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The chief transmitter operator is responsible for keeping the primary transmitter(s) on the air, no excuses. Achieving that goal requires back up plans and redundancy ready. Sometimes redundancy can be a retired transmitter and/or antenna, a second AC power feed and/or substation from the local power provider, or a separate backup AC power feed from a local generator. It all depends on what station owners consider a reasonable risk and what they are willing to invest in technical insurance.

When I was the Assistant CE at KCTV, every year the CE made a Capital Expenditure (CapEx) request for an expensive back-up generator system with automatic change-over switching. Corporate management always responded: Your average off-air time due to power failures is about 5 minutes per year. That’s an annual loss of 0.0000095% of total airtime, and a risk we are willing to take.

When I became CE and my similar CapEx requests were similarly turned down, my response was always that the big one will happen during the Super Bowl or equivalent huge broadcast moment, guaranteed. Corporate management always harrumphed, excused themselves, and flew back to corporate HQ.

Major TV technical meltdowns rarely occur overnight when nobody is watching, and the ad revenue barely covers the station power bill. The ultimate rule is “The larger the TV event and audience, the more inevitable an embarrassing technical failure will occur at the worst moment possible.”  TV karma ensures the drama.

Hello Reality

The Kansas City market ultimately experienced its worst ice storm in recent history, and my TV station lost studio power from our primary and secondary feeds for several prime-time hours. Fortunately, the transmitter was in a separate downtown location that never lost power.

We barely kept the station on the air with several ENG van generators and extension cords powering key Master Control racks, while the news department was doing news and weather in a hallway with whiteboards and typewriters because there wasn’t enough power for the newsroom or weather computer systems or studio lights. We met our primary goal to keep the transmitter, STL and network feed on the air. Producing news and weather in the hallway was a bonus. The crew made it happen and it was fun.

At the next CapEX meeting, I presented fresh generator proposals, and station owners couldn’t wait to invest in a serious diesel generator system at the studio with days local fuel storage. Of course, the inside joke was that most local cable systems were down and most of the few who had power couldn’t have seen us anyway. However, staying on the air during a major ice storm disaster made for some classic station promos and war stories.

Remote Probe Solutions

Remote probes are easy to deploy and only need AC power and an internet connection. They are ideal to remotely verify signal strength and quality at problematic receive locations. Nearly every TV station has a few null zones behind some buildings and hills and most chief engineers/operators know exactly where they are from viewer complaints.

A variety of RF probes are available to remotely monitor ATSC 1, ATSC 3, ISDB-T and DVB-T2 RF signals. Some use software-defined radio (SDR) technology, others are dedicated systems or USB sticks that run on a PC. Most can capture, analyze and report full stream and advanced RF properties such as RF level, demodulation status, modulation error ratio (MER), bit error rate (BER) and transport stream performance. Some probes can monitor IPTV multicasts and a range of RF formats including DVB-T/T2, DVB-S/S2/S2X, DVB-C, QAM-B, ATSC1.0, ATSC3.0, ISDB-T and ASI.

My experience is that a new transmitting antenna with different beam-tilt and polarization replaces most known null zones with unpredictable new ones. A better answer is a SFN transmitter or two to fill in gaps. That, and monitoring null zone reception with remote probes makes for fewer viewer complaints and are much easier to deal with.

The Break Room Reference

In the analog days, no RF signal resulted in an annoyingly obvious hiss from the TV set speaker. DTVs without a signal go black with no sound. If you aren’t paying attention, you may not notice a problem.

Many TV stations use TV sets with built-in antennas tuned to the station’s on-air signal 24/7 in the lunch/break room and the station lobby. If the station goes off-air, someone getting coffee at the station will notice. Cable systems aren’t necessarily reliable because many get station signals by fiber from the studio, not OTA.

Many of the most loyal local OTA TV viewers are cable-cutters, watching cheap TVs with inferior antennas. A cheap DTV set using a paper clip antenna is one of the most unforgiving and least expensive test set-ups available to verify and evaluate real-world OTA TV performance. Expensive professional TV demodulators with outdoor antennas can mask some subtle issues that commodity TV tuners can’t handle. Who wants to watch signals with digital artifacts?

The more people that can easily view your signal, the more likely they are to watch. Poor analog signals were annoying but viewable if you wanted to watch. Poor digital signals are blocky, jerky at best, and generally frustrating or impossible to watch. Squinting through the snow is no longer an option. Digital either works perfectly or viewers change channels.

SFNs Are The Future

Another application for remote probes is single frequency networks (SFNs). SFNs are a major element in the ATSC 3.0 rollout for data and TV. ATSC 3.0 data may feed self-driving vehicles, which call for a useful, live, RF signal along rural highways. Delay can create danger. Following the cellular model, more localized transmitters and antennas on shorter towers have proven to be the best way to reliably communicate with devices in moving vehicles with minimal latency.

Self-driving vehicles will increase the demand for simultaneous real-time road data to be fed to many vehicles. Right now, most vehicular digital communication is one-to-one cellular data to and from vehicles. Someone pays for that data, byte-by-byte, vehicle by vehicle, and it’s not simultaneous. SFNs resolve that issue.

ATSC 3.0 SFNs are easier to manage. ATSC 1.0 requires a delay set at the exciter to sync one transmitter to the next on the same channel. The ATSC 1.0 delay creates sweet spots and nulls between the transmitters that move around as the delay is adjusted, making the dream of blanket SFN coverage of all locations between transmitters impossible. On the other hand, it is easier to focus the ATSC 1.0 signal on towns instead of pastures.

ATSC 3.0 receivers process competing signals on the same channel entirely differently, resulting in more reliable reception with significantly fewer null zones.

SFNs are unique opportunities for broadcasters that can be resolved with multiple-tower, lower-power transmitters operating on the same SFN channel along rural interstate highways. Several TV transmitter manufacturers make outdoor, tower-mounted transmitters that are incredibly small and easy to install and operate. SFN transmitters can be daisy-chained to connect to the studio via an ATSC receiver tuned to a nearby SFN transmitter, or via STL or satellite. If you can control and monitor multiple transmitters operating on the same channel from a remote location via the internet, you have achieved SFN.

SFN Realities

I was chief transmitter operator at a five-transmitter SFN in Springfield MO, Fox affiliate KRBK-TV. It was a full power station, running between 1-5KW TPO at transmitter sites. Four of the five SFN transmitters were spread across rural pastures throughout the DMA, as close as possible to the nearest rural town. The fifth transmitter was in the city of Springfield. Internet service and bandwidth at the rural transmitter sites was quite limited, and there was no clean RF path from the studio to any of the sites for a single microwave STL.

Daisy chaining from transmitter to transmitter would be the easy way but would introduce too much delay to dial in the correct delay at each transmitter exciter, with tower-to-tower receive antennas mounted high on the towers. The least delay would be at the end of the chain, and delay at the other transmitters would have to be more than the one at the end for the timing of all the transmitter signals to match. The exciters didn’t allow that much delay adjustment.

A satellite STL was the only realistic option to feed all five transmitters simultaneously for the SFN to work. A half-transponder on a digital satellite 24/7/365 cost the station about $30K US monthly, or about $6K USD monthly per transmitter.

It wasn’t cheap, but the economic, signal timing, reliability and the fact that each transmitter site would need a tall antenna, a professional demodulator and a video to ASI converter to feed the exciter. It made a satellite STL with ASI output for the SFN transmitters the most practical option.

A problem in the Springfield MO market that we soon realized was that viewers pointed their outdoor TV antennas at the Springfield MO antenna farm in Fordland MO (1604’ base elevation), where all the major stations were. KRBK didn’t have a transmitter at or near that location. Lots of viewers couldn’t see our SFN channel because their antennas were pointed the wrong direction. The KRBK SFN remained in service until the station was purchased during repack and moved to a shared 2000’ tower in Fordland MO.

ERP Tip

Did you know the FCC only counts the ERP of the horizontally polarized signal in ATSC transmission so long as the vertical ERP component doesn’t exceed the horizontal ERP.

FCC 47 CFR 73.662 Transmission Standards about ATSC transmission states: “(14) It shall be standard to employ horizontal polarization. However, circular or elliptical polarization may be employed if desired, in which case clockwise (right hand) rotation, as defined in the IEEE Standard Definition 42A65–3E2, and transmission of the horizontal and vertical components in time and space quadrature shall be used. For either omnidirectional or directional antennas the licensed effective radiated power of the vertically polarized component may not exceed the licensed effective radiated power of the horizontally polarized component.

For directional antennas, the maximum effective radiated power of the vertically polarized component shall not exceed the maximum effective radiated power of the horizontally polarized component in any specified horizontal or vertical direction.”