[GreenKeys] HAL ST-6 - squelch?

[Duncan Brown]

The Introduction to the ST-6 manual states: "An automatic control holds 
the ST-6 in the mark condition when non-RTTY signals (such as voice, cw, 
or noise) are received."

When monitoring ham RTTY/RATT QSOs, I get a lot of random characters 
printed (from noise) between transmissions, so I don't seem to have (or 
have working) the "squelch" function mentioned above.  I also don't see 
anything in the schematics that might be doing this function.

Am I missing something?  Does the ST-6 have a "squelch" function? If so, 
where?

Thanks & have fun,

Duncan
K2OEQ