I wrote [TD V23 #525]:
> However, I still think that in the specific case at hand the
> Coffeyville TV station was probably the primary reason for not
> using cable channel 4 [in Independence, Kansas]. Given that
> channel 4 is subject to interference from a television station
> (even a weak one like W04EJ), it seems unlikely that the cable
> company would have used that channel for an important service
> like HBO or Showtime.
Whereupon DevilsPGD <email@example.com> wrote [TD V23 #526]:
> Could it be that there wasn't a conflict at that time?
According to PAT, channel 4 was in use in Coffeyville as far back as
1954-55 [TD V23 #519]:
> I seem to remember channel 4 from *years* ago when as a young
> kid I lived and visited in Coffeyville. It seems to me it was
> a 24 hour per day transmission of some weather station. The
> cameras always looking at the weather dials, and background
> music. That would have been 1954-55. PAT]
> Channel 4 isn't used for anything important here, just text
> news last time I checked, but the picture is clear and sharp.
Is there a local broadcast station on Channel 4 where you are? If so,
that would be consistent with the cable company's use of cable channel
4 for a relatively unimportant service like "text news."
It's certainly possible for a cable company to use a cable channel
that conflicts with a local off-air station; indeed, that's the ideal
situation. But the fact remains that in some situations, off-air
interference *does occur*. For that reason, a cable company isn't
likely to use it for an important service like HBO or Showtime.
The two most common sources of off-the-air interference into a cable
A LEAK IN THE CABLE NETWORK. Theoretically, cable TV systems are
fully-shielded, closed networks. Nevertheless, breaks in the shield
("leaks") are inevitable. Searching out and fixing leaks is the cable
company's responsibility, strongly enforced by the FCC. See:
Leakage sources: http://www.sbe24.org/archive/c24aug98.asp#six
Leakage control: http://www.sbe24.org/archive/c24sep98.asp#six
FCC enforcement: http://www.sbe24.org/archive/c24oct98.asp#six
FCC enforcement: http://www.sbe24.org/archive/c24nov98.asp#six
DIRECT PICKUP (DPU) IN THE TELEVISION RECEIVER. Back in the 1950s and
1960, cable companies usually didn't provide converters; the incoming
cable was connected directly to the TV set. TV sets in those days
were generally poorly shielded (300-ohm twinlead was often used to
connect the setback terminals to the tuner). This situation resulted
in DPU: direct pickup of the off-air signal by the internal circuitry
of the TV set.
The introduction of converters solved the DPU problem (assuming that
the converter itself was properly shielded). Of course, the converter
output had to be on a channel that wasn't subject to DPU. To
accommodate this situation, converters were fitted with dual-channel
modulators, so that a vacant local channel could be selected. Most
converters could be switched between channel 3 or 4; Pioneer
converters used channel 2 or 3.
So if your cable company's channel 4 is "clear and sharp," that's
great: it means your cable company is doing a good job with leakage
control. But I still wouldn't use it for HBO.
[TELECOM Digest Editor's Note: But this area did not have cable TV
(nor, for the most part) any over the air TV in 1954-55. Coffeyville
had that *one* station (channel 4) over the air in that time period,
Independence had nothing. Even today, Coffeyville and Independence can
receive at best *two* over the air television signals, one from
Joplin, MO/Pittsburg, KS (90 miles straight east), and one from Tulsa,
OK (85 miles almost straight south), and possibly a third one from
Wichita, KS (110 miles northwest). Those are our three 'major'
cities. Coffeyville of course still gets channel 4 with its weather
dials, etc. Your choices here are (a)cable (b) *very high* antenna
most likely amplified or (c) nothing at all. On over the air signals,
the two out of the three possible depends on how your antenna is
turned. Turned sort of east and south for Joplin and Tulsa, or sort
of east and south for good Tulsa and crappy Wichita. When cable moved
into rural southeast Kansas in the 1970's, we had Time-Warner's prede-
cessor. Then Coffeyville about 1990 got Cox Cable. In 2002, Time-Warner
traded their territory here to Cable One in exchange for some larger
area which they wanted (and Cable One) had. Our cable also serves the
little towns of Neodesha, Kansas and Cherryvale, KS which are near
here. Cox Cable has Coffeyville and all the southern part of the