Paradise P300 Reference as backup in order to maintain the Rx traffic, Station, Same rate

	reference in order to maintain the Rx traffic. If the modem is operating with
	asymmetric data rates, then the Rx PLL converts the Tx clock to the correct rate
	for the Rx data. Should the Tx clock input fail the PLL switches to the internal
	reference as backup in order to maintain the Rx traffic.
INTERNAL	The internal 1PPM frequency reference is used to source the clock towards the
	terrestrial. Again the buffer should be set large enough to accommodate the
	difference between the internal reference and the incoming satellite clock, PLUS
	the Doppler shift whilst providing the required interval between slips.
STATION	If the Station Clock is the same frequency as the Rx data rate, then the
	Station Clock is used directly, switching to the Satellite Clock (whilst the demod
	is locked), and finally the internal reference for backups. If the Station Clock is
	at a different frequency to the Rx Data rate the Rx PLL converts the Station
	Clock to the correct rate to drive the Rx data towards the terrestrial. Should the
	Station Clock fail then the modem will switch to the internal frequency reference
	in order to maintain the Rx traffic. Again the buffer should be set large enough to
	accommodate the difference between the Station Clock and the incoming satellite
	clock, PLUS the Doppler shift, whilst providing the required interval between slips.
	Note: If the Rx is set to Station Clock AND the Tx Clocking is set to Rx ref(Stn),
	then it always operates as defined in the para above for the case where the
	“Station Clock is at a different frequency to the Rx Data rate” (even if the are the
	same rate).
DCE CLK	This option is only available if a DTE card is fitted to the modem. The DTE card
	`Ext Tx Clock In`, ie the clock from the DCE (see interface card details in
	appendix A for line names for other interfaces) is used directly as the Rx output
	clock, should the `Ext Tx Clock In` fail the PLL sources the clock, locked first to
	the Station Clock (if available) or the recovered satellite clock (while the
	demodulator remains locked), and finally the internal frequency reference in order
	to maintain the Rx traffic.

P300H P300 Series Modem Installation and Operating Handbook Page 91