DevilsPGD <devilspgd@crazyhat.net> wrote:
> Shaw cable is (or was, I don't have my TV connected to my
> DCT right now) using channel 1 as a digital channel for
> themselves. Analog cable still starts at 2 though.
Whereupon Doug Krause <dkrause@ratcage.com> wrote:
> Comcast in Western Massachusetts uses channel 1 for On Demand.
"On Demand" is distributed digitally; as DevilsPGD noted, channel 1
can be used for digital services. However, digital "channel" numbers
are arbitrary labels for specific data streams; they bear no
relationship to any actual RF channel.
Based on the "channel" number, a digital converter refers to an
internal lookup table. Based on the information obtained from the
table, the converter determines if the signal is authorized; if so, it
tunes to the correct RF carrier, demodulates it, demuxes it, decodes
the desired signal, and outputs video and audio. Most converters
include a modulator to provide an NTSC output, typically switchable to
Channel 3 or 4. Most converters also display the digital "channel"
number; some display additional information such as time and date
and/or program metadata.
Lookup tables can be downloaded from the cable TV company headend to
accommodate changes in authorized service levels or to totally
de-authorize a non-pay subscriber.
> About 10 or 15 years ago my grandmother's cable in Arlington,
> Texas had Channels 1, 0, and 00.
Settop converters of that vintage were analog. Analog cable TV channel
numbers were not standardized until 1992, when the FCC adopted EIA Interim
Standard IS-132 [47 CFR 76.605(a)(ii)]. See
<http://www.annsgarden.com/telecom/CATV.html>.
Long before 1992, most analog cable-TV channel numbers had been fairly
well standardized by common industry practice. Two numbering systems
were in common use:
Letter designations: A, B, C, etc. Channel A = 120-126 MHz.
Number designations: 14,15,16, etc. Channel 14 = 120-126 MHz.
But three channel numbers had remained unstandardized, so various converter
manufactures invented their own numbering schemes:
FREQUENCY EIA LETTER OTHER CHANNEL NUMBERS
BAND CHANNEL CHANNEL SOMETIMES USED BY
(MHz) NUMBER NUMBER CONVERTER MANUFACTURERS NOTES
--------- ------- ------- ------------------------ -----
72-78 1 A-8, 0, 1 1,2
108-114 98 A-2, 0, 1, 00, 01, 54, 57, 60 1,3
114-120 99 A-1, 0, 1, 00, 01, 55, 58, 61 1,3
Note 1: "A-8" is read "A minus 8," meaning eight channels
below channel A. Similarly, "A-1" is one channel below
channel A, etc.
Note 2: The IRC and HRC frequency plans expand the 72-76 MHz
band to 6 MHz, enough to carry one NTSC television channel,
designated by EIA as Channel 1. See <http://tinyurl.com/4wpqr>.
Note 3: The 108-120 MHz is used in the airspace for VOR
(VHF Omnidirectional Range). To avoid a possible conflict,
this band was skipped when the original lettered-channel
assignments were made (sometime around 1960). As technology
improved (and FCC rules changed), this band became usable for
two TV channels, which somehow got named A-2 and A-1. For
obvious reasons, converter manufacturers didn't want to use
such klunky channel numbers, so they invented their own numbers.
The EIA standard finally put an end to this nonsense by naming
them 98 and 99.
Your grandmother's Channels 1, 0, and 00 were probably some
combination of what are now EIA Channels 1, 98, and 99. But, given
the free-for-all channel assignment schemes floating around back then,
about all we can say for certain is that Channel 1 was *not* the same
as the long-defunct broadcast Channel 1.
Neal McLain
Neal McLain (nmclain@annsgarden.com)