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Re: UO-11 receive MODEM's



Douglas:

> heh , don't laugh Larry , we use those 202t modems in our 911 phone
> switch ( Teltronics ) for linking to the ali database provider , and
> they were brand new just  two years ago , we will need more when we
> build our new center , so if you know of this cheap source next year let
> me know ;^}

No, I would not choose to do that and I strongly recommend you reconsider
your use of these devices in todays world.  You should be aware that the
telephone network has lost all sense of distortion sources that we use to
work our fingers to the bone trying to manage.  Envelope delay distortion is
not even measured by most of the newer telephone network devices today and
further the absolute delay distortion is highly variable throughout the
network with the hodge podge of transmission devices.  The 202 family of
MODEM's  requires, repeat requires, a defined and very narrow limits of
enevelope delay distortion, sometimes called quaintly "twist" and the 202
modem is absolutely incapable of coping with changes in absolute delay.  For
a 911 service the use of such devices in todays network is both unwise and
would no longer be good engineering.  I urge you to reconsider using such
devices today.

All this being said, I once sat on a beach in Hawaii with a Yeasu 726 trying
to talk to UO-11 shortly after launch and nearly went nuts trying to upload
a message to the satellite to demonstrate the DCE - the problem was delay
distortion in the 726 modulator........

I was looking in the junk around here this morning and found several of the
202 type demodulators we built so many years ago, they are complex looking
pieces of work, so many discrete components in that time - better now to get
an EXAR chip I suspect.

Larry
VA3LK



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