A Practical Guide To RF In Broadcast: Other Radios In TV Stations

Why keeping control of wi-fi and other devices within a broadcast facility to ensure there is no interference with critical devices is essential.

During the first half of broadcast TV history there were only five sources of program and commercial content: Live in-studio, live broadcast microwave, film, videotape, or a national network via ATT telephone (telco) lines that needed an on-site daily ATT telco crew to equalize as telco network performance changed. Early video-capable satellites were only affordable for world-class, live rock concerts. Syndicated film and videotape programs were shipped overnight. Walkie talkies were the only portable communication.

Fast forward to the post-analog, digital nirvana era. Videotape and film are expensive and virtually obsolete. Nearly everything historically important has been digitally archived. Everybody has a cellphone, high-speed internet access, and more than a few know how to live stream to social media. Most TV content is transported digitally and much of that activity is wireless, as is nearly everything else in the world today.

Q: How many wireless devices are within your reach right now? Which might be transmitting? RF management in a facility built on RF has become as mission critical as transmitting the broadcast TV signal itself. Interference is unacceptable.

In the ‘80s the TV industry widely adopted infrared controls which were somewhat compatible within each manufacturers’ standards. Compatibility between different models can be iffy, but the problem with IR display remotes is when you want to control only one of several similar models on a video wall or control room from a distance. Radio remote controls are targeted so don’t have the same problem.

Radio (RF) does not require line-of-sight between the transmitter and receiver as infrared does, and transmitters are usually matched to receivers. Uses for radio remote control can be handy and sophisticated, ranging from electric garage door or gate openers, automatic barrier systems, and burglar alarms to Wi-Fi, Bluetooth, cellphones, and smartphones. Typical RF remote control standards are Bluetooth with Audio/Video Remote Control Profile (AVRCP), Zigbee (based on IEEE 802.15.4), or Z-Wave mesh networks. Modern garage door opener transmitters operate on 310, 315 and 390 MHz. Older garage openers can transmit between 300-400 MHz. Modern car key fob remote frequencies are 315 MHz in the USA, and 433.92 MHz in Europe. Nearly all car key fobs operate somewhere within 275 to 450 MHz. Roku remotes use 2.4 GHz Wi-Fi. Rogue RF signals from myriad sources can be on nearly any frequency. Receiver beware!

One Way To Two?

Traditionally, broadcasters have always communicated with their audience in a single direction. Audience feedback was by mail, phone calls, letters to the local newspaper, and services such as Nielsen ratings. Stations transmit on their licensed broadcast channel and often use private broadcast auxiliary service (BAS) channels for studio-transmitter links (STL) and remote studio links. Most early remote-control technology for links was by dual-tone multi-frequency (DTMF) touch-tones on a dial-up telephone line or a dedicated 2-way system. Some systems counted pulses from a rotary dial for commands. It was crude but broadcast engineers made available technology work.

The first, battery-operated, low-frequency, wireless, consumer electronics, remote control radio transmitter was the 1939 Philco Mys-tery Control.  Pulse-count modulation (note the rotary dial) made it the first digital wireless remote control.

The first, battery-operated, low-frequency, wireless, consumer electronics, remote control radio transmitter was the 1939 Philco Mys-tery Control. Pulse-count modulation (note the rotary dial) made it the first digital wireless remote control.

In the late 2000s, the internet became fast, simple, and ubiquitous as did iPhones and Androids, and by design they could all connect wirelessly to all kinds of broadcast gear by a GUI via cellular digital data or local Wi-Fi. The smartphone became the new engineering tweaking tool, more powerful and repeatable than screwdriver adjustments.

In a typical, brick and mortar TV facility, digital IP data over RF remains easy to manage thanks to static IP addresses. If all wireless gear in a station uses static IP addresses, a rogue cell phone entering the building with Dynamic IP turned on shouldn’t interfere with network devices, right? That is, until one of the static devices in the facility happens to be offline for one reason or another.

That situation caused a couple of hours of grief during a production I was engineering when one device was temporarily unplugged during setup and a part time crew member walked in the studio with a phone set to DHCP that knew our usual Wi-Fi login. It logged onto the temporarily unused static device address our TV gear was assigned. When we plugged our static IP TV gear back in, it was blocked due to the address conflict.

In the field, such as in OB or live news events where gear may need to be reconfigured for specific circumstances and events, IP addresses can change and more rogue cellphones scanning for Wi-Fi networks to log onto may wonder into range. Often the problem can be a phone set to dynamic IP carried by a part-time crew member who has logged onto the OB or newsroom Wi-Fi system before. Any production system IP address beginning with 192.168.x.x is asking for trouble.

Of course, the most significant change to consumer TV consumption is streaming video and the internet. ATSC 3.0 is designed to take advantage of all this with IP protocol and two-way communication between TV stations, viewers, and others. ATSC 3.0, aka NextGenTV, will be the topic of the next chapter.

Spectrum Analyzers

Spectrum management is a complicated issue at world-championship events. Every broadcast device that transmits radio waves, such as a wireless mic or video transmitter, must be registered and its antenna physically tagged before it is allowed into the stadium. Local broadcast groups such as the Society of Broadcast Engineers (SBE) use local frequency coordinators to help oversee and manage the concentrated deluge of RF transmissions in such a tight space. The primary electronic tool used before and during the broadcast to monitor the RF spectrum in a world-championship stadium are RF signal analyzers with directional antennas.

When not analyzing ATSC 1.0 Shoulder Attenuation, a spectrum analyzer can be a useful RF security monitor.

When not analyzing ATSC 1.0 Shoulder Attenuation, a spectrum analyzer can be a useful RF security monitor.

Benchtop and handheld spectrum analyzers are as popular as they are different in frequency ranges, analysis bandwidths, and displayed average noise levels (DANL). Some spectrum analyzers are specifically designed to be ‘broadcast analyzers.’ They receive and analyze a particular FM or TV signal, a video and MPEG TS, and also function as a general-purpose spectrum analyzer, all in one device.

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