Comtech EF Data CDD-562AL, Installation And Operation Manual

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CDD-562AL/564A/L Multi-Channel Demodulator Revision 0
Eb/N0 Measurement MN-CDD562AL564AL
B–1
Appendix B. E
b
/N
0
MEASUREMENT
Although the CDD-56xA/L demodulator calculates and makes the value of receive E
b
/N
0
available
through the remote port of the unit, it is sometimes useful to measure the value using a spectrum analyzer,
if one is available.
The idea is to accurately measure the value of (Co+No)/No, (Carrier d Noise density/Noise
density). This is accomplished by tuning the center frequency of the Spectrum analyzer to the signal of
interest, and measuring the difference between the peak spectral density of the signal (the flat part of the
spectrum shown) and the noise density.
To make this measurement:
•
Use a vertical scale of 1 or 2 dB/division.
•
Set the Resolution Bandwidth of the Spectrum Analyzer to < 20% of the symbol rate.
•
Use video filtering and/or video averaging to reduce the variance in the displayed trace to a low
enough level that the difference can be measured to within 0.2 dB.
•
Place a marker on the flat part of the signal of interest, then use the MARKER DELTA function
to put a second marker on the noise to the side of the carrier. This value is (Co+No)/No, in dB.
•
Use this value of (Co+No)/No in the table on the following page to determine the Eb/No. You
will need to know the operating mode to read from the appropriate column.
•
If the (Co+No)/No value measured does not correspond to an exact table entry, interpolate using
the two nearest values.
The accuracy of this method degrades significantly at low values of (Co+No)/No (approximately less
than 6 dB).