Comtech EF Data CDM-625 - Manual (Page 121)

CDM-625 Advanced Satellite Modem Revision 15
Front Panel Operation MN-CDM625
5–21
5.2.1.4 CONFIG: Rx
RxIF Freq FEC Demod Data Descram Eq EbNo
(Data 02048.000kbps,02184.533ksps) ()
On the top line – Use the ◄ ► arrow keys to select RxIF, Freq, FEC, Demod, Data (Symb when in
IP-ACM Mode), Descram, Eq, or EbNo, and then press ENTER.
On the bottom line – Read-only Data/Symbol rate information is provided.
When Sub-Mux is ON, the Data Rate information on the bottom line of this display
is replaced by Composite Rate information.
5.2.1.4.1 CONFIG: Rx  Rx-IF
Acquisition Sweep Range = +/- 032 kHz
Spectrum Invert=Off (Off,On) ()
Use the ◄ ► arrow keys to select Acquisition Sweep Range or Spectrum Invert (available
options are shown in parentheses).
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, when selecting ±32 kHz with a data rate of 2.4 kbps, BPSK will
result in an average acquisition time of around 3 minutes.
Use the ▲▼ arrow keys to edit the setting in 10 kHz increments, and then press ENTER. The Rx
symbol rate determines the Sweep Range limits:
Rx Symbol Rate Sweep Range Limit
±1 to symbol rate / 2 (ksps) 18 - 64 kbps
±1 to 32 kHz 64 - 389 ksps
±1 to (10% of symbol rate) 389 - 2000 ksps
±1 to 200 kHz >2000ksps
Use the ▲▼ arrow keys to set Spectrum Invert as Off or On, and then press ENTER.
SPECTRUM INVERT should normally be in the OFF position. When in the ON
position, the Rx spectrum is inverted (which is the same as reversing the direction
of phase rotation in the demodulator). When in BPSK mode, note that 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.