The Modulation Sciences DSPversity receiver
KWTV's news helicopter operations have won numerous local and national awards, and are especially in demand in this part of the world for applications beyond routine news coverage. Our television station also has a special responsibility in providing vital tornado information and coverage for our viewers. (We're located in the part of the country referred to as "tornado alley.") This responsibilitiy involves locating and following tornados to provide precise storm tracking information not available through other sources.
ATSC AND MOVING HELICOPTORS DON'T MIX
Reliable reception of ATSC television signals in a fast moving helicopter is really a big challenge. Actually, this is the reason that the new mobile handheld standard (ATSC A/153) was developed. However, the new standard for mobile DTV doesn't really provide a solution for the problems of modern helicopter television news operations. The long latency associated with 8-VSB transmissions and the lack of an IFB channel make attempts to use off-air station feeds in breaking news operations impractical in helicopter operations.
We had heard about Modulation Sciences' successful deployment of its IFB-over-ATSC product, the Digital Proceiver, and decided to contact them. The company responded with a prototype of its DSPversity IFB and ATSC diversity receiver, a four-channel diversity receiver with IFB and main channel ATSC picture and sound outputs. Modulation Sciences also offered to demonstrate their proprietary diversity antenna system for us.
Modulation Sciences visited us last summer and installed the DSPversity and its antennas on our Bell 407 helicopter in just a few hours. We spent several hours the next day in test flying the system.
The results were very impressive.
Our previous attempts at ATSC reception in the helicopter had not been sufficiently reliable to meet operational news needs, but the DSPversity did provide the reliability we needed. The test flight included the coverage of a simulated story. Reception was 100 percent solid for all segments of the simulation.
The receiver locked-in at a few hundred feet above ground and remained solid while flying to the "story" location, while orbiting that location and during the return to our base of operations.
REALLY SOLID RECEPTION
We then made an effort to determine the limits of performance. First we flew a series of "figure-eights." To our surprise, there was no null zone off the tail. Eric Small, the chief technical officer at MSI, was flying along with us and agreed that a null off the tail was common in both analog and digital helicopter IFB operations with UHF stations. However, because KWTV operates on a VHF channel, and the helicopter is small in terms of our Channel 9 wavelength, this tail shadowing was not really a problem in our case.
High-speed trials were conducted at about 140 mph, with runs both to and from the transmitter. These also failed to cause the system to lose lock. Actually, the only way we got the receiver to unlock was when the pilot jogged the aircraft along the line of flight at high speed.
We're now convinced that MSI has solved the problem of reliable ATSC reception in our helicopter.
Greg Ward is the news operations manager at Oklahoma City's KWTV. He may be contacted at firstname.lastname@example.org
For additional information, contact Modulation Sciences Inc. at 800-826-2603 or visit www.modsci.com