I found a great resource for learning about test and measurement on Rohde Schwarz’s YouTube channel. Each video is about 5 to 15 minutes long and covers the basics of RF test equipment, measurement parameters, and definitions.
Measuring RF systems is an important part of Broadcast Engineering. Many folks think that RF plants are going away, replaced by all IP content distribution. I disagree; Terrestrial Broadcasting will be around for a while yet. AM and FM radios are still ubiquitous in cars, homes, businesses, etc. There is no other information distribution method that is as simple and robust as over-the-air broadcasts. That is why Federal Emergency Management is still spending money on hardening broadcast facilities.
The Internet and Mobile Data in particular are susceptible to failure in emergencies. Cellular networks were almost useless due to congestion or system outages during the 9/11 attack or a natural disaster such as Hurricane Sandy.
Radio still has a role to play.
As the older Broadcast Engineers retire, there is a dearth of qualified RF specialists who can make accurate measurements on antenna systems, filters, and other transmission system components. There are very few mentoring opportunities, especially in commercial broadcasting. Gone are the days of several engineers on staff, when there was time to teach the younger people some hard-learned lessons. One of the reasons I write this blog is to pass along some of that knowledge to others so that the industry might survive.
GatesAir contracted me to go to Utica, NY, and do some repair work. WKTV has a ULXTE-50 UHF transmitter which burned out an RF elbow between the UHF combiner in cabinet 1 and the UHF low pass filter for cabinet 1.
Burned-out RF parts3 Port UHF combiner, cover removed for cleaning
There was a bunch of burned debris in the bottom; little bits of melted metal and plastic.
Bottom of UHF combiner
We first vacuumed out as much stuff as we could get. Then used an air compressor to blow the rest out and wiped everything down with clean rags and Windex.
Once that was done, the unit was reassembled and reinstalled in the transmitter. A new elbow, UHF low pass filter, and direction coupler were installed and the transmitter powered back up.
The transmitter site is actually located north and slightly west of Little Falls, NY. The station has been on the air since 1949 and the original GE transmitter is still in the garage. It was difficult to squeeze in and get a look at the transmitter, however, the operator’s console was out in the open:
GE TV control operator’s console, circa 1949
In most places, this would have been thrown out years ago. Now, it is a museum piece. Lots of interesting history in the Wikipedia article, too.
We have been really busy this fall working on multiple projects plus the day-to-day tasks. One thing that is always fun; sweeping antennas with a VNA.
In this case, WVIT Hartford, CT needed to repair a leaking transmission line section just below the antenna. To ensure that there would be no problems with return to the air at full power, we did a before sweep and after sweep.
WVIT is the ATSC 3.0 lighthouse station for the Hartford Market. FCCinfo.com has the station listed as ATSC 3.0.
WVIT Tower, Hartford CT
The WVIT tower is 1,100 feet tall and is located on Rattlesnake Mountain near Farmington, CT. Most of the other Hartford TV stations are on the same hill.
Tower crew, hitching a ride to the topSelfie; return loss looks good
It is always interesting to see new places and meet new people. This site has an auxiliary TV studio, which they were using during COVID.
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, MaineDielectric 8 pole channel mask filterWMED transmitter site
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, MaineWMEM-DT test load and coax switchWMEM Transmitter site, 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.
WMEM S21 mask filter sweep
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:
Wind Turbine, Mars Hill, Maine
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.
