Comtech EF Data CDM-625A - Manual (Page 648)

CDM-625A Advanced Satellite Modem MN-CDM625A
Appendix J Revision 3
J–2
J.3 Available Baud Rates
At the lowest data rates, the 11.76% overhead may not allow all baud rates. Available rates
are as follows:
Data rate Baud rates 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
J.4 Configuration
Chapter 6. FRONT PANEL OPERATION
Use the SELECT: Configure  Mode menu to select ESC++. Then, use the SELECT: Configure 
Misc  HiRateESC menu select the baud rate and asynchronous character format.
J.5 Effect on Eb/No Performance
Because the increase in transmitted data rate will cause a decrease in the Eb/No performance –
particularly at lower data rates where the percentage overhead is large – all of the published
data concerning BER versus Eb/No needs to be modified according to the table that follows:
Data rate Overhead ratio (percentage) Eb/No 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 x log (Overhead ratio).
The Eb/No displayed by the modem (SELECT: Monitor RX-Params) takes this into account in
the value that is calculated.