Table of Contents
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Operation
RF LOOP BACK
(Test Mode Configuration)
IF LOOP BACK
(Test Mode Configuration)
BER THRESHOLD
SWEEP CENTER
SWEEP RANGE
3–14
Programs the modem for RF loopback operation.
When RF loopback is turned on, the demodulator is programmed to the
same frequency as the modulator. When RF loopback is turned off, the
demodulator is tuned to the previous frequency. Refer to Figure 3-23
for a block diagram of RF loopback operation.
Note: RF loopback nullifies IF loopback.
Upon entry, the status of the RF loopback is displayed. Press [↑] or [↓]
to make the selection. Press [ENTER] to execute the change.
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 status of IF loopback is displayed. Press [↑] or [↓] to
make the selection. Press [ENTER] to execute the change.
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.
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.
Programs the travel of the sweep width range during acquisition in the
directed sweep mode. The range 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.
SDM-300A Satellite Modem
Rev. 4
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