SLM-3650 Satellite Modem
Revision 3
Operation
MN/SLM3650.IOM
3–14
IF LOOPBACK
(Test Mode Configuration)
Programs the modem for IF loopback operation.
When IF loopback is turned ON, the demodulator input is connected to the modulator output
through an internal attenuator. 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 the previous frequency and is reconnected to the IF input.
Refer to Figure 3-24 for a block diagram of IF loopback operation.
Note: IF loopback nullifies RF loopback.
Upon entry, the current status of IF loopback is displayed. Press [
↑
] or [
↓
] to make the selection.
Press [ENTER] to execute the change.
BER THRESHOLD
Sets the BER threshold.
If the BER threshold set is exceeded, a receive fault will be indicated by the modem status
indicators. BER threshold may be set from
1.0 E-3 to 1.0 E-8, or may be disabled by specifying NONE.
Upon 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. 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.
The sweep center frequency can be set in the range from:
-35000 to +35000 Hz.
Upon 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 or
decrement the digit at the flashing cursor. Press [ENTER] to execute the change.
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. The smaller the range, the faster the modem will lock, provided the
receive carrier center frequency is within the RX IF frequency sweep range.
Upon entry, the current programmed setting is displayed. Press [
←
] or [
→
] to move the flashing
cursor. Press [
↑
] or [
↓
] to increment or decrement the digit at the flashing cursor. Press [ENTER]
to execute the change.
REACQUISITION
Programs the sweep reacquisition mode time duration. This is the time that the modem will remain
in a narrow sweep after loss of acquisition. After this timer runs out, the modem will return to the
normal acquisition sweep. The reacquisition time is 0 to 999 seconds.
Upon 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 or
decrement the digit at the flashing cursor. Select the number of seconds desired for the
reacquisition mode. Press [ENTER] to execute the change.
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