bz wrote:
The 5000 foot cable will start with twice the number of dB loss as the 2500
foot cable.
Therefore the change per degree will be twice as much, automatically.

One would hope, but it is not true. Everyone so far has assumed that
coax is a pipe with smooth sides. Put something in and it slows down
because it rubs against the sides, but it comes out basicly unchanged
with a linear degradation.

The problem is that coax is more like a set of one wavelength pipes with
an incomplete one at the end. How this effects the signal is dependent
upon the frequency.

If the coax is used for close to one frequency, such as a single channel
carrier, the effect will be the same. As the length approaches 1/2 wavelength
there will be more antenuation, but since it effects the single carrier
nearly the same amount, there will be minmal phase and linerarity distortion.

If the signal were on the other hand a baseband video signal, or a group
of channels such as an analog cable tv system with 200 channels ranging
from low band VHF to high band UHF and anywhere in between, it becomes
more complex.

These days, it's not as much of a problem as digital video is carried over
a few analog channels, and they are close in frequency.

It was also far more critical in the early days of color TV since there
were no such things as phase locked loops and other methods of decoding
a phase modulated signal without compensating for distortion.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM