In article <telecom24.122.10@telecom-digest.org>,
Michael D. Sullivan <userid@camsul.example.invalid> wrote:
> A simpler explanation for the use of channel numbers for TV and
> frequencies for FM and AM radio is that (1) AM radio operated in a
> contiguous band covered by an analog variable tuning capacitor and
> never had separate channel numbers, so (2) people were used to tuning
> in radio stations by frequency on a dial, and (3) FM radio likewise
> was in a contiguous band covered by a an analog variable tuning
> capacitor, so people were comfortable tuning in the station by
> frequency.
> Television, on tho other hand, started out in two discontiguous VHF
> bands, with somewhat variable spacing between channels and a need for
> precise tuning, and tuning in on a single band by twiddling an analog
> variable tuning capacitor to the right frequency would have been
> difficult. This tuning method was used on some early TVs; I don't know
> whether they were tuned by numeric frequency or by channel number, but
> it would not have been very convenient. The TV industry instead
> standardized on TV tuners that had 12 discrete fixed settings, pre-tuned
> to channels 2-13, with a fine tuning control that allowed one to tune
> the frequency higher or lower to account for offsets. Later on, tuners
> had separate fine-tuners for each channel so one wouldn't need to retune
> when switching from station to station. Given the move to fixed-
> position tuning, the use of "digital" numbering of channels instead of
> analog-like frequency designations was an obvious simplification.
Plausable, just 'false to fact'. <wry grin>
In the early days of TV receivers, they were equipped with continuous-
tuning knobs/dials, just like an AM radio receiver. For the TV band,
however the indicator assembly was marked by "channel", *not* by
frequency.
I used to have a 1930's Crosley TV that had that kind of continuous
tuner. *BIG* gap on the dial, between channel 6 and 7, It actually
tuned across that entire 'midband' space -- with all kinds of
interesting results. You could "see" aircraft band transmissions, and
hear stuff on broadcast FM, 2m Ham, and business-band.
[[.. munch ..]]
> [TELECOM Digest Editor's Note: This is true, however if you look at
> some FCC documents on FM radio frequency allocations (for example,
> documents on which frequencies are available on which places for
> 'low power' FM). All those documents show both 'frequency' and
> 'channel number' for the spaces between 87.6 FM and 108.1 FM. I
> think they have the 'channels' beginning at 201 and numbering
> upward. PAT]
Originally, 199 channels, 100kc spacing, numbered 1-199, corresponding
to frequencies from 88.1 through 107.9 megacycles. Since then, even
the name of the unit-of-measurement has changed. :) and a few
additional channels have managed to sneak in. I believe 200 is 108.0,
201 is 88.0, and I'm not sure how they numbered the space below 88.0.
[TELECOM Digest Editor's Note: I seem to recall about 1960 or so there
was a 'christian' radio station in Hammond, Indiana which belonged to
Crawford Broadcasting Company (WYCA perhaps?) which was horribly over-
modulated most of the time and located somewhere in the 89-90 megs
territory on the FM band. Many people did not have FM radios in those
days, but the standing joke was you did not need to purchase an FM
radio to listen to it; all you had to do was tune your television set
to channel 6 (no such channel then or now around Chicago) and tweak
the dial slightly in order to pick up WYCA clearly. About 1989, I
wrote a piece here in the Digest about that horrible station and all
the interference they caused in the North Hammond/Burnham, Illinois
area; the FCC finally required the station to work with Illinois Bell
to install filters free of charge on people's phones and other types
of amplifier equipment on request. PAT]
Robert Bonomi (bonomi@host122.r-bonomi.com)