In article ,
wrote:
I guess I have bored everyone to tears by this point, but I finally
got an answer to a question that has bothered me for years:"Why did
the FCC chose the levels
specified in "Class A" and "Class B" digital devices?".

After several fruitless attempts at getting a straight answer from the
FCC, I lucked out. I met an retired engineer and he cited a "CBEMA
Study 2" that specified the lowest useful field was 48dBuV/M.

You'll have to go back to before 1983(?) when they did the "Subpart J"
regulations that defined A and B. (Those later got blended into the
Part 15 regs when they did a total rewrite in 1989).

Ah, the good old days. A co-worker of mine had a glass tty video terminal
that not only used TV scan rates, it would display a usable picture on
top of Channel 4, if properly synced. (The Van Eck paper says that some
of the old terminals could be remotely read 1/2 mile away). People who
had video games (pong type, back then) and pre-IBM personal computers
and an RF modulator would just hook them up in parallel with their
TV antenna on the back of the set, broadcasting to the neighborhood.
One notorious arcade game in a pizza parlor (described in the magazine
articles about the problem) shut down the police radio system in one
California(?) suburb. And the FAA wasn't too happy either. For an
interesting comparison compare the packaging of the Apple II (pre-Subpart
J) and the Apple III (designed after).

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)