[sci.electronics] Help me g noise off modem line!

mulligan@coral.bucknell.edu (03/10/91)

I have a problem that soone out there may be able to help solve.  I use a
1200baud modem to connect a DEC VT100 terminal in my dorm room with the
main-frame on campus.  Noise on the phone line makes really strange stuff
appear on the screen sometimes.  (I can see a ~r in the last sentence that I
didn't type...line noise put it there!)  The receive data light on the modem
lights when it happens, so I feel my equipment is fine.


1.   I need info on ways to filter the "bad" stuff from the phone line.

2.   I'd really like to find a way to keep people from using call waiting on me
while I'm on the terminal.  They try to beep me, thinking it is another normal
phone call.  The beep really messes up the data stream.  I would think that
this would be harder to get around than the line noise.

I'm an E.E., so parts and construction are not a problem.  (Cost could be :) )

                                       Thanks!!!
................................................................................

Ed Mulligan                                      "What do you mean, there's
Bucknell University                               more to life than
mulligan@coral.bucknell.edu                       electronics and cars?"

dbell@cup.portal.com (David J Bell) (03/13/91)

Ed, I have good news and bad news....


>1.   I need info on ways to filter the "bad" stuff from the phone line.

This amounts to "black magic", I'm afraid; a great deal of the effort involved
in modem or other telecommunications development is solely to eliminate the
effects of noise. We all suffer...

>2.   I'd really like to find a way to keep people from using call waiting on m
e
>while I'm on the terminal.  They try to beep me, thinking it is another normal
>phone call.  The beep really messes up the data stream.  I would think that
>this would be harder to get around than the line noise.

Here's the good news!  Most (your's, I hope) phone systems offering call
waiting have a simple code you can send at the beginning of a call (before
dialing), that turns off call waiting, for the duration of that call.
In my area, it is '*70'. Just key this before dialing the mainframe, and
you should be safe!

Dave         dbell@cup.portal.com

terryb.bbs@shark.cs.fau.edu (terry bohning) (03/14/91)

dbell@cup.portal.com (David J Bell) writes:

> 
> Here's the good news!  Most (your's, I hope) phone systems offering call
> waiting have a simple code you can send at the beginning of a call (before
> dialing), that turns off call waiting, for the duration of that call.
> In my area, it is '*70'. Just key this before dialing the mainframe, and
> you should be safe!
> 

On pulse systems, it's 1170 (like the PDP).

scott@hpcvca.CV.HP.COM (Scott Linn) (03/15/91)

/ hpcvca:sci.electronics / dbell@cup.portal.com (David J Bell) /  5:12 pm  Mar 12, 1991 /

>Here's the good news!  Most (your's, I hope) phone systems offering call
>waiting have a simple code you can send at the beginning of a call (before
>dialing), that turns off call waiting, for the duration of that call.
>In my area, it is '*70'. Just key this before dialing the mainframe, and
>you should be safe!

Unless you're on a callback system :-(

wb8foz@mthvax.cs.miami.edu (David Lesher) (03/18/91)

The best solution for eliminating those call-interruption beeps
is to call the business office and get it removed. This works in
ALL CO's.

Then apply the savings toward a second phone line......

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