[GreenKeys] Hal ST-6 using it in modern times

[Jim Haynes]

On Sun, 22 Mar 2020, Harold Hallikainen wrote:
>
> I remember LSMFT also. I added FSK circuitry to my Viking Ranger 50 years
> ago. And, since we generally run LSB on 80 and 40 meters, the receiver
> flipped the frequencies giving a high space on AFSK.
>
The earliest amateur RTTY was done at VHF using AFSK, and there the mark
tone is the lower of the two.  So terminal units (demodulators) were 
designed for mark low.  But when FSK was allowed at HF the standard there
(established already by non-amateur users of FSK) was low space.  So
with pre-SSB equipment you put the BFO on the high side of the carrier
frequency, which made the audio come out mark low.

Jim W6JVE