Comtech EF Data SDM-309B - Manual (Page 147)

Maintenance SDM-309B Satellite Modem
6-6–2 MN/U-SDM309B Rev. #
an Eb/N0 of 7.5 dB. (S+N)/N is measured by taking the average level of the noise and
the average level of the top of the modem spectrum as shown. Use this measurement for
the first column on Table 6-1. Read across the page to find the S/N and Eb/N0 for the
specific code rate. Once the demodulator has locked to the incoming signal the
“MONITOR” menu will display signal level, raw BER, corrected BER, and Eb/N0
(Sections 3.1.5. and 3.2.4). These functions are not displayed until the demodulator is
locked to a carrier. A typical eye pattern with noise and without noise is shown in Figure
6-3 and a typical constellation with noise and without noise is shown in Figure 6-4. If the
demodulator does not lock up refer to the fault isolation in Section 6.2.2 to help find the
problem.