Appendix E. Eb/No Measurement - Comtech EF Data CDM-710 Installation And Operation Manual

Although the CDM-710 and CDM-710L Broadcast Satellite Modems calculate and
display the value of Rx Eb/No on the front panel 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 (i.e., Carrier density +
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 0.2dB.
• 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.
Note that the accuracy of this method degrades significantly at low values of
(Co+No)/No (approximately less than 6 dB).
Appendix E. Eb/No
MEASUREMENT
E–1