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Transmitters are magic that few but RF design engineers, broadcast engineers and serious amateur radio operators understand. Once a transmitter is tuned to its companion fixed frequency antenna, the only thing to do to prevent failures is to watch for trouble before it happens such as dirty air filters, questionable visible anomalies, feedline issues and transmitter readings by exception.

Quality of Service (QoS) is an objective system that typically measures bandwidth, delay, packet loss and jitter. Quality of Experience (QoE) subjectively considers factors influenced by humans, electronic systems, and context.  Most QoE is focused on subjective QoS measurements and often uses a mean option score (MOS) to assess the objective quality of the media with algorithms.

The QoS and QoE of a TV signal starts at the sources of TV systems backhauling live TV content, often at less than one watt and often on public Wi-Fi into the station router. There’s much more to high TV QoS and QoE numbers than maintaining authorized TV transmitter TPO and ERP. Trouble usually begins at or near a field source.

Keep CALM & Carry On

If you ask viewers what annoys them most when watching TV, many will complain most about loud commercials. All a viewer needs to do to file a CALM Act complaint with the FCC is to provide specific information about the station or MVPD channel, TV program name, date and time of the occurrence and the sponsor(s) of commercials that seem louder than the programming they accompany. If the FCC sees a pattern or trend, it will likely be investigated.

The equivalent in Europe is EBU R128 which forms the basis of mandatory requirements in individual countries. Many other countries globally, reference ITU BS.1770-5 for their individual mandatory requirements. In both instances there are broad similarities to the CALM Act.

Most Master Control operators I ever worked with complained about highly compressed, loud commercials too. I have the tinnitus to prove it.

To this day, most viewers still complain that many commercials are too loud.

The best part about the Commercial Advertisement Loudness Mitigation Act (CALM Act) is the requirement that TV commercials have the same average volume as the programs they accompany. CALM Act went into effect in December 2012, and it requires stations, cable operators, satellite TV providers and other multichannel video program distributors (MVPDs) apply ATSC Recommended Practice A/85 to commercials.

The second-best part is that CALM Act data is that it is simple to monitor and document loudness with the right test gear. Unfortunately, not all cable channels or video streams seem to abide by the CALM Act.

ATSC A/85

A fixed or agile normal dialog level (dialnorm) is established by ATSC A/85. A fixed dialnorm value poses minimal content risk with no metadata requirement. An agile dialnorm allows setting different dialnorm values for different content that has different loudness. This is accomplished by embedding the dialnorm parameter within the metadata bit stream accompanying the content at an upstream location. The metadata is dis-embedded just prior to the AC-3 encoder and connected to its external serial metadata input.

Dialog level (dialnorm) is what makes the CALM Act an objective measurement that must be set correctly to prevent potentially severe loudness variation during content transitions on a channel and when changing channels across the DTV dial. Dialnorm values may be set from 31 to 1. An incorrect dialnorm value setting can cause a loudness variation as great as 30 dB.

The CALM Act calls for maintaining a target level of -24 LKFS. The acronym LKFS stands for “Loudness, K-weighted, relative to nominal Full-Scale.” LKFS represents the amplitude level that is communicated to the viewing audience in decibels (dB), but it focuses on the audio elements that viewers recognize the most. LKFS is significant because it provides an integrated measurement over time.

Achieving the minus 24 LKFS target level often requires increasing high frequencies and dropping lower frequencies across all 5.1 channels, with additional calculations around power averages for each audio file. If all content sources universally used the ‘dialnorm’ standard, dialog levels would be consistent and uniform from channel to channel. Interestingly, the CALM act only applies to TV commercials, not program content.

Many T&M products will log, measure, and display LKFS values. Some CALM Act monitoring gear includes aircheck auto-logging that reproduces technically accurate audio levels and can be used to prove LKFS values. Accurate CALM Act logging and archiving is the best possible protection from ‘loud commerical’ complaints and FCC loudness investigations.

STL/TSL Options

Many full-power TV transmitters are in remote locations on mountains or pastures, most with less than reliable inexpensive high-speed internet service. The traditional method of linking a studio to an off-site transmitter was with a broadcast auxiliary service (BAS) link primarily on 2GHz, operating on seven, 12 MHz wide protected bands from 2025.5 to 2109.5 MHz. A broadcast license is required for FCC permission to use BAS frequencies.

The problem with BAS is that it is a one-way simplex system. Typically, the transmitter/studio backhaul link was a dedicated POTS (plain old telephone service) line to send low-bandwidth telemetry data to the studio for live monitoring and logging.

Most DTV transmitter exciters require an Asynchronous Serial Interface (ASI) to carry a multi-channel MPEG Transport Stream (MPEG-TS) by fiber, copper or RF from the studio to the transmitter. The only purpose of ASI is to transport MPEG-TS to a TV transmitter broadcasting an ATSC or DVB-T transport stream. ASI can be delivered over IP because MPEG-TS is the lowest common denominator of all long-distance broadcast media transport.

The ASI standard is part of European DVB and maintained by the European Committee for Electrotechnical Standardization (CENELEC). ASI carries serial MPEG-TS data with a constant maximum bit rate of 270 Mb/s.

Only Bits

An STL link can use fiber, professional Wi-Fi gear, a private wired network, cellular data or a satellite to link the multi-channel, ASI stream from the studio to the transmitter. It all depends on the reliability of high-speed internet access at the locations of the studio and transmitter(s).

Sometimes, line-of-sight RF is impossible or impractical, and there is no fiber near the transmitter site. When the best communications connection at your transmitter is a copper POTS line miles from the TELCO exchange building, your only reliable video transport option is a satellite STL, usually a half-transponder. Fortunately, most satellite receivers have an ASI output that connects directly to most TV transmitter exciter inputs. Unfortunately, satellite time is expensive but there may be no other viable options.

Currently, the new digital STLs are duplex and include TSLs. If you are fortunate enough to have a reliable high-speed or fiber internet connection at your transmitter site, you can use a digital STL/TSL for full duplex backhaul of audio and video with telemetrics back to the studio. Duplex communication makes transmitter remote control significantly easier.

ATSC STLTP

ATSC STLTP makes digital STL/TSL links possible and compatible. The ATSC 3.0 Studio-to-Transmitter Link Transport protocol (STLTP) was defined by ATSC A/324 in 2018 and upgraded several times since. A/324 is a Security Layer to protect TV stations from person-in-the-middle hack attacks to content delivery. It defines delivery protocols for ATSC 3.0 Link Layer Protocol (ALP) Transport.

A/324 also defines possible interfaces among the studio infrastructure, for example the interconnection of the ALP and a Broadcast Gateway. It also specifies certain constraints on the scheduling of content and signaling on the Physical Layer. The described scheduling process enables Preamble generation and emission time management. It specifies certain aspects of transmitter behavior and certain parameters of transmitter operation.