1964 Antique MODEM Live Demo

Eric Smith eric at brouhaha.com
Thu May 28 19:16:39 CDT 2009

Fred wrote:

> We saw him dial, and put the handset into the cradle, but he did NOT
> shut the lid.  The notch is there for a reason.  If you don't close
> the lid, ambient noise, such as a nearby printer or 026, can be a
> problem.
Chuck wrote:
> Yeah Fred, but a modern laptop isn't nearly as noisy as an ASR33!  I 
> don't recall Silent 700 terminals having any such lid on the acoustic 
> coupler.
Many ASR33s were equipped with an acoustic coupler to the right of the 
keyboard and printer, and they didn't have any cover to exclude outside 
noise.  They worked fine even though the ASR33 itself was quite noisy, 
because 103 FSK modulation at 110 baud [*] had a lot of noise margin.


[*]  These were actually 110 baud, since there was a one-to-one mapping 
of bits to modulation symbols.  Later modems were often incorrectly 
described as 1200 baud, 2400 baud, 9600 baud, etc., when in fact the 
quoted number was their data transfer rate in bits per second, and the 
baud rate was a fraction of that.

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