Installations – Page 3 – Engineering Radio

There is a place on Earth called Meddybemps

I might not know that if I hadn’t been there installing a TV transmitter. We installed this GatesAir VAXTE-2 for Maine Public Broadcasting’s WMED-DT.

GatesAir VAXTE-2, WMED-DT Meddybemps, Maine

After the old Harris Platnum transmitter was turned off, the client got a call from the cable company across the border in New Brunswick. Apparently, they take the off-air signal for their cable feed of PBS in New Brunswick.

We also installed a VAXTE-6 at Mars Hill for WMEM-DT.

GatesAir VAXTE-6, WMEM-DT, Mars Hill, Maine

I was reading through the SBE 2023 salary survey and noticed that those engineers who work in Radio and TV make more money than those who do just radio. My experience is that TV is more technically challenging because there are many more building blocks that go into the end product. ATSC has several layers of complexity starting with video and audio codecs. Then there are various transport methods, PSIP (Program information) tables, aspect ratios, degrees of definition, video and audio bit rate considerations, and muxing, which occur before the Transport Stream gets to the exciter.

DTV ATSC 1 modulation analysis; 8VSB eye pattern

One thing I will note, TV is acronym-heavy. There are many combinations of letters and abbreviations. I can work on a list of things that I have learned, but one of the most important measurements for the quality of the over-the-air signal is MER, which stands for Modulation Error Ratio. MER is measured in decibels and low MER usually indicates some distortion problem.

Once the program material hits the exciter, the process is similar but there are a few noted differences. TV transmissions are 6 MHz wide vs. 200 KHz for standard FM. In order to minimize distortion, the signal needs to be precorrected by the exciter for linearity. HD Radio does the same thing to a degree. High-band VHF and UHF stations tend to use slot antennas. These are high-gain broad-banded systems that are generally very simple. The FCC stipulates that spectrum mask filters be used to limit out-of-channel emissions. During the installation process, the filters must be measured and proofed to comply. In addition, the harmonics need to be measured down to -120 dBm because most of them fall in the wireless data and mobile phone spectrum and we know how those folks can be.

Like other segments of the broadcast engineering profession; TV is struggling to find competent technical staff, so if you are willing to learn new things, consider doing some work in television.

Mars Hill also has many of these giant things:

I’ve never seen one up close, and I will say they do make a fair bit of noise when it is windy. I also noticed that air density makes a difference in the noise levels. When it is cooler or more humid, the noise level goes up. There are twenty-eight 1.5 MW GE wind turbines that generate enough electricity to power 18,000 average homes annually. Maine has several wind turbine farms in various parts of the state. I believe Mars Hill was the first, completed in 2006.

Cellular work on a skirted tower

Cell carriers generally do not like working on AM towers. It is out of their comfort zone and adds a layer of complexity to the project. However, sometimes they don’t have a choice, mainly when there is an existing site and they need to make changes. We have also had mixed results with tower contractors employed by various cell carriers. In one incident, a contractor showed up and re-tensioned the guy wires breaking all of the porcelain insulators. Another time, a contractor showed up to install footings 10 feet away from the tower and ripped up all the ground wires. One tower climber found one of the skirt wires was in his way, so he cut it off with a hack saw.

Those experiences demonstrate that it is far less expensive to have somebody on site while tower contractors are doing installation work on any skirted AM tower. And so it was today.

AT&T 5G sector assembled waiting for lift

This tower has two AM stations diplexed as well as two FM translators combined into one Nicomm antenna. We did before measurements on the AM stations using an OIB-3. Once the installation is done, we will do the after-measurements and then assist the licensee with any FCC 302 filings if the base impedance has changed significantly.

With each lift, I went out to the base of the tower and made sure that the skirt wires were clear of the mounting brackets and not touching anything else. The tower crew was Russian speakers. When they asked if the transmitter was still on, which was kind of comical (he motioned to the skirt wire, made like he was grabbing it, then jerked around like he was being electrocuted). I had to wrack my brain to try and remember: Передатчик выключен. The literal translation is “Not working.” The difference between “working” and “not working” is one consonant at the beginning of the second word which is pronounced soft for off and hard for on.

This site was the subject of a previous post: A tale of five signals.

FLX20KFAX50K+HD

Greetings from the Roxborough tower farm, a place with roots. It is slightly northwest of Philadelphia, PA, and is home to many TV and FM stations. The public road that cuts through the tower farm is called Domino Lane because if one tower falls, they all fall. A comforting thought to those that live in the vicinity I am sure.

View from the residential neighborhood next to the site

The reason for the visit; this rather nice GatesAir FLX20 transmitter:

Newly installed FLX20+HD, WRNB Philadelphia, PA

I must admit, I am growing rather fond of these transmitters. This unit is being installed because the station had to move from its old site, just down the hill. The tower owner is taking down the tower and building due to the age of the tower. Thus, it was moved into the KYW-TV building. If Wikipedia is to be believed, KYW-TV is the oldest TV station in Philadelphia, signing on in 1932.

The site is still being built as we were installing this transmitter. These days, the electricians are having supply chain problems like everyone else. There were delays getting the large electrical panel board and other necessary things for the build-out.

Cooling system high point, sight glass, and air purge valve

Overall, the installation went well. This system is using flexible hoses for the coolant loop. We have installed two of these liquid-cooled transmitters with 1 1/2 copper pipe. These days, copper pipe is expensive, so most are opting for flexible hose installation.

Topping off the pump station after 50/50 fillup. After the initial system fillup, it takes a while for all of the dissolved air to come out of the Heat Transfer Fluid (HTF). The extra steps with a liquid-cooled system are worth it, especially if the station is running HD. With the HD carrier on, the transmitter efficiency is 54% AC to RF. With a TPO of around 15 KW, that is a whole lot of heat that needs to be dissipated during operation. It is much cheaper to pipe the heat outside to a heat exchanger than to use several tons of AC to remove it from the room.

Overall, this was a fun project.

New transmitter building for an old station

UPDATE:

What the site looks like now with the old building removed:

Putting the finishing touches on another transmitter site rebuild, this time in central NY. This station for many years used this rambling white residential-looking structure for both the studio and transmitter site:

Former studio and transmitter site for WDLA, Walton, NY

Unfortunately, over the years, the building has deteriorated beyond economical repair. A few years ago, the studio facility was moved to a new location in town. Now the transmitters are being moved to this repurposed cellular building:

Former NEXTEL building, now WDLA AM/FM transmitter site

This was purchased used from a local crane company, which had dozens of them on their lot after NEXTEL was absorbed by Sprint. During the permitting process with the town, they referred to it as a “Circular Use.”

They are actually nice buildings, coming prewired with a 200 amp single phase service, two working Bard HVAC units, ready-made coax entry ports, etc. My only complaint (so far), is the light switch timer. I like the idea, the lights get switched off automatically and are not left on for months at a time when nobody is at the site. However, the timer only goes up to 2 hours. Thus, when we were doing the installation work, periodically there would be an audible click, then everything would go dark. Not terrible.

There are also two other FM stations that have an STL transmitter here.

STL equipment for two additional stations

All in all, an enjoyable project.