the software can eliminate many of those late-night/early-morning phone calls, which is always a good goal.

The hard restart

Sometimes there is just no way around it, especially with some modern equipment:

This Nautel VS2500 transmitter got all cranky after lightning struck the tower (or nearby) on Friday night. Thunderstorms in February are not unheard of, but they are unusual, at least in the Northeastern United States.

Nautel VS2500 FM transmitter, WBEC-FM, Pittsfield, MA

Anyway, the transmitter would not reset or restart via remote control, therefore, we had to ride the chair lift to the top of the hill and pull the plug to reset its logic and start over again.

At least the trip up to the transmitter site was scenic. We had to wait a day for the winds to calm down, but all in all, not a terrible day. Did I mention the scenery?