[GreenKeys] Fwd: Very Slow Shift Frequency keying?

[Harold Hallikainen]

In the 1980s, the FCC authorized data transmission by AM stations. Prior
to that, in 1967, use of subaudible tones on AM was proposed for
transmitter telemetry (
http://hallikainen.com/nab/unattended/RegHistory.pdf#page=16 ). This was
finally accepted in 1969 (
http://hallikainen.com/nab/unattended/RegHistory.pdf#page=17 ). By the
way, those links are from a book I wrote for the National Association of
Broadcasters many years ago.

By the 1980s, the FCC largely got out of defining modulation methods and,
instead, just required a station stay within a specified spectral mask. A
method of transmitting data through phase modulation of the AM carrier is
described at
https://worldradiohistory.com/Archive-NAB-Publications/NAB-Radio-Subcarrier-Services-%201983.pdf#page=15
.

All of this is a form of "data broadcasting." The FCC specifically
authorized facsimile broadcast by AM stations using a subcarrier above 20
kHz. See section 3.318 at
https://hallikainen.org/org/FCC/FccRules/1955/rules19551104.pdf#page=61 .

And, as I recall reading, there were "newspapers of the air" delivering
fax over AM broadcast stations.

Harold
https://w6iwi.org