Quote:
Originally Posted by electroking
Hello all,
This thread is far from boring!
Someone mentioned earlier that the maximum number of VHF channels
in a given city would be 7. I assume that those channels would have
to be 2, 4, 5 or 6, 7, 9, 11, 13. Is that correct?
In case anyone is wondering, I have evidence of an actual case where
channels 4 and 5 are used, and sharing the same antenna as well!
The big diplexers are quite something to behold!
These two channels are separated by a guard band of 4 MHz, so they
can coexist in the same area, and at the same time they are close
enough that the same wideband antenna can be used (66-82 MHz)
These two channels are in use as described above in Quebec City.
Does anyone know of a similar installation elsewhere?
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I mentioned the maximum allowable number of stations in any given city is seven; the channels are 2, 4, 5, 7, 9, 11 and 13. Channels five and six cannot be assigned in the same city due to interference issues; this is also why either channel 5 or channel 6 (or both in some areas) is always vacant in any metropolitan area, and why most UHF television converters used these channels as their output frequencies.
Channels four and five can be and often were assigned right next to each other in the same area, however, because of the 4-MHz guard band you mentioned between the two channels (66-72 for 4 and 76-82 for 5). This situation exists in at least two metropolitan areas of the U.S. (New York City and Los Angeles) and also in areas such as Buffalo, New York which can receive a channel 5 station from outside the area (Buffalo itself has VHF channels 2, 4 and 7; the city is close enough to Toronto, Canada that channel 5 from the latter city is often received in Buffalo with a signal strong enough to watch).
Note as well that channels 13 and 14 can and sometimes were assigned adjacent to each other in the same metro area; this was possible because there is a much wider gap between channel 13 and channel 14 (254 MHz; 13 is 210-216 MHz and 14 is 470-476 MHz) than even between four and five, or six and seven (there is an 86-MHz gap between the latter two channels--channel six is 82-88 MHz and seven is 174-180 MHz).
UHF channels within the 14-69 range assigned in the same metropolitan area, however, must be separated by at least six channels to avoid interference between stations; that is, the nearest adjacent station to, for example, channel 14 would be channel 20 in a market with a channel 14 station and one on 20. The next available assignment in that market would be channel 26, and so on in six-channel increments, unless 26 was already in use locally; in the latter case the next station would be assigned on the nearest unused channel in that area.
I was in Princeton, New Jersey for my cousin's wedding in 1985. The motel I stayed in had a TV set (likely fed by a master antenna system) on which I could receive all seven New York stations and channels 3, 6 and 10 from Philadelphia as well. The reception from the Philadelphia stations was not perfect; there was a lot of adjacent-channel interference on channel 3 from New York's channel 2, on channel 6 from New York's channel 5 and on channel ten from New York's channel nine, but the stations were there nevertheless.