Nautel NX15, Operation And Maintenance Manual

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NX15/NX25 Operations and Maintenance Manual Operating the transmitter
Issue 6.0 2019-01-31 Page 2-37
Figure 2.22: Signal Constellation
Signal constellation.
See Figure 2.22 . In IBOC mode only, the exciter constantly measures
the transmitter signal and performs basic demodulation of the digital carriers. The
Signal
Constellation
panel displays the phase and amplitude of the symbols being modulated within
an OFDM sub-carrier as dots on a cartesian graph. There are separate screens for each sub-
carrier. You can select sub-carriers by pressing on the carrier representation in the
SubCarrier
Group MER Spectrum
chart, or by selecting the desired subcarrier from the
SubCarrier Group
Details
list. Typically, the dots will be grouped together around the ideal data points.
Sub-carrier group information is shown in the lower, right section of the screen. Displayed
information includes the sub-carrier group name, the bandwidth that the selected carrier group
occupies and the modulation error ratio (MER) for the selected carrier group. MER quantifies
the performance of the transmitted digital signal as the ratio between the RMS power of the
ideal signal and the RMS power of the received signal’s error vector. A higher MER value is
characteristic of a smaller error, and therefore a higher quality signal. The MER out of the
transmitter is typically better than 20 dB, but can be significantly affected by external
influences such as antenna impedance and bandwidth.
NOTE:
When subcarriers are turned off in the Exgine settings, they will still appear in this
screen, but the MER will be very high (i.e., 0 to 10 dB).
Use the up or down button to maximize (if it was minimized) or minimize (if it was
maximized) the panel size.