Vernall wrote:

[...]
Digital networking has been around for some 20 years, with A/D and D/A
conversion at the exchange.  Interconnections between exchanges and the
"network" are entirely with digital format, with data rates of 2 to 156
Mbit/s.  Subscribers still think they have an analogue connection, but it is
only as far as the exchange.  The likes of ADSL or ISDN bring digital format
into the subcriber loop, but that is additional to what I was mentioning in
my earlier comments.
[...]

Bob Vernall, Bob Riese and the group,
 thanks for the further explanations, which make a lot of sense.
I will pry my nose in my telephone line, to discover what 'horribilis' ghosts
are lurking there, hidden behind that reassuring and innocent tut-tut.
I will lightly couple the line with my new receiver, a JRC NRD-525, which,
BTW, seems to be very sensitive on LF, and should something unexpected
show up, it will be promptly captured and posted here.

73  Alberto  I2PHD