Date: Thu, 07 Jan 93 21:00:32 GMT
From: rice@ttd.teradyne.com
Newsgroups: comp.dcom.telecom
Subject: Re: Why Does Phone Bell 'Ping' on a Regular Basis?
Organization: Teradyne Inc., Telecommunications Division
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 13, Issue 15, Message 6 of 10

In article <telecom13.8.9@eecs.nwu.edu>, glenn@rigel.econ.uga.edu
(Glenn F. Leavell) writes:

> My parents live in Mississippi and get their local phone service from
> South Central Bell.  According to my parents, the bells in their
> phones make a 'ping' every evening around 10:15PM.  They say that the
> ping almost always occurs around the same time, but that on certain
> nights it may not occur until close to midnight.  They've called South
> Central Bell about this, and they were told that the ping was NOT
> occuring due to anything that the phone company was doing.

This, not uncommon, occurrance is caused by automated line test
equipment. The real clue is the fact that it happens every night at
about the same time.In SCB it's probably MLT or MLT2. This equipment
can be set up to routinely test each line in an office, every night on
a regular schedule.

The phenomena is known as 'bell tap'. When the line is tested, it is
disconnected from the line finder, or line circuit, which provides
dial tone, for the one or two seconds that it takes to perform the
parametric measurements on the line. These tests are usually done at
low voltage (10-20v) and won't usually cause a phone to ring.

When the line is re-connected to the line circuit, -50v is placed back
on the line. The 50v is sometimes enough to cause the ringer magnet to
pull the clapper against the bell, one time. Also in some of the
'cheepie' phones with electronic ringers, the sounder will 'cheep'
once when voltage in initially applied (re-applied).

One solution to the problem is to reverse tip and ring on the phone
(reverse the red and green wires at the connector block.  This causes
the magnet to kick the clapper the opposite direction when voltage is
initially applied.  This will usually work, but if the phone is an
older touch tone phone, this may cause the T.T. Pad not to work (they
were polarity sensitive in older Bell Phones).

Also, it's sometimes possible to mechanically adjust the bell, so that
the -50v pluse isn't quite enough to pull the bell magnet enough to
cause a tap.

With the advent of automated line test equipment in the past 15 years
or so, this has been an on-going problem. It's much more prevalent in
Europe, where telephone instruments are of generally higher impeedance
and it takes much less voltage to ring the phone.

On the other side of the equation, the automated testing allows the
telco to recognize deteriorating outside plant cable in many cases
before the customer even recoginzes that there's a problem, and fix
it. Often out of service lines are reported by the equipment and
repaired with the customer never being aware of a problem.  A
deteriorating cable or cross connect box that could ultimately result
in 20-50 subscriber trouble reports can often be found, diagnosed, and
repaired before any customer reports occur, so that grade of services
is improved overall. (And it's less expensive to do it that way then
respond individually to each and every call as they occur), thus
everybody saves.


John Rice        K9IJ     |  "Did I say that ?" I must have, but It was
                          |   MY opinion only, no one else's...Especially
                          |   Not my Employer's....
rice@ttd.teradyne.com     |   Purveyor of Miracles,Magic and Sleight-of-hand