"spamtrap1888" wrote in message
...
On Jun 21, 7:12 pm, Robert Macy wrote:
On Jun 21, 6:05 pm, "Arfa Daily" wrote:









wrote in message

...

Ok, I set up a 2p2t switch that turns off my in-home lines and
instead
goes to an
RJ11 jack. The telco says I should test this to see if the problem is
mine
or
theirs. SO far this is SOP.

So then me thinks, why should I have to scramble for a tel set to
make a
test? Why not just put an LED there? So I need a 2700 ohn resistor
in
series with the LED. I can still plug in the tel set, but the LED
will
tell
me immediately what is going on as soon as I swich from whole-house
to
test-circuit.

- = -

You would still need to watch out for the AC ringtone, as this will try
to
stick a huge reverse voltage across your LED on every half cycle. Your
resistor can be much higher than 2.7k with modern high efficiency LEDs.
I
think I would go for around 10k as the series resistor, and also put a
1N4007 diode in inverse parallel with the LED. Of course, this only all
works at all, if your telephone operator doesn't use line polarity
reversal
for line status signalling. It's been a lot of years since I learnt all
this
stuff at college, but I seem to recall that this used to be the case -
at
least here in the UK anyway - and was the reason that there was a
bridge
rectifier in the telephone, so that the polarity inside remained the
same,
irrespective of what was going on polarity-wise on the line. Perhaps
Robert
would be more current on that.


Here in the US the telco sometimes would also do line reversal AFTER
you acquired the connection! Translates to Touch Tone Dialer didn't
work anymore! I haven't heard of it happening lately, but moot point,
every phone I've seen simply bridge rectifies and is done with it.

My 1970s WECo phone will not generate dialing tones if tip and ring
are reversed -- no rectifier there.

When I worked for the telephone circuit company, two-party lines had
tuned ringers: 20 Hz for one party and 30Hz for the other. Is that
what line reversal was used for in the UK? to distinguish between
parties? Here you had to go to single party service if you wanted
touch tone dialing.


I honestly can't remember why it was done. I never worked directly in phone
service provision, but back 40 years ago, college courses were 'well
rounded' affairs, and as well as the radio TV and electronics course that
was my primary module, we also had classes in math and telecom principles.
As an apprentice, I did a full 12 hour day at college, one day per week, for
five years ...

However, as Robert says, I seem to recall that the line reversal took place
after connection acquisition, and was for some kind of signalling purpose.
Maybe, it was used by other equipment in the chain to determine that the
line had been looped ?

I don't recall ever being taught anything about how party line routing
worked here, but it does seem as though that might be a valid way of using
line reversal signalling. There is an ex British Telecom engineer lives a
couple of doors up from me. He was an exchange engineer as far as I recall,
so I guess he should know the system backwards. Next time I see him out in
his garden, I'll ask.

Arfa