Aucbvax.6656
fa.info-terms
utzoo!decvax!ucbvax!info-terms
Fri Apr 9 10:59:22 1982
Re: VADIC 3400 series modem
>From csk@UCLA-Security Fri Apr 9 10:56:40 1982
You don't seem to understand the difference between the signalling
technique and the speed. All characters are sent bit at a time.
Using the 300 baud signalling technique (frequency shift keying),
one frequency is used for a zero bit and one frequency for a one
bit. Because of the frequencies used, and the limitations of the
phone system, this is limited to about 600 baud. A different
technique (I am not sure of the proper name but I call it di-bit
phase encoding) is needed to function properly at 1200 baud.
However, the important point is that there is still some way
of representing a 1 bit and a zero bit. Now, if you transmit
using the 1200 baud signalling technique at 300 baud, you are
not doing anything to improve noise rejection! You are just
sending the bits out slower! In fact, the 1200 baud technique
was optimized for transmission at 1200 baud only and you will
get MORE noise when the bits are fed to the modem at 300 baud!
If you are having trouble at 1200 baud, you can:
1. try another modem
2. switch to 300 baud and get a 300 baud modem (using the standard
300 baud signalling technique)... this may or may not help
3. try talking to another site to see if it is your modem, the
computer's modem, or the phone system
4. spend lots of money for a conditioned phone line
5. give up.
p.s. the direct connect 1200 baud vadic modems work a lot better
(usually) than the acoustic coupled 1200 baud modems. also,
usually the vadic 1200 baud system works better than the bell 212
system, but, if you have access to some of those, you might
try those and see if it helps (unlikely).
-----------------------------------------------------------------
gopher://quux.org/ conversion by John Goerzen <
[email protected]>
of
http://communication.ucsd.edu/A-News/
This Usenet Oldnews Archive
article may be copied and distributed freely, provided:
1. There is no money collected for the text(s) of the articles.
2. The following notice remains appended to each copy:
The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996
Bruce Jones, Henry Spencer, David Wiseman.
