Broadcasting employs the latest technology in many areas, but controlling the broadcast hardware connected to the antenna and the related transmission power, source, and facilities is usually still a low-tech operation. Typically, a broadcast engineer will drive to the unattended transmitter, translator, or repeater site to flip switches and make other manual adjustments (Figure 1).
In radio and TV broadcasting, it’s important to focus on the transmission system because this is where all of the hard work in the studio is disseminated to listeners. iHeartMedia, which oversees ten radio stations in the Los Angeles metro area, has automated the switching and backup functions of its antenna and transmitter system using programmable logic controllers (PLCs). As a result, they have improved operations, cut costs, and increased reliability. In addition to radio stations, iHeartMedia owns outdoor advertising, and also has a large online radio presence in the form of the iHeartRADIO app.
Controlling the audio, antenna, and transmitter in a broadcasting system used to be a manual process. In more recent times, broadcast-specific remote control systems have been deployed to provide rudimentary control via dialup modem. With these systems, alarms can be set up to notify personnel by phone or email if there is an issue. The systems can also have macros programmed to handle automatic functions. However, the cost, reliability, and simplicity of these systems don’t come close to what the PLC can deliver.
Interfacing and Control with PLCs
Although using PLCs to control transmitter functions is unfamiliar to many broadcast engineers, the hardware commonly used in industrial automation works well for control and monitoring of transmission facilities. A 50,000-Watt transmitter site consumes about 150 kW of power and contains air conditioning, power distribution, and backup power systems.
Over the years, broadcast engineers have upgraded manual monitoring of transmission facilities by applying custom electrical cabinets filled with relays, timers, diodes, and capacitors. Some are even taking a Raspberry Pi and interfacing it to a motor or blower fan using contactors and relays, which is not the simplest, most cost-effective, or the most robust design. By contrast, a PLC is designed to reliably control contactors, relays, and other components in an industrial setting.
Many broadcast engineers spend a lot of time developing interfaces among different components and items of audio equipment. They then figure out a way to integrate it all into a system, but the control hardware they use is often not suited to the task.
Automating Broadcast Functions
Automatic failure switchover and remote access are sorely needed in broadcast because many of the remote transmitter sites aren’t readily accessible, particularly during periods of inclement weather. The discrete manufacturing and process control industries have been automating with PLCs for years to provide remote access and other advanced functionality, and iHeartMedia is now adapting this technology to broadcasting.
One application is at iHeartMedia’s Dodgers Flagship station, KLAC AM 570 in Los Angeles. This system uses the AutomationDirect Productivity2000 controller as an antenna/transmitter controller for a number of reasons (Figure 2). KLAC’s antenna/transmitter controller had to include email notifications any time the system did a transmitter pattern change or an error occurred, which is a built-in function of the Productivity2000 PLC. It also has a built-in proportional-integral-derivative (PID) loop, which will be needed for building environmental control when added in a future project.
KLAC is a directional, amplitude-modulated (AM) radio station. In the daytime, it operates using a single tower (antenna) in non-directional mode. At night, it uses two towers to produce a more directional signal to avoid interference with other stations on the same frequency, which is needed because AM signals travel farther at night.
The PLC automates the switching between daytime and nighttime patterns. Using the real-time clock in the controller, iHeartMedia designers built a table to control the switching time in compliance with FCC regulations. The PLC performs the automated pattern change and sends an email to confirm.
The Productivity2000 PLC and an AutomationDirect C-more touch panel display are the main components of the automation system that’s also used to control and monitor the status of the station’s main and backup transmitters. When broadcasting a Dodgers game, the station absolutely has to be on the air, and the reliability of the PLC ensures a continuous transmission signal.
The PLC monitors the status of the main transmitter and will try to restart it if it fails. If unsuccessful, it automatically switches to the backup transmitter. If the backup fails, it switches to a third-level transmitter and lowers power if necessary to keep at least a weak signal on the air.
The automation system duplicates what a human would do at the site, automatically handling antenna switching, pattern change, parameter monitoring, and other functions. It also performs datalogging per FCC guidelines, with this information available remotely. The PLC has a built-in Web server, so logged data can be accessed remotely via any browser. In this case, it is done through a Cisco firewall at the site.
PLCs have been very reliable compared to the custom control systems used previously. The PLC controls a wide variety of off-the-shelf audio switchers made by various companies. For the radio antenna switching, the PLC is controlling large RF contactors. These devices are controlled by mixing and matching the PLC’s input and output modules including discrete, analog, relay contact, and serial I/O. Using these I/O points, the PLC can be interfaced to all of iHeartMedia’s broadcast equipment.
A C-more touch panel display was installed and used to create a main screen with buttons to change modes of operation or select a transmitter (Figure 3). The main screen also displays current time and transfer times for the month, along with a wide variety of analog parameters such as transmitter output, current to the antenna, and system status. And if needed, a calibration screen can be accessed to scale the analog values to actual engineering units.
Test, Installation, and Startup
Installation and startup of the antenna/transmitter automation system took significant planning to minimize impact on broadcasts. Several test jigs were built to verify operation of the automation system prior to installation, with simulated transmitters built to specifications to make the test as close to the actual installation as possible.
For testing, three simulated transmitters were plugged in and RF contactors were connected. The complete KLAC setup that the PLC would be controlling was simulated, and iHeartMedia performed weeks of testing. After some tweaking and optimizing of the PLC and C-more programs, the resulting automation system worked far better than anything that had been installed at KLAC.
The installation went as planned. There were more than 30 cables to install, and AutomationDirect ZIPLink modules were used to reduce wiring time. To reduce off-air time to the absolute minimum, signals were bypassed with jumpers until tested so the station could continue transmitting while the new automation system was installed.
There were a few minor tweaks required to the program during onsite startup. When switching transmitter patterns from day to night, the RF signal from the transmitter must be muted to avoid putting 50,000 Watts through a contactor and damaging it. Tweaking was required to minimize the time that the station was off the air when switching. Actuation times of contactors and RF power-off delay of transmitters needed to be fine-tuned, and when this was completed, the pattern switching was barely audible.
iHeartMedia plans to use PLCs to automate many more broadcast systems including automatic FM antenna switching, power control, and transmission line pressurization and fault detection.
This article was written by Dennis Sloatman, Vice President of Engineering and Information Technology at iHeartMedia, Los Angeles. For more information on the AutomationDirect equipment used in this application, visit http://info.hotims.com/65848-326.