Quote:
Originally Posted by Piggie
This to me falls in the surprise surprise category.
Digital just doesn't work on Low Band VHF (Ch 2-6) because there so much noise on that band. Leaving it as a TV Band was a total joke and only used to justify grabbing 51-59 from TV broadcast.
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Disney/ABC should have learned from the experience that CBS-owned WBBM-TV/DT was having in Chicago before electing to move WPVI-DT to channel 6, the channel used by analog WPVI-TV. WBBM-DT was broadcasting on channel 3 prior to June 12. A lot of people in the Chicago area could not receive WBBM-DT, even within the city limits; in fact, that was the only
DTV station that most Chicagoans could not receive dependably. CBS applied to the
FCC to move WBBM-DT to channel 12, where it is now broadcasting. Reception has improved greatly.
WPVI-DT had to vacate its original digital channel, channel 64, as that is being reallocated to other services. But they will need to petition for another allocation in either the high VHF band or the UHF band. Channel 6 will not work, for reasons stated below.
The biggest problem with
DTV in this country is that the
FCC adopted the wrong standard and modulation scheme. I witnessed the demonstrations that Sinclair Broadcasting held in Baltimore ten years ago. For the demonstration, they used an analog station on channel 45 (WBFF-TV) and a digital station on channel 40 (WNUV-DT). One demonstration took place inside a condominium overlooking Baltimore's Inner Harbor. The windows faced away from Baltimore's TV tower. Using an indoor antenna, the analog signal was unwatchable, with multipath obliterating the sync pulses and causing the picture to break up. When the digital transmitter used the American 8-VSB
DTV scheme, reception was impossible unless the antenna was placed on the window ledge. If anyone walked near the antenna or touched it, the picture would break up and disappear. When the station switched to the European COFDM system, we had perfect reception no matter where the antenna was placed. When a technician disconnected the coaxial connector from the antenna, he got perfect reception when he touched the center conductor of the antenna cable! Sinclair petitioned the
FCC to adopt the European system, but was denied. Incidentally, the groundwork for that system was laid in Murray Hill, New Jersey, as OFDM (forerunner to COFDM) was invented in the 1970s by Bell Laboratories. Ironically, all digital studio-transmitter links and remote pickup systems (the microwave systems used for getting video from the news vans to the studio) use COFDM, even in this country!
Although the American
DTV system has improved somewhat, areas with a lot of multipath will still get lousy
DTV reception. Channel 6 is particularly bad for
DTV use, as it is adjacent to the FM broadcast band and strong FM signals may interfere with the
DTV tuners and converter boxes. The same interference that would put "worms" (diagonal lines that wiggle with the modulation on the FM station) on the picture of an analog channel 6 station will cause a complete failure of
DTV reception on that channel. In Philadelphia, WPVI-TV transmitted at 100
kW visual
ERP, which is sufficient to override FM interference within the city grade contour of the TV station. The low
ERP of the digital signal will not override this interference. Electrical noise, such as ignition noise from passing cars, will also cause dropouts in
DTV reception and low VHF channels are especially susceptible to this.
WPVI-TV was a cash cow for Disney/ABC. I wonder how long it will take for their advertisers to scream bloody murder due to the lousy coverage of the digital signal.
Folks, this is what happens when you have a Congress that is beholden to lobbyists and an
FCC that is run by lawyers, rather than engineers. Enjoy!
Less advertising throughout
Major Philadelphia station (6ABC) DTV broadcast power may not be enough
Linear Mode
