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.
Robert Bonomi (bonomi@host122.r-bonomi.com)