>> I wonder how they're modulated.
>> Can any other reader answer this question?
> Quadrature modulation using many channels. Look here:
>
formatting link
> Dave Grebe
Wow! No wonder most people don't go into detail!
Here's a quote from the introduction:
"Although many system designers are competent and comfortable with DSP and all th> Choreboy wrote:
> A carrier vor V.90 must have some very precise modulation. It's
>> amazing that an 8kHz sampling can capture it well enough to be
>> useful.
> Frequently it can't, which is why your modem downgrades to a slower > speed.
>>> All of these noise sources collectively impair the ability of the loop
>>> to carry DSL signals.
>> Local loop cables (trunk cables?) seem to deteriorate. Phone men seem
>> to look for available pairs when customers complain of noise. I
>> wonder if voltage from nearby lightning strikes might cause pinhole
>> damage to the insulation of twisted pairs, and over the years it gets
>> hard to find a good pair.
> Nearby lightning strikes likely would do a lot more than cause
> "pinhole damage." But you're right about telco cables deteriorating
> over time. Water intrusion can cause severe interference ("every time
> it rains, I get static on my telephone!").
I wonder if old cables have been analyzed to see why they went bad. Lightning-related voltage spikes can damage semiconductors although the damage may not be apparent. I wonder if that could happen to the insulation on telephone conductors.
> Load coils might be one reason a particular phone sounds distorted at
>> a particular location.
> I doubt that, but I guess it's possible.
If the capacitance were lumped, it and an inductor would form a tuned tank. I suppose it's about the same with distributed capacitance. The tank would have high impedance at one frequency and lower impedance at higher or lower frequencies. The broadness of the curve would depend on the resistance in the coil and maybe in the line. An uneven frequency response could make it hard to recognize who's calling or understand his words.
> Across the street, a small trunk line (cable with lots of wire
>> pairs) comes from the aerial terminal down a couple of feet to a
>> fusebox on the utility pole. (I think the telco calls them something
>> besides fuses.) The drop cables come out of that box. Probably >> just a junction box.
After lightning knocked out my phone service, a telco man opened the box and replaced what he called a fuse. Those fuses have another name I can't remember.
>>> Think what would have happened if RG-59 hadn't been invented.
>>>> Everybody would have used RG-6, which looks nearly the same but
>>>> attenuates uhf much less. With better reception there would have
>>>> been more uhf stations and less demand for cable.
>>> As a former cable guy, I don't agree with that. Many UHF stations
>>> depended on cable TV systems to distribute their signals throughout
>>> their "specified zones" (which, back in the '60s and '70s, was a
>>> 35-mile radius around the city of license). This was particularly
>>> true in mountainous areas where cable T systems carried UHF signals
>>> to specified-zone communities that were beyond the reach of their >>> transmitters.
>> With a bow-tie antenna, a good UHF amp, a rotator, and RG-6U, we could
>> receive so many channels that we weren't interested in cable.
> Well, obviously you don't live in a place like Mahanoy City
> Pennsylvania, Tuckerman Arkansas, or Astoria Oregon -- places where it
> simply isn't possible to get any station -- UHF or VHF -- off the air.
> Cable TV started in all three of those communities in 1948, and all
> three still claim to have been first.
> Neal McLain
> [TELECOM Digest Editor's Note: And don't forget Independence, KS where
> until cable came along (via Time Warner in the 1980's) our television
> reception consisted of TWO channels; channel 6 and channel 9, but only
> one of those two if you wanted a good picture. Most people had very
> _high_ antennas on their house if they wanted television, and they
> compromised by using a 'rotor' attached to their TV set to turn the
> rooftop antenna one way or the other. If they could not afford the
> rotor, then they left the antenna turned sort of in the middle and
> lived with that. We got one station from Tulsa, Oklahoma (80 miles
> almost straight south) and one station from Joplin, Missouri (90
> miles more or less straight east.) Around here, 'big city' (as in
> presence of television stations) means Wichita, KS which is 110 miles
> northwest, or Topeka KS which is about 150 miles straight north, and
> we could not get those stations very well at all in those days. PAT]
In 1956 I moved to Rutland VT, in a valley. We had three floors above the basement, and the peak of our slate roof may have been forty feet above the ground. On the peak was a mast with guy wires. There were three antennae on the mast, one pointed to Burlington 70 miles away, on to Albany 90 miles away, and one to Boston 160 miles away. Three cables led from the antennae to a switch on the back of the TV.
The snow was bad all year. Community cable, with an antenna mast on a nearby mountain, was discussed. A year or so later, Lucky 13 started in Albany. In spite of the distance and the mountains, it came in without snow. I heard no more about community cable.
I don't know how much it cost to operate a small UHF station, but in Rutland I think it could have been started and operated much cheaper than cable. The audience would probably have needed something besides a loop on their TV, and I suppose advertising would have had to support it.