CDM-625 Advanced Satellite Modem
Revision 1
Front Panel Operation
MN-0000036 (Ref MN/CDM625.IOM)
5.4.4
CONFIG: Rx
RxIF Freq FEC Demod Data Descram Eq EbNo
(Data 02048.000kbps,02184.533ksym) (
34v
)
Select the parameter on the top line using the
◄
►
arrow keys – the submenu branches available
are
RxIF
,
Freq
,
FEC
,
Demod
,
Data
,
Descrambler
,
Eq
, and
EbNo –
then press
ENTER
.
Observe the Data/Symbol rate information on the bottom line.
5.4.4.1
CONFIG: Rx
Æ
Rx-IF
Acquisition Sweep Range = +/- 032 kHz
Spectrum Invert=Off (Off,On)
(
34v
)
Two Rx parameters may be edited in this menu. Select the parameter to edit using the
◄
►
arrow keys. The available options are shown in parentheses. Use the
▲
▼
arrow keys to edit the
setting, then press
ENTER
when done.
The 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:
Sweep Range Limit
Rx Symbol Rate
13-32 kbps
+/-1 to symbol rate
32- 389 ksps
+/-1 to 32 kHz
389-2000 ksps
+/-1 to (10% of symbol rate)
>2000ksps
+/-1 to 200 kHz
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.
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