Nautel NX5 AM, Руководство по эксплуатации и техническому обслуживанию

Страница: 62 / 220

NX5 OPERATION & MAINTENANCE MANUAL OPERATING THE TRANSMITTER
PAGE 3.2.42 VERSION 0.1 2015-08-01
Figure 3.2.30: Signal Constellation
Signal Constellation
See Figure 3.2.30 . In IBOC mode only, the exciter continuously measures the transmitter’s output 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 group as dots on a
cartesian graph. There are separate screens for each sub-carrier group. You can select sub-carrier
groups by clicking on the carrier representation in the
SubCarrier Group MER Spectrum
chart, or by
selecting the desired subcarrier group 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.
Panel shown maximized