In article <telecom24.117.9@telecom-digest.org>, Michael Quinn
<quinnm@bah.com> wrote:
> Along this line, and at the risk of perhaps being slightly OT, if anyone
> knows why television uses channels while radio uses frequencies (for the
> most part, that is, the 88 channel) FM Marine Band in the 156 MHz range
> being an exception), I would be interested in hearing about it.
There's no intrinsic reason for using one form of naming over another.
However, note that _if_ you assign "channel numbers" to specific
frequency allocations, you are *permanently* fixing the utilization of
that chunk of RF spectrum. e.g. in going from 15khz deviation to 5khz
deviation on FM, you'd have to either completely 're-number'
everything, or you have non- consecutive "channel numbers" as you go
up the band.
When you (the regulatory authority) "haven't decided" what the minimum
allowable spacing between frequency assignments is, or even _if_ the
spacing between assignments will always be a multiple of that minimum
-- it is *really* difficult to come up with a channel 'number'.
[TELECOM Digest Editor's Note: This is an example of how someone
screwed up when the Citizens Band radio channels were numbered. CB is
allocated the space between 26.965 kc and (originally) 27.255 kc. The
'channels' were 10 kc apart, and there were (originally) 23 channels.
(Well, not originally, when there were 8 channels, but in later
years.) If you look at the difference between 27.255 and 26.965 as
divided in 10 kc increments you get more than 23. That's because the
FCC took three spaces in the middle and reserved them for use on
garage door openers. So we had channel 22 as 27.225 and channel 23
a full 30 kc later, on 27.255. Then the FCC said they would expand the
CB area all the way up to 27.405, or 40 channels, although common
sense would imply actually 43 channels if you take 27.405 minus 26.965
at 10 kc increments. What the FCC did, in an effort to 'tidy up' that
discrepany was run the channels slightly out of order. After channel
22 (27.225) they created channel _24_ at 27.235, channel _25_ at 27.245,
then they had the (already existing) channel _23_ at 27.255 where it
had always been, and then by 10 kc up to channel 40 at 27.405. Having
those two channels out of order in the frequency allocations did make
for some tricky programming of the 'gang switches' (revolving knobs
which select the channels). PAT]
Robert Bonomi (bonomi@host122.r-bonomi.com)