One thing that I like about the radio engineering job, every day is different from the last, at least when doing fieldwork. Access to transmitter sites can be a challenge, especially in the Winter months. Last Wednesday, I was doing work for WBEC in Pittsfield, MA. Their FM transmitter site is atop Mahanna Cobble in the Bousquet Ski Area. The summit is about 1,800 feet AMSL and since the terrible rains last month, not been accessible by vehicle. No worries though, somebody built this nice chair lift for us to use:
Bousquet Ski Area chair lift going downhill
Going down! I forgot to take pictures on the ride up.
Bousquet ski area chair lift
The steep part of the hill.
Top of the hill radio towerAmerican tower site top of Bousquet ski area
One of two towers, both owned and managed by American Tower Corporation. This is the older tower that has the radio station, somebody’s translator, some paging and two-way stuff, and sprint PCS. The other tower is to the right, out of the picture and holds cell carriers.
View to the north over the valley, WBEC-AM’s two tower directional array can be seen in the lower left hand side of the picture.
View to the north
WBEC-FM’s transmitter, it’s in there somewhere:
WBEC Nautel VS 2.5 transmitter
Polyphasor surge protector has seen better days. It suffered some serious damage and was removed from the circuit. Now, it makes a convenient home for rodents. Reduce, reuse, recycle:
Polyphasor surge suppressor
Something is missing…
N2 regulator with nothing to do
Now where did I put that Nitrogen tank? The site needs a little work and that’s okay, we came to work and get paid.
It was a hot day, it was a cold day. The tube transmitter was running, the solid-state (HD-1) transmitter was off the air. The books show that the company has deep pockets, but the accountant has short arms. And so it goes. In a sordid, yet familiar tale of leaping three-quarters of the way across a river, the builders of this transmitter site seemed to think of everything except the cooling requirements for a 35 KW FM transmitter.
Instead of installing real commercial AC units, someone decided that 34,000 BTU window units were the way to go. At one time, there were eight of those units, all single phase 240 volts sucking down gobs of power and freezing up when the outside temperature dropped below 40°F. This was always a problem but became more so when we took over the maintenance of this site. When there was a full-time engineer, his time, apparently, could be wasted running back and forth turning the window units on or off in the winter as required. Now that a contract company is doing the work, it becomes cost prohibitive to require such things.
Therefore, the time had come to make a change. To that end, six of the 34,000 BTU window units were removed from the building. Two of the existing holes in the wall were used to create an emergency cooling system, consisting of a 4,292 CFM fan and a couple of shutters. Two other holes were used for the new air conditioners and two holes were blocked up. The remaining two window units were left in place in the combiner room, which is a separate cooling zone.
Bard 5-ton wall mount AC unit and cooling fan shutter
The new ACs are five-ton wall-mount Bard units. These are three phase and should be more than enough to keep the transmitters cool. Here is how I arrived at that conclusion:
The entire building load when the main transmitter is running at full power, without the transmitter room air conditioning, is 60 KW.
All of the building loads except the transmitters go through a single-phase panel.
The load on the single phase panel is 10 KW, thus the transmitter load is 50 KW (this 10 KW is mostly the single phase AC units in the combiner room)
The TPO is 32 KW, therefore the transmitter is generating 18 KW of waste heat.
One watt-hour = 3.412 BTU of energy, thus
18,000-watt-hours equals 61,416 BTUs
One ton = 12,000 BTU, thus
61,416 BTU ÷ 12,000 BTU = 5.118 tons
That will take care of the main transmitter waste heat. The HD transmitter generates another 4,000 watts of waste heat or 1.37 tons. The combiner is in another room and doesn’t factor into the calculation. The rest of the equipment is inconsequential, adding up to less than 100 watts.
The solar gain is more difficult to calculate, as it is based on the building structure, the type of construction, and the heat gain (loss) through the walls and doors. This building is concrete block, insulated, and has no windows. It is unshaded, however, it is painted a light color. All in all, the solar gain should be less than two tons on a hot day. Therefore the total AC load should be 8.25 tons or less.
Bard 5 ton wall mount AC unit
All that is left now was to install the things. Just pull up the truck and use a crane to lift them in place, except, no; that plan won’t work. This is the transmitter site at the power plant and the 138 KV lines overhead precluded any lifting with a crane. We instead had to build ramps and move things around on large-hand trucks. One unit is installed on the rear of the building, the other on the front. It required several days to make the ramps and four people to muscle the things into place.
The bottom air intake holes needed to be cut out for the new units. Cutting into the concrete block while the BE FM 35A was running proved to be another challenge. We used several sheets of plastic, shop vacs, and extra air filters on the transmitters to keep the concrete dust out of the PA cavities and motor bearings.
Plan B cooling consists of a 4,292 CFM Venturi fan mounted on the rear wall of the building. The fan is controlled by a ceiling-mounted thermostat set to 95 degrees. If the AC’s fail, the ceiling temperature will rise and the fan will turn on.
Transmitter site emergency cooling fan
The room volume is about 3600 cubic feet, therefore this fan will change the room air about once every 60 seconds or so. It is not the best plan to move humid, potentially dirty outside air through a building, but it it keeps the station on the air while the main AC units are being repaired, then so be it.
The entire system went on line last week and is working well.
This is cute. A small (VS allegedly stands for “Very Small”) integrated 2,500-watt FM transmitter. This one we just finished installing as a backup transmitter for WSPK, on Mount Beacon, New York.
Nautel VS-2.5 FM Transmitter
This site has a Nautel V-7.5 as the main transmitter. That unit is very reliable, however, this transmitter site is non-accessible 4-5 months out of the year due to ice and snow. The last time we had an off-air emergency due to a crippling ice storm, it took an entire week to clear away all the downed trees so we could gain access to the site via snowmobile. As such, every system needs dual or even triple redundancy. The lack of said redundancy has led to several prolonged outages in the past.
WSPK signal flow diagram
Last year, we were finally able to install a backup antenna after 63 years without one. This year, it is time to upgrade the rest of the backup equipment. The new auxiliary transmitter is connected directly to the auxiliary antenna via a five-port coax switch. This allows for the use of the dummy load for testing when we are present, but removes a potential failure point in the coax switch. There have been at least two incidences of the disk jockey accidentally transferring the transmitter into the dummy load when taking transmitter readings. Hopefully, this configuration will be fairly idiot-proof. I am making an interlock panel that will prevent both transmitters from being on the air at the same time.
Nautel VS 2.5 connections
This site is a work in progress.
The backup processor is at the transmitter site, the main processor is in the rack room at the studio. This works well because the main processor occasionally looses its mind and needs to be rebooted. It would be a significant pain to drive all the way up to the transmitter site just to reboot the processor. It might not happen at all during the winter. The backup processor has no mind so it is not an issue.
The VS transmitter is attractive because it has a built-in exciter that accepts composite, AES, or IP audio. The exciter also has a built-in Orban processor as an option. Thus, if it really hit the fan, we could use the LAN extender to get the audio to the site. Further, it could be addressed by any studio in the company WAN. Which is cool, when you think about it.
Nautel continues to crank out innovative, dependable products and there is nothing wrong with that.
As alluded to in the previous post, I spent a fair amount of time at Mt. Mansfield last month. It is the highest point in the state of Vermont, topping out at 4,393 feet (1,339 M). At the top, there is a large transmission facility that is home to WCAX-TV, WPTZ-TV, WVPS, WEZF, several low-power TVs, NOAA weather radio, etc. Next door, Vermont Public TV is housed in a separate building. Here are a few pictures and descriptions. First of all, Mount Mansfield is the home of the Stowe Ski area. They own the access road to the top of the mountain and are quite proud of it. In the summertime, the toll for a carload of people is $26.00.
Mount Mansfield Toll Road gate
The transmitter building is below the actual peak. This is one of the few transmitter sites that is manned 24/7, as such there is a working kitchen, bathroom, bunk rooms, and so on. I’d imagine it gets pretty deary up there in the wintertime, but perhaps not.
Mount Mansfield transmitter building
The transmitters are located along a long hallway. WEZF and WVPS share a room, and WCAX and WPTZ are in open bays as are the low-power TVs. NOAA weather radio and some other government transmitters are located in the garage.
WCAX digital TV transmitter
All of the TV transmitters are new because of the recent conversion from analog to digital transmission. WCAX is noted as channel three, which was their analog channel, they actually transmit on channel 22 with a power of 443 KW ERP.
WPTZ transmitter
Like WCAX, WPTZ was on channel five, it is now transmitting on channel 14 with 650 KW ERP.
The site is backed up by two 1.2 MW diesel generators, which can be paralleled with the commercial power grid, if needed, during peak demand times. These generators also provide backup power for the Stowe Ski area. There is a 50 KW back up back up generator that runs all of the emergency transmitter cooling equipment if the two main backup generators fail.
Mount Mansfield generator
All of this generating equipment requires a lot of fuel.
Transmitter building and fuel storage tanks
The TV and FM broadcast antennas are located just below the peak
Mount Mansfield TV and FM antennas
I don’t recall which TV station belongs to which antenna. The FMs are combined into the four-bay, three-around panel antenna, this includes WVPS’s HD radio signal.
Mount Mansfield from the top looking west
From the very top looking west into the aperture of the TV antennas. I only stood there for as long as it took to get a good picture, then departed. Off to the left of this view is the antenna for Vermont Public TV.
Mount Mansfield Vermont Public TV antenna
The transmission lines go down the hill on a large ice bridge. An absolute necessity as the rime ice can sometimes accumulate several inches.
Mount Mansfield Ice Bridge
Tower base, is the location of the highest RF concentration, according to the TV engineers. I only lingered here to snap a few quick photos.
Mount Mansfield tower base
All of the STL antennas are mounted to the side of the transmitter building next to the living quarters.
Mount Mansfield STL antennas
On top of all that, as if that weren’t enough, there is the view. I would also comment a bit on the weather. In some cases, the site can be completely engulfed in a grey dull fog bank one minute, then the wind changes direction, the sun comes out and you see this:
Mount Mansfield morning
I can think of worse things.
I regret that I didn’t have a better camera with me as several of the pertinent pictures came out blurry. All of these pictures were taken with my cellphone camera, which works well when it works. It is also very convenient because it is almost always with me and I don’t have to remember to bring another gadget. However, it this is going to be a semi-serious endeavor, I will have to take some of my earnings from these scribblings and buy a good camera.
