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SDM-309B Satellite Modem
IFLoopBk
RFLoopBk
SWP_RACQ
**SWP_CNTR
**SWP_RNGE
MN/U-SDM309B Rev. #
*Programs the modem for IF loopback operation. When the IF loopback
is turned on the demodulator input is connected to the modulator output
through an 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
turned to it's previous frequency and is reconnected to the IF input. See
Figure 3-8 for a block diagram of IF loopback operation.
On entry the current status of the IF loopback is displayed with a flashing
cursor on the first character. Use the arrow keys to select ON or OFF.
Press the "ENTER" key to execute the change.
*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 loop-back is turned off the demodulator is tuned to
it's previous frequency. See Figure 3-9 for a block diagram of RF
loopback operation.
On entry the current status of the RF Loopback is displayed with the
flashing cursor on the first character. Use the arrow keys to select ON or
OFF. Press the "ENTER" key to execute the change.
This function sets the sweep reacquisition rate from 0 to 999 seconds.
The time selected with this parameter is the time that the modem will
remain in a narrow sweep (± 10%) after acquisition has been
accomplished. After this timer runs out the modem will return to the
normal sweep.
On entry the current programmed setting is displayed with a flashing
cursor on the first character. Use the right and left arrow keys to move
the flashing cursor and the up and down arrow keys to increment and
decrement the digit at the flashing cursor. Select the number of seconds
for the reacquisition mode form 0 to 999 seconds. Press the "ENTER"
key to execute the change.
Programs the sweep center frequency for the directed sweep function.
The sweep center frequency may be set in the range from +25000Hz to -
25000Hz.
On entry the current programmed setting is displayed with a flashing
cursor on the first character. Use the right and left arrow keys to move
the flashing cursor and the up and down arrow keys to increment and
decrement the digit at the flashing cursor. Select the sweepcenter
frequency from -25000Hz to +25000Hz. Press the "ENTER" key 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.
Programs the overall travel of the sweep width range during acquisition in
the directed sweep mode. The sweep width may be set from 0 Hz to
50000 Hz. (When set at 50000 Hz, the modem is in the fast acquisition
mode).
On entry the current programmed setting is displayed with a flashing
cursor on the first character. Use the right and left arrow keys to move
the flashing cursor and the up and down arrow keys to increment and
decrement the digit at the flashing cursor. Select a sweep range from 0
Hz to 50000 Hz. Press the "ENTER" key to execute the change.
When in directed sweep, the smaller the range is, the faster the modem
will lock, provided the sweep center frequency is close.
Operation
3–29
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