[TenTec] Help with FSK with an Orion II

[k2ep]

I am trying to use my O2 on fsk.  Unfortunately the manual gives very little info. on this mode.  When receiving in fsk mode I must adjust my pbt to about -1800 to get readable signal.  It decodes fine then.  Is this normal?  Is there some where I can get more info. on operating fsk?  The keying sound ok on the monitor.  Mark is set low.  Are their any other setting I need to check?  I'm using a Rigblaster Advantage and mmtty s/w.  Any help would be appreciated.

Tnx,  Ernie K2EP