88-ACR KCS modification

Grant Stockly grant at stockly.com
Tue Dec 26 17:28:37 CST 2006


>Not possible.  The ACR is simple FSK and the KCS is redundent FM.

What is redundant FM?  The wiki article I found described it as being 
AFSK.  2400Hz for a 1 and 1200Hz for a 0.

http://en.wikipedia.org/wiki/Kansas_City_standard

I was given a document (from Tom Sanderson) that described a "New Audio 
Modulation Method for ACR".  From the Computer Notes Feb. 1976.

It does not mention the KCS, but it does raise 1 from 2225Hz to 2400Hz, and 
lower 0 from 2025Hz to 1850Hz.

The document mentions that because the center frequency hasn't changed that 
a tape recorded with 2225/2025 can still be read.  I assume that the lower 
frequency could be dropped further to 1200Hz, but then maybe it becomes 
incompatible with older tapes?


>As to the latter question of component use... the ACR was intended as a
>modem (bell 103) and it's design was based on that.

My question was why did MITS not use the modulator built into the XR-210.

What's the deal with cctech and cctalk?  Why do some messages go to 
both?  Why do replies to some messages from cctalk go to cctech?  Does the 
moderator decide which cctalk messages go to cctech?

I'm a little confused...

Thanks,
Grant




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