On 18 Jan 2007 00:59:17 -0800, "tom k in L.A."
wrote:

what is all this "PSHHHHHT" [pause] "PSHHHHT" [pause] "PSHHHT"
[pause] I hear on some shortwave freqs?

Give us a better clue - post the actual frequencies, so we can listen
to it, too.

Right off the top of my head though, your description brings to mind
ANDVT (Advanced Narrowband Digital Voice Terminal), but it's hard to
come up with a definitive mode ID without listening to a signal.

John Kasupski, KC2HMZ