[clug] Telephone line voltage

Keith keiths at apex.net.au
Wed Sep 8 16:41:56 MDT 2010

	First my thanks to everyone who shook their heads over this and then told something of what 
fell out.  If I could take them one by one :

> So the telephone earthing could be good but your house earth could be bad.

	Good point - How can I check on that, please?  If I lift one corner of the house should I be 
able to see it underneath and then whack it back in a bit more firmly?

> > To really figure out what's going on, a decent CRO and an isolation
> > transformer are needed. The tranny is essential because your CRO will
> > happily try to ground the phone line via its power cord otherwise and
> > that would be Bad.

	What, please, is a CRO?  This sounds a bit beyond me.  In fact it sounds a lot beyond me - whom 
could I approach to come and do it for me?

> I'd agree with Michael - if it ain't broke, don't fix it.

	Well I have lost a mother board and an answering machine to unknown causes  ......

> The following wasn't written by me, as suggesting attaching anything
> to the phone line other that Austel approved equipment is a big no-no...
> So DON'T DO IT! Really!

	Point taken - so who could do it?

> Failing using a CRO, another diagnostic step would be to  <snipped>

	Again that all sounds very competent but is beyond me - could I invite anyone who could do it 
to come and try?  (Cups of tea galore to anyone who would ..... )

> I would like to eliminate any effects associated with the ADSL
> signals and to determine the frequency of any AC signals being "measured".

	Again, how, please?

> Steve and/or Keith,  could you explain (preferably  diagram) the test
> setup you're using?  What exactly are you measuring the voltage across,
> for example?

	The line coming in from the pit outside ( a side story as to how that was located) terminates 
in flat box on my skirting board.  It has one female socket into which I normally plug a 'one in, 
three out' adaptor.  From that one line to the modem, one to the answering machine and the third to 
the telephone handset.  In the meantime to the contacts to which the incoming line is attached is 
attached another 'pair' cable which goes back out the box the same way, turns up inside the wall 
behind, across the roof space, down inside the wall between the living room and the kitchen and 
emerges through the kitchen wall into a wall-fastened back plate.  Onto that I fit a wall telephone.  
So effectively that kitchen phone is connected directly to the outside wire.

	To run the test : first that kitchen phone is removed - i.e. not just taken off hook but the 
whole instrument lifted off the plate, unplugged and laid aside.  Then the one-in-three-out adaptor 
is removed.  So now I have just a single female socket.  Into that I put a length of telephone cable 
approx 5' long with a 'standard' square plug at each end.  (Not sure of the technical name for that 
but the square shape that clips into the female socket at the back of a telephone instrument, 
answering machine, etc.)  The other end of the cable I bring up to my table top and tape down so the 
two brass strips which constitute the contacts are uppermost.  Switch on the test meter (Q-1419 from 
Dick Smith Electronics) and carefully put one probe onto one brass contact and the other on to the 
other, taking care that they do not touch each other.  Take the reading.

	Hope that makes sense  ......   ;-)=

> Reliable connections and repeatable measurements are possible.

	Have done - I think.

> one possible explanation is:  "message waiting" light is driven form the
> exchange, and it will use 110 to 120 V pulsed DC to blink the messaage
> waiting light...

	But too much of a coincidence, surely for that to happen repeatedly?  And would not 'message 
waiting' be activated only when I am on a call and another one tries to come through?

> So perhaps the person who had repoted this issue has in fact turned on
> message bank with telstra...

	Not me - I do not use message bank.

Keith Sayers                                        keiths at apex.net.au
6 Clambe Place,
Australia                              http://www.apex.net.au/~keiths

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