I've found a control Data 8528 Digital Communications Terminal Reference
Manual at a book sale for $1 :-)
It's letter size, soft cover, about 100 pages, contains a number of
schematics and is copyrighted in 1964. The 8528 appears to be a 12-bit
modem that can be used over coax, microwave or leased telephone links at
up to 10^5 words/sec. It comes with a telephone handset in case you want
to talk to the person on the other end :-)
It can be yours for the cost of media mail shipping from 27606. I see that
CHM has one (but no scans posted), but I don't see a copy on bitsavers, so
Al gets dibs if he wants it. I can also scan it free for anyone who's
interested.
Alexey