How Helical Antennas Make a Safer Set
Beefing Up Audio and Video on Renny Harlin's 12 Rounds
Watching the Super Bowl with audio on his mind, Ledford noticed some funny-looking antennas in use. Inspired to research the special properties of those helical antennas – often used for sports telecasts, TV award shows, and studio broadcasts but not so much in feature films – he decided to track down the company that provided them to the Super Bowl and ended up in contact with Carl Cordes, general manager of Professional Wireless Systems in Orlando, FL.
One big advantage of the helical design has to do with polarization, says Cordes. “A whip antenna or a directional antenna is linear-polarized,” he says. “The pick-up pattern is generated in a linear or horizontal plane. With the helical, it’s actually a circular pattern. It’s kind of like you’ve got a ball of energy instead of just a line of energy. When you’re trying to transmit to or pick up from a linear, you have a greater chance of success, because now you’re dealing with a 360-degree pattern instead of just a line across a compass face.”
That sounded good to Ledford, who promptly rented a helical kit from Professional Wireless for testing purposes. He drove around commercial and downtown districts to test the system’s capabilities and says the results were “amazing.” He purchased a kit with two helicals and two shark-fin antennas, and eventually purchased a second kit to handle some of his other RF needs.
The results were exceptional on 12 Rounds because the transmitting vehicle and the receiving vehicle were both moving, meaning the helical antenna’s circular pattern helped maintain the signal even when two weren’t in the same plane. “Cars take a corner, and if you have body packs on the actors, they may go flying through the air horizontally,” he says. “With more traditional antennas, if you have your antenna and receiver both in the vertical plane, everything’s hunky-dory. But that wouldn’t be guaranteed in this kind of show.
“The helical antennas improved our range tremendously, and that was a big help. Not only did we get good, solid dialogue out of the car and a good RF signal, but it also gave us range, so the chase van we constructed did not have to be right on top of the action. There were a multitude of vehicles flying down the street, and we could work back farther, at a safer distance, which the stunt people enjoyed.”
How much farther? It depended on circumstances. “We would always feel very good about two blocks,” Ledford recalls. “Sometimes we could go further. We did a whole streetcar sequence, and when the streetcar went back to its original position that would be five or six blocks, and we could get clear, no-hit audio and there were other shoots working in town. A lot of that has to do with getting the antennas out of the metal shell of the vehicle. We’d use these little external antennas that you can screw into the transmitters. Because the helical can work in any plane, oftentimes we would have the antennas off to the side of the car, away from camera.”
“It depends on a variety of things,” Cordes agrees. “If you had two helicals in fixed positions you could go quite a distance. Over water it goes farther. Typically, you’re going to get about twice the distance from helical compared to other directional types of antennas. For people who are only using the standard whip antenna, you’re probably at four times the distance [with a helical design].”
Even video-assist operator Chris Murphy became a believer, buying a kit when he figured out helical would extend the range for video as well as audio. “It’s wireless transmission regardless, and much better performance than what we were using,” Murphy says. Murphy liked the gear so much he became a dealer, providing the antennas through his North Wales, PA, company, Video Village.