DTV Update
KFMB-DT Finally Ready for Prime-time
By Gary Stigall, CSTE
Chairman, Chapter 36
KFMB-DT, UHF 55, seems to up for good now, blessed by the wizards from the Comark east coast factory.
Rick Bosscher, station RF supervisor, said they finally traced a problem with the Advantage transmitter occupied bandwidth instability to a missing sheet of ferrite-impregnated material in one of the drivers. Some questionable connector shields were found in the course of troubleshooting as well.
The system has been transmitting full-time since Thursday, February 24.
KFMB-DT transmits high-definition on its primary channel, upconverting daytime, and passing CBS HDTV material as available. CBS currently averages ten hours of high definition programming per week.
Ye Olde NTSC Beast Reeks Havoc
as Though a Lonely Dog in a House Full of New Furniture...
Rick has learned that having the old transmitter dump during the first minutes of the Buick Invitational Golf Tournament helps sell the notion of buying a replacement.
One of two parallel transmitters of the 28-year-old RCA TT-50 suffered two unrelated interlock failures Saturday afternoon, February 19. Rick called from home to reset the failed unit. Instead of a reset, the power-up sequence set off a main breaker overload, dumping the entire NTSC RF plant at the beginning of the semi-final round of the local golf classic featuring Tiger Woods going for a superhuman sweep.
What he found after an ambulance ride to the top of Mt. Soledad was not pretty. "Bran flakes," he remarked of the remnants of one visual PA tube. The transmitter had all but gone up in flames, the three cavities having overheated after a power phase sensing relay had shut off the blowers without a corresponding shutdown of the finals.
One transmitter came up after restoring the breaker. After 21 hours to rebuild two of the three cavities and conduct other repairs, the station was back up to nearly full power. The failures cost over $30-thousand to fix.
KFMB-TV has since ordered a Harris solid-state Platinum-series 45 kW channel eight transmitter, the last in town to upgrade.
Rick Bosscher first worked on the KFMB-TV transmitter pair installing field mods for RCA Field Service in 1974 after its 1972 installation. He was hired a few years thereafter to care for all the station's local RF properties. To say that Rick understands the strengths and foibles of that TT-50FH transmitter would be an understatement. He's been able to manage cavity maintenance in such a way that the PA tetrodes sometimes lasted more than 85,000 hours--three to four times average life for comparable systems. On the original RCA exciter, he knew the pre-distortion consequences of every adjustment.
Now the transmitter and peripherals is listed FOR SALE with Broadcast.Net and others.
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