Comtech EF Data CDM-600/600L - Manual (Page 170)

CDM-600/600L Open Network Satellite Modem Revision 3
ESC++ MN/CDM600L.IOM
10–2
10.3 Available Baud Rates
At the lowest data rates, the 11.76% overhead may not allow all baud rates. The available rates
are as follows:
Data Rate Baud Rate Available
64 to 127.999 kbps 1200, 2400, 4800
128 to 191.999 kbps 1200 to 9600
192 to 255.999 kbps 1200 to 14400
256 to 383.999 kbps 1200 to 19200
384 to 511.999 kbps 1200 to 28800
512 kbps and above 1200 to 38400
10.4 Configuration
To use this mode, the user should select ESC++ from the CONFIG: MODE menu. The baud
rate and async character format are then selected from the CONFIG: MISC Æ HIGH-RATE-
ESC menu. See Chapter 5. FRONT PANEL OPERATION for further information.
10.5 Effect on Eb/No performance
Because, particularly at lower data rates, where the percentage overhead is large, the increase in
transmitted data rate will cause a decrease in the E
b
/N
o
performance. Therefore, all of the
published data concerning BER versus E
b
/N
o
needs to be modified as follows:
Data Rate Overhead ratio (percentage) E
b
/N
o
Degradation
64 kbps to < 768 kbps 19/17 (11.76%) 0.48 dB
768 kbps to 1.5 Mbps 12/11 (9.09%) 0.38 dB
> 1.5 Mbps to 2.5 Mbps 29/27 (7.4%) 0.31 dB
> 2.5 Mbps to 7 Mbps 19/18 (5.56%) 0.23 dB
> 7 Mbps 64/63 (1.58%) 0.07 dB
The degradation is simply 10 * log (Overhead ratio)
The E
b
/N
o
displayed by the modem (MONITOR: RX-PARAMS) takes this into account in the
value that is calculated.