In message , Reg Edwards
writes
"Richard Harrison" wrote in message
...
Reg wrote:
"How does each repeater generate its unique pilot tone when a trawler or
earthquake breaks the inner conductor?"

Well, I`ve checked and find that some subsea multiplex units do generate
pilot tones for the purpose I speculated and for others. There is an
"SD" model equipment in which each group modulator generates a pilot
tone used for switching, level adjustment, equalization, etc. If these
tones are being recorded and start losing power, I expect they fade away
but die all at once when the path is interrupted. By examining the
record, it should be possible to see which tones suffered sudden death
and which faded away. There is capacitance in the system and the power
is high-voltage and low current. My information says there is 5500 volts
at each end of the transatlantic cable and that the system current drain
is 389 milliamperes. It has 182 repeaters spaced at about 23 miles. An
equalizer follows each 10th repeater.

I have experience doing similar things with terrestrial radio multiplex.
We used cheap pressure stamping Rust-Rack event recorders to record
breaks in pilot reception. I`ve pored over years of these records, 24
hours at a time.

Best regards, Richard Harrison, KB5WZI

=======================================

OK, Richard, so we've located by some automatic means the cable damage to be
somewhere between the n'th and (n+1)'th repeaters. This is nowhere good
enough for the repair ship captain. He wants to be back in port again for
Christmas. And it costs a million dollars in lost revenue each day the cable
is out of service plus the cost of keeping an 8000-ton ship and its crew at
sea.

The repair ship is just leaving Southampton docks. There's an Atlantic storm
brewing. There are spare lengths of cable and repeaters aboard. This time
they remember to collect the cable jointer. The ship's doctor retires to his
cabin as he is always sea-sick. The ship's Chief Engineer Officer, always a
Scotsman, and the Cable Testing Officer, neither of whom ever seem to have
anything to do, are outside the duty-free bar waiting for it to open.

The captain is pacing up and down the bridge waiting impatiently for a radio
message, cursing the poor fellow at the cable terminal station 500 miles
away on the Scottish rocky Atlantic coast, who is sweating blood twiddling
knobs trying to balance the wideband, 0.05 to 50 Hz, reflection-coefficient
bridge to within plus or minus 0.1 miles along the articial line and
adjusting the artificial fault (R and C in parallel) to within 10 ohms with
a biassing current of 50 milliamps.

After another couple of hours with a sliderule, correcting for seasonal
water temperature, etc., he changes his mind for the tenth time, takes
another swig of scotch, plucks up courage, swallows, and calls the operator.
He asks to send an urgent radio telegram to a cable ship heading westwards
down the English Channel. The message is brief, polite and states "Fault
estimated to be 623.7 miles from Oban". The captain issues a brief
instruction to the duty officer and retires to the loneliness of his cabin.

It is deep dusk. The lights of Plymouth from where Drake set sail 400 years
before can be seen on the starboard horizon. The radar ppi display in the
darkness of the bridge sweeps round monotonously every three seconds clearly
displaying a dozen merchant ships sharing the roughening waters.

The ships engines quietly, monotonously, emit a steady thud, thud, thud,
thud . . . . . . until they merge unnoticed into everybody's
unconsciousness and on deck only the sea and wind can be felt and heard.
----
Reg.





Reg. Please be careful. I nearly choked with laughter on my cornflakes
as I read this this morning. Whatever you are taking, do I need a
prescription, or can I get it over the counter? A great start to the day
(but I'd better get my tax return done before the deadline of the end of
the month).
Ian.
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