Comtech EF Data CDM-600/600L - Manual (Page 91)

CDM-600/600L Open Network Satellite Modem Revision 3
Front Panel Operation MN/CDM600L.IOM
5–15
5.4.4.1 CONFIG: RX
Æ RX-IF
ACQUISITION SWEEP RANGE = +/- 10 kHz
RX FREQ=1200.0000MHz SPECTRUM INVERT=OFF
Select the parameter to edit – the Acquisition Sweep Range, RX Freq, or SPECTRUM
INVERT – using the [
←][→] arrow keys.
The Acquisition Sweep Range value determines the amount of frequency uncertainty the
demodulator will sweep over in order to find and lock to an incoming carrier. When operating at
low bit rates, large values of sweep range (compared to the data rate) cause excessively long
acquisition times.
For example: Selecting
± 32 kHz with a data rate of 2.4 kbps, BPSK will result in an average
acquisition time of around 3 minutes.
The Sweep Range limits are determined by the Rx symbol rate. To edit the Acquisition Sweep
Range of the demodulator, change the value of the digit using the [
↑][↓] arrow keys, then press
[ENT] when done.
Edit the Rx Frequency by selecting each digit to be edited using the [ ←][→] arrow keys, then
edit the value of the digit using the [ ↑][↓] arrow keys. When editing is complete, press [ENT].
For the CDM-600L: Note that the range is from 950-1950 MHz.
For the CDM-600: Note that the range is from 52-88 MHz, and 104-176 MHz. The resolution is
100Hz. For units manufactured after February 2005 that display CDM-600(E) on the opening
menu, the range of IF frequencies has been extended to 50-90 MHz, and 100-180 MHz.
To set the Rx spectrum inversion, set SPECTRUM INVERT to OFF or ON using the [ ↑][↓]
arrow keys. Press [ENT] when done.
IMPORTANT
SPECTRUM INVERT should normally be in the OFF position. When in the ON
position, the receive spectrum is inverted (which is the same as reversing the
direction of phase rotation in the demodulator). Note that in BPSK mode, the
demodulator will automatically synchronize to either the normal time-ordering
of bits FEC codeword pairs, or the inverted ordering used by certain other
manufacturers.