We are in the process of installing an R&S 40 KW liquid-cooled FM transmitter. My first comment; these are well-built units. A quick look at the machining of the parts indicates attention to detail is a key design feature.
As the price of electricity continues to rise, liquid-cooled transmitters for this power level make a lot of sense.
This installation is for Pamal Broadcasting’s WHUD, Peekskill, New York. The site has undergone major upgrades in the last few years. The original 1958 World Tower Utility 80 was replaced a year ago with this Valmont 60X394. Two cell carriers, two translators, and several E911 services are now colocated on the tower.
The transmitter building is also the original cinder block structure from 1958. When it signed on, the station had a Gates FM5B 5 KW transmitter, an RCA BFA-7, 7-bay horizontally polarized antenna with an ERP of 20 KW. In 1970, that antenna was changed out to a 6-bay circularly polarized ERI with a Harris FM20H transmitter, increasing the ERP to 50 KW. As of now, the station has a 4-bay ERI SHP-4-A-C main antenna and the TPO is 28 KW for the same 50 KW ERP. As the station’s power increased, the building became a little bit smaller than optimal. We needed to rearrange some equipment to gain space for the pump station and step-up transformer.
Rhode Schwarz recommended installing a step-up transformer for the incoming AC mains. The power supplies run most efficiently with 400 volts AC.
We decided to reuse the ERI switchless combiner left over from the Nautel V-40 installation. There are two Nautel V-10 transmitters with a hybrid combiner that are to be used as a backup. We won’t be running this as a combined transmitter operation, it is a way to save money rather than install a separate 3-inch coax switch. I will build a simple control panel to move the combiner position either all the way up (THR9) or all the way down (V-10s).
Working on the liquid cooling system. I used a core drill to make the supply and return lines to the outdoor heat exchanger. I made sure that I had the shop vac (with a HEPA filter) running while drilling so that all of the concrete dust was captured. That stuff can get everywhere and has a bad tendency to destroy motor bearings. Whatever plant made these blocks in 1958, they used some hard material. It took a while for my masonry drill to get through them.
Update: This post is from several years ago (January 31, 2018), however, I did a fairly major revision and added a lot of information, so I am bumping it to the top of the pile. The header picture is from the Myat facility in Mahwah, New Jersey.
Installing transmitters requires a multitude of skills; understanding the electrical code, basic wiring, RF theory, and even aesthetics play some part in a good installation. Working with rigid transmission line is a bit like working with plumbing (and is often called that). Rigid transmission line is often used within the transmitter plant to connect to a four-port coax switch, test load, backup transmitter, and so on. Sometimes it is used outside to go up the tower to the antenna, however, such use has been mostly supplanted by Heliax-type flexible coax.
We completed a moderate upgrade to a station in Albany; installing a coax switch, test load, and backup transmitter. I thought it would be interesting to document the rigid line work required to complete this installation. The TPO at this installation is about 5.5 KW including the HD carriers. The backup transmitter is a Nautel VS-1, analog only.
This site uses a 1 5/8-inch transmission line. That line is good for most FM installations up to about 10-15 Kilowatts TPO. Beyond that, 3-inch line should be used for TPOs up to about 30 Kilowatts. Above 30 KW TPO, 4 inch or greater line is required. There are a few combined FM stations that are pumping 80 or 90 KW up to the antenna. Those require 6 inch or greater line. Even though the transmission lines themselves are rated to handle much more power, reflected power often creates nodes along the line where the forward power and reflected power are in phase. This can create hot spots and if the reflected power gets high enough, flashovers.
This brings up another point; most rigid line comes in 20-foot sections. There are certain FM frequencies that require different lengths due to the aforementioned nodes that fall along the 1 wavelength intervals. If one of those nodes happens on a flange, that could create problems.
Frequencies between 88.1 and 95.9 MHz, use 20-foot line sections
Frequencies between 96.1 and 98.3 MHz, use 19.5-foot line sections
Frequencies between 98.5 and 100.1 MHz, use 19-foot line sections
Frequencies between 100.3 and 107.9 MHz, use 20-foot line sections
TV frequencies are much more complicated. The large channel width and much larger spectrum use means that close attention needs to be paid to line section length. Since low-power TV and translators may need to change frequency, those stations often use Heliax instead of rigid line.
Working with rigid line requires a little bit of patience, careful measurements, and some special tools. Since the line itself is expensive and the transmission line lengthener has yet to be invented, I tend to use the “measure twice and cut once” methodology.
For cutting, I have this nice portable band saw and table. I bought this particular tool several years ago and it has saved me hours if not days of work at various sites. I have used it to cut not just coaxial line and cables, but uni strut, threaded rod, copper pipe, coolant line, conduit, wire trays, etc. If you are doing any type of metalwork that involves cutting, this tool is highly recommended.
There are now Lion battery types of bandsaws which are certainly more portable than this. Still, the table with the chain clamp makes work much easier and the cuts are straight (perpendicular), which in turn makes the entire installation easier.
The next point is how long to cut the line pieces and still accommodate field flanges and inter-bay line anchors (AKA bullets).
The inner conductor is always going to be shorter than the outer conductor by some amount. Below is a chart with the dimensions of various types of rigid coaxial cables.
When working with 1 5/8 inch rigid coax, for example, the outer conductor is cut 0.187 inches (0.47 cm) shorter than the measured distance to accommodate the field flange. The inner conductor is cut 0.438 inches (1.11 cm) shorter (dimension “D” in the above diagram) than the outer conductor to accommodate the inter-bay anchors. These are per side, so the inner conductor will actually be 0.876 inches (2.22 cm) shorter than the outer conductor. Incidentally, I find it is easier to work in metric as it is much easier to measure out 2.22 CM than to try and convert 0.876 inches to some fraction commonly found on a tape measure. For this reason, I always have a metric ruler in my tool kit.
If you do not have a handy chart, you can estimate the inner conductor length by measuring the inner bay anchor from the insulator to the first shoulder. Then multiply by two.
In this case, the measurement from insulator to shoulder is 11/16th of an inch (17.5 mm). If Clamp On Flange adaptors (AKA field flanges) are being used, don’t forget to account for the small lip (usually less than 1/16th of an inch) around the inside of the flange where the outer conductor is seated. If you are using unflanged couplings instead of field flanges, then you can disregard this.
The next step is de-burring. This is really critical at high power levels. I use a copper de-burring tool commonly used by plumbers and electricians.
One could also use a round or rat tail file to de-bur. The grace of clamp-on field flanges is they have some small amount of play in how far onto the rigid line they are clamped. This can be used to offset any small measurement errors and make the installation look good.
The weather affects many things. When the weather improves, outdoor projects like tower work can be completed. When the weather is terrible, we may need to do extra work restoring broadcast signals. Today, I am looking at Hurricane Lee, in the North Atlantic basin. Historically speaking, September is the month when we get Hurricanes in the Northeast.
As of this writing, it is too early to be concerned about Lee. Hurricanes can be very unpredictable and there is a good chance the forecast will change many times over the next week or so. That being said, this time of year is a good time to call the fuel companies and top off the generator tanks since winter is coming in a few months anyway. As the situation develops, I may need to dust off the pre-storm checklist.
The basic pre-storm checklist looks something like this:
96 hours or more before the storm: Schedule fuel deliveries for generators, and top off oil and water as needed. Test generators under load if possible. Check UPS batteries. Make an off-site data backup if it does not already exist.
72 hours before the storm: Coordinate with programming to have backup programs available in the event that the satellite dish is damaged, the internet goes down, etc. Inventory and restock PPE, emergency food, water, blankets, first aid supplies, batteries, etc.
48 hours before the storm: Procure supplies needed to secure buildings and sites (plywood, tarps, sandbags, rope, nails, screws, etc). Work out backups for internet STL systems if possible. Work on access plans to remote sites. Make sure that you have the proper tools available.
24 hours before the storm: Secure your personal dwelling, and make sure you have a plan for pets and loved ones. Secure proper shelter for everyone. Fill vehicle gas tanks, and fill portable gas tanks. Update off-site data backup and secure in a safe location.
12 hours before the storm: Secure buildings, park vehicles in areas where they will not be damaged by flooding or blowing debris, and make any last-minute supply runs for emergency food and water. Have a set or two of dry clothes and shoes in your vehicle (almost nothing is worse than spending 12-24 hours in wet and cold clothes). Coordinate response with other station personnel, prioritize the order of restoration, and coordinate with local authorities on their needs.
A few years ago, I purchased one of these LiPo battery chain saws:
These are great units because you do not have to carry cans of 2-cycle gas around. This model will cut trees 12-14 inches in diameter and I get about 25-35 minutes of cutting time per battery depending on the motor load. I have used it several times to cut small trees from access roads to tower sites.
Above all else, during and after the storm, be safe. Do not take any risks involving downed wires, damaged towers, satellite dishes, etc.
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.
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.
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.
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.