Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!cs.utexas.edu!uunet!mcvax!ukc!axion!galadriel!pcf
From: pcf@galadriel.bt.co.uk (Pete French)
Newsgroups: sci.electronics
Subject: Re: MODEM SPEED INCREASE
Message-ID: <324@galadriel.bt.co.uk>
Date: 18 Aug 89 08:00:14 GMT
References: <1436@esunix.UUCP>
Organization: RT6115, BTRL, Martlesham Heath, England
Lines: 34

From article <1436@esunix.UUCP>, by hcooper@esunix.UUCP (Harrison Cooper):
> 
> The question is can they be upgraded to 1200 or more?  I have posted
> this before I have opened either one up, so I don't know what devices
> they are using.

You will need to change the filters , the oscillators and the demodulator.

On an old modem you may have a chance. The filters can probably be changed
by simply altering all the resistors and capacitors around them. This will
then allow you to use the FSK tones necessary for the different standard.

The oscillators can probably bo modified similarly to generate the necessary
tones when presented with a mark or a space. It depends upon how they are
constructed...

The major problem will probably be with the demodulation. If this is just
done with a pair of filters then you may have a chance... however it is most
likely to be done with a PLL or similar in which case its "data sheet time".


If you open it up and its an all-transistor and relays unit then you may
have a chance. If its got any IC's in it then forget it. Its easier to
build your own from an AM7910. You could probably salvage and Level Shifting
circuits for the RS232 and the coupling to the line - but trash the 'tronix.

			-Pete.


-- 
       -Pete French.               |
  British Telecom Research Labs.   | "The carefree days are distant now,
 Martlesham Heath, East Anglia.    |  I wear my memories like a shroud..."
All my own thoughts (of course)    |                               -SIOUXSIE