Comtech EF Data CDM-600/600L - Manual (Page 39)

CDM-600/600L Open Network Satellite Modem Revision 3
Introduction MN/CDM600L.IOM
1–11
o
Second, the High Rate (2nd Generation) TPC option provides data rate capability up
to 20 Mbps, in addition to Rate 7/8 and Rate 0.95 capability.
o
Third, the combination Low-density Parity Check (LDPC) and TPC Codec is capable
of data rates up to 20 Mbps, and provides Rate 1/2, Rate 2/3 and Rate 3/4 code rates
across the range of modulation types.
• The fourth hardware option is the Internal/External High Stability Reference. It provides a
frequency stability of 2 x 10
-8
. This may be fitted in the factory at the time of order, or
fitted in the field as an upgrade (provided the CDM-600 was manufactured after a certain
date - consult the factory for further information).
This option provides an additional connector on the rear panel to permit the connection of a
high-stability external reference signal, which in turn will phase-lock all of the internal
frequency generation circuits of the CDM-600, including the IF synthesizers. The new
connector is an SMA female type, located at the extreme right of the rear panel (when
looking at the rear panel). This connector accepts signals at 1, 2, 5, 10 or 20MHz, over the
range -5 dBm to +15 dBm, and is matched for both 50 and 75
Ω systems.
The frequency is selected from either the front panel or over the remote control interface.
If the user selects external reference operation, the unit expects to see an appropriate signal
at this connector. If the monitor circuit does not sense a signal at the connector, a Traffic
Alarm is generated, and the High-Stability Internal Reference (stability of 5 x 10
-8 ) is
automatically substituted.
If the user selects Internal Reference, the user may then adjust the exact frequency of the
reference using the front panel, or the remote control interface.
In External mode, the High-Stability Internal/External Reference Module works by phase-
locking the Internal Reference to the externally applied signal. If for some reason (perhaps
an incorrect frequency being applied) the PLL circuit senses a loss of lock, a Unit Alarm is
generated, and the TX carrier will be muted.
Because the High-Stability Internal Reference is comprised of an Ovenized Crystal
Oscillator (OCXO) there is a warm up period associated with this scheme. The user may
select, either from the front panel or via the remote control, to have the unit:
o
Power-up instantly (in which case the frequency of the unit will drift until the oven
has reached its correct operating temperature),
OR:
o
Select a warm-up delay, where the unit will not become operational until the oven
has reached a temperature close to stabilization value.
CDM-600 Hardware Option Notes:
1. The CDM-600 uses an intelligent algorithm that takes into account the internal
temperature of the unit, and the amount of time it has been powered down. In this way,
the unit does not wait for the full period (which can be as much as 200 seconds) if
power is cycled over a short time.
2. If the warm-up feature has been activated, the time-out period can be instantly
terminated by pressing [CLR] on the front panel keypad.