Another Low Power TV installation

One of the many projects we are currently finishing up. Over-The-Air TV is making a comeback.

A few things about LPTV; These stations usually have an ERP of 15 KW or less, and they are a secondary service, like FM translators, which a full-power TV station can displace.

Alive Telecom ATC-BCE48BB-V3-31 UHF slot antenna

This is an ATT microwave site built in 1977 according to county records. This may have been one of those VHF Mobile Telephone sites which existed before cellular telephone systems. ATT owned it until 2022 when it was sold to a private business.

This station is on channel 31 or 575 MHz center frequency. UHF TV stations often use slot antennas, which have gobs of gain. Slot antennas are simple designs that have a broad bandwidth and until recently were mostly horizontally polarized. This particular antenna is elliptically polarized which is becoming more common as TV providers are looking at mobile video applications.

WZPK 20 MHz VSWR sweep
WZPK 20 MHz return loss
Example of UHF slot antenna with Radome cover removed

Slot antennas are the inverse of a dipole antenna. A dipole is two conductive poles approximately 1/2 wavelength surrounded by free space whereas a slot antenna is 1/2 wavelength of free space surrounded by a conductive plane. The width of the slot determines the bandwidth of the antenna. Radiation from a dipole is in the plane of the two poles versus the radiation from a slot that is perpendicular to the slot. At UHF frequencies, many slots are placed on the radiating plane, giving large gain figures.

Transmitter rack with 6-pole Comtech mask filter

All TV transmitters require a bandpass or mask filter. This is to keep out-of-band emissions out of the tightly packed TV spectrum.

S11 return loss, looking at the antenna through the mask filter
Post-mask filter channel bandwidth

These filters need to attenuate the upper and lower shoulders of the digital carrier by 46dB +/- 3.25 MHz from the center frequency.

Comtech 6 pole UHF TV mask filter

These are fairly straightforward filters, this one has six cavities with plungers that slide in and out to adjust the tuning. I watched one of these get retuned in the field, it takes quite a bit of time and patience to complete and requires a two-port network analyzer.

400-watt UHF amplifier, exciter, and IT gear; WZPK-LD

With the TPO of 400 watts, the ERP is 4.7 KW horizontal and 2.35 KW vertical.

Longley Rice coverage map; green is easy indoor, yellow is outdoor, red is difficult outdoor antenna

So, why bother with all of this? Indeed that is a good question. As cable companies continue to raise their rates (the average cable TV bill is $250 or so) people are looking for alternatives. Cord cutting is a thing and OTA (over-the-air) TV as well as OTT (over-the-top or direct streaming) are popular alternatives.

UHF “Bow Tie” consumer TV antenna

This station will run France 24 English service and NASA TV to start. Other things you can find on Low Power TV stations; Heartland (mostly country music with some cooking shows mixed in), Retro (old movies), Rewind TV (Old TV shows), Buzzr (old game shows), Court TV, Weather Nation, News Net, etc. More information on OTA TV networks can be found here:

Rabbit Ears has a good signal search page if you are interested in OTA TV:

More information on Low Power TV (or Local Power TV) and be found here:

For a sometimes interesting discussion on cord cutting in general, try this:

Some More TV work

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 parts
3 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.

WKTV RF channel 29, 708 KW ERP, 990 foot (302M) tower

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.

TV sweeps

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. 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 top
Selfie; 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.

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
Dielectric 8 pole channel mask filter
WMED 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, Maine
WMEM-DT test load and coax switch
WMEM 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.