Comtech EF Data CDM-570 - Manual (Page 133)

CDM-570/570L Satellite Modem with Optional IP Module Revision 12
Front Panel Operation MN/CDM570L.IOM
5–47
5.2.2.6.4 UTIL: Ref Æ Adjust
Internal 10 MHz Freq Ref
Fine Adjust:+017(◄ ►,▲ ▼)
This menu permits fine adjustment of the Internal 10 MHz reference oscillator. Use the
▲ ▼
arrow keys to edit the value. The range of values is from –999 to +999.
Note: In order to facilitate adjustment, the value updates in real time as the digits are
incremented/decremented. You do not need to press the ENTER key.
Note: The numbers displayed here do not correspond to an exact frequency increment. You
should perform this fine adjustment while using an external frequency counter, connected either
for:
a) the internal 10 MHz reference, if you have internal access to the equipment, or
b) the Tx Output, set for CW, 0 dBm output level, and an exact center frequency (e.g., 1000
MHz).
5.2.2.6.5 UTIL: Ref Æ Warm-up Delay
Warm-up delay: Disable
Enable (◄ ►,ENTER)
Because the CDM-570/570L uses a high-stability oven-controlled 10 MHz reference oscillator
(OCXO), a finite time period is required for the oven to reach operating temperature. Consequently,
when the modem first powers up a frequency error as great as 2 x 10
-6 will occur, and it may take up
to 2 minutes before the frequency has settled to its correct value. This will affect the Tx synthesizer
(and hence the Tx output frequency), the Rx synthesizers, and the generation of the Internal Tx
baseband clock.
For a modem operating on its own, this may not be a problem, but if the 10 MHz reference signal is
being used to drive an externally-connected BUC, the frequency error at the RF output may be
large, particularly at Ku- or Ka-Band.
In order to avoid this problem, you may choose to enable a warm-up delay, which will suspend
normal operation of the modem until the operating temperature of the OCXO has stabilized.
Warm-up delay is not fixed. Instead, the modem uses an intelligent algorithm to minimize this
delay, under all circumstances. The modem uses its internal temperature sensor, and knowledge of
how long the modem has been powered down, to determine the duration of the warm-up delay
period.
For example: The worst case occurs when the modem has been powered down sufficiently long
that the modem has reached thermal equilibrium with its surroundings, and the external temperature
is at the lowest value possible. In this circumstance the modem will take 2 minutes to warm-up.
If the external temperature is hot, and the modem was powered down and then powered up again a
short time later, the warm-up period will be very short, perhaps only several seconds.