Comtech EF Data SDM-100A - Manual (Page 48)

Operation SDM-100A Satellite Modem
3–14 Rev. 0
IF Loop Back Programs the modem for IF loopback operation (test mode).
When IF loopback is turned on, the demodulator input is connected to
the modulator output through an internal attenuator, and the
demodulator is programmed to the same frequency as the modulator.
An attenuator within the modem connects the IF out to the IF in. When
IF loopback is turned off, the demodulator is tuned to its previous
frequency, and is reconnected to the IF input. Refer to Figure 3-27 for
a block diagram of IF loopback operation.
Note: IF loopback nullifies RF loopback.
On entry, the current status of IF loopback is displayed. Press [
↑ ] or [ ↓ ]
to select ON or OFF. Press [ENTER] to execute the change.
BER Threshold This function is used to set the BER threshold.
If the set BER threshold is exceeded, a receive fault will be indicated
by the modem status indicators. BER threshold may be set from 1E
-3
to 1E -8 , or may be disabled by specifying NONE.
On entry, the current setting of the BER threshold is displayed. Press
[
↑ ] or [ ↓ ] to select the desired setting. Press [ENTER] to execute the
change.
Sweep Center Programs the sweep center frequency for the directed sweep function.
The sweep center frequency may be set in the range from -35000 to
+35000 Hz.
On entry, the current programmed setting is displayed with a flashing
cursor on the first character. Press [
← ] or [ → ] to move the flashing
cursor. Press [ ↑ ] or [ ↓ ] to increment and decrement the digit at the
flashing cursor. Select the sweep center frequency from -35000 to
+35000 Hz. Press [ENTER]
to execute the change.
When in directed sweep, the value from the sweep monitor screen
(when the modem was last locked) should be entered for the sweep
center frequency.
Sweep Range Programs the overall travel of the sweep width range during acquisition
in the directed sweep mode.
The sweep width may be set from 0 to 70000 Hz. (When set at 70000
Hz, the modem is in the normal acquisition mode.)
On entry, the current programmed setting is displayed with a flashing
cursor on the first character. Press [
← ] or [ → ] to move the flashing
cursor. Press [ ↑ ] or [ ↓ ] to increment and decrement the digit at the
flashing cursor. Select a sweep range from 0 to 70000 Hz. Press
[ENTER]
to execute the change.
Note: The smaller the range is, the faster the modem will lock,
provided the receive carrier center frequency is within the RX IF
frequency sweep range.