Path: utzoo!utgpu!water!watmath!clyde!bellcore!faline!thumper!ulysses!andante!mit-eddie!ll-xn!oberon!sdcrdcf!trwrb!trwind!johng
From: johng@trwind.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: 9600 baud over high-quality audio channel
Keywords: modem
Message-ID: <403@trwind.UUCP>
Date: 29 Jun 88 16:17:29 GMT
References: <17507@glacier.STANFORD.EDU> <5063@videovax.Tek.COM> <189@cbw1.UUCP>
Reply-To: johng@trwind.UUCP (John Greene)
Organization: TRW Information Networks Div
Lines: 34

In article <189@cbw1.UUCP> brian@cbw1.UMD.EDU (Brian Cuthie) writes:
>In article <5063@videovax.Tek.COM> bill@videovax.Tek.COM (William K. McFadden) writes:
>>
>>>     I'd like to transmit 9600 baud, simplex, (one-way) over a good-quality
>>>audio channel that can handle at least 10KHz.
>>
>>This might seem too obvious, but why not connect the output of your RS-232 port
>>directly to the input of your audio channel (using suitable attenuation and DC
>>blocking)?  At the receive end you would probably want some sort of active
>>filtering and schmitt triggering to recover the data.  The problems I could
>
>The first problem I see with this is that the audio path is not DC coupled
>and thus you would have big problems with data that was all marking.  Now if
>you MFM encoded the data you might get by, but I doubt it.  This is why
>people invented modems for phone lines (audio channels -- right ?).
>

This type of thing has been done before by Standard Microsystems Corporation
(SMC) with their ARCNET chipset.  Data Rates of up to 2.5 MegaBits/sec have
been acheived on standard phone line.  The Network driver IC (COM9032 I think)
is rather extpensive (~$30) but the concept it operates on can be done 
descreetly for little money.  It transmits a 'dipulse' for a logical 1 and
nothing for a zero.  Since RS232 characters are framed with a start and stop
bit, it should not require anything special to reconstuct the signals.  The
data book is pretty decriptive on how it works and I think that it even has
a partial schematic of what is inside of the chip.  

Hope this helps.

-- 
John E. Greene    "People are just like frankfurters....You have to decide
                   if you're going to be a hot dog or just another wiener" DLR
TRW Information Networks Division 23800 Hawthorne Blvd, Torrance CA 90505
ARPA: johng@trwind.ind.TRW.COM  USENET: ..trwrb!trwind!johng