Comtech EF Data CDM-570A - Manual (Page 161)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Front Panel Operation Revision 2
6–57
For fine adjustment of the Internal 10 MHz reference oscillator, use the ▲▼arrow keys to edit
the value. The valid range of values is from –999 to +999.
1) In order to facilitate adjustment, the value updates in real time as the digits
increment/decrement. You do not need to Press the ENTER key.
2) 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:
• the internal 10 MHz reference, if you have internal access to the equipment,
or
• the Tx Output, set for CW, 0 dBm output level, and an exact center
frequency (e.g., 1000 MHz).
6.3.7.3.2 (Internal Freq Ref:) Warm-up Delay
Warm-up delay: Disable
Enable (◄ ►,ENTER)
Because the modem uses a high-stability oven-controlled 10 MHz reference oscillator (OCXO), the
modem requires a finite time period 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 settles to its correct value. This affects 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 you use the 10 MHz
reference signal 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 suspends normal operation of the modem until the operating temperature
of the OCXO stabilizes.
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 you have powered down the modem 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 achieved ambient temperature, and the external temperature is at the lowest
value possible. Under such conditions, the modem will take 2 minutes to warm-up.
If the external temperature is hot, and you power down the modem only to power up again a
short time later, the warm-up period is very short, perhaps only several seconds.