Ian Jackson wrote in
:

Are you confusing the internet being carried (like cable TV) over coax
at RF, and via ADSL on twisted-pair phone lines? The coax drop cables
are usually RG6, which has a copper-plated steel inner.


I was likely confused enough to not know what I was confusing, but I do
remember it was about 40MHz or so (actually I think 36 to 39) which fits what
you said below.

If it's anything like some coax I worked with in the 60s, there might be
a small 'kink' in the frequency response* at around 40MHz, which is
probably the frequency at which all the RF has moved out of the steel
core, and into the copper plating.