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From: wtm@neoucom.UUCP.UUCP
Newsgroups: mod.telecom
Subject: Re: phone line surges and spikes
Message-ID: <8607010606.AA20591@ucbvax.Berkeley.EDU>
Date: Fri, 13-Jun-86 00:15:16 EDT
Article-I.D.: ucbvax.8607010606.AA20591
Posted: Fri Jun 13 00:15:16 1986
Date-Received: Tue, 1-Jul-86 18:41:42 EDT
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The author of the original article mentions hearing chips from his 
cheap phone at about 1:00 am. Sounds like an automated test procedure 
being run on his loop.

Where I live is what used to be Bell territory. I think we have ESS-IV 
(but I'm not sure, so please no flames, I'm ignorant). I've noticed 
that regularly at 2:30 a.m. my circa 1930 Stromberg-Carlson crank phone 
emits a single "ding-dong", while all the other phones are silent. I 
think that it's bell coil and coupling capacitor have a low enough 
frequency response to pick up the polarity reversal of some kind of 
automated subscriber loop test.

Now for the real question. Ma Bell has a protector block where the line 
comes in the house. Everybody has these, as this is regulated by law as 
well as internal telephone edict. Basically, the protector is a spark 
gap(s) and silicon resistors that blow when the gap sparks, thus 
isolating the network from you. Sorry if the descirption isn't 100% 
correct--this is the kind I know, but there are several types of 
protectors around. I'm describing mine, which was installed in 1929.

Point is, the protector block is really more meant to protect the 
network from you rather than you from it. You might want to consider 
some additional protection. A gas discharge tube is the best way to go, 
as it responds quickly enough to present a reasonable amount of 
protection. Several places sell phone spike protectors, which are 
actually gas tubes in little plastic boxes sold at considerable mark-
up.

Since modems mix outside power & electronics with Ma Bell electronics, 
they are quite closely regulated and scrutinized. Of course, in these 
days of deregulation and Hong Kong imports, there may be some laxity in 
quality control of off-brands. As long as you have a major brand modem, 
you can probably be reasonably assured that it already has mov and/or 
gas tube protection inside. (I've torn quite a few apart, and so far 
all the ones I've seen have it!) Note that a gas tube often looks like 
an overgrown ceramic diode with glass/metal seals on the ends. Check 
your modem.

Most of all beware about what you connect to your phone line. It sure 
isn't cool the screw up the network by attaching a weird device. You 
might possibly screw up your neighbor's line too if you goof up--this 
is because many lines are spilt by using duplexing transformers. (This 
practice is common in my neighborhood which is fairly old, and has fews 
lines.)

By the way, 2 years ago my house had a direct lightning hit. It blew up 
part of the chimney and shattered a big mirror (due to current flow in 
the silver heating the glass). Several of the light switches were 
vaporized. At the time, I had three Bell phones and a cordless. The 
three Bell phones and protector block were o.k., but the cordless was 
fried. (There were just two wires sticking out of the pc board where 
the MOV used to be!) Needless to say, everytime there is a 
thunderstorm, I still get a little nervous now! (I was home at the 
time.) ~~Bill

Bill Mayhew -Elec. Engr.
Div. Basic Medical Sciences
N. E. Ohio Coll. of Med.
Rootstown, OH  44272  USA  (216) 325-2511
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