Freedom R8100 SERIES, Руководство оператора

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Figure 2.2.7.7-6. Mod Spec / Constellation (Symbols)
Mod Spec / Constellation
Modulation Spectrum display
Displays the power versus frequency (power spectral density) of the modulated symbols in the detected
burst. Power is shown in dB relative to Input Level (0 dB); frequency is shown in kHz relative to Center
Frequency (0 Hz). The measurement is done by over-sampling at the optimal symbol times and positions
to exclude adverse effects of frequency error and residual carrier.
Constellation display
The Constellation display provides a visual representation of overall transmitter operation – see Figure
2.2.7.7-6. The constellation data represents just the data of the useful part of the burst. The measurement
is done at the optimal symbol times and positions to exclude adverse effects of frequency error and residual
carrier.
TETRA radios broadcast voice and data using 4 differential phase shift deviations from the carrier to
represent symbols containing 2 data bits. One of four phase shifts relative to the carrier’s current phase
yields eight phase points. The phase trajectory never passes through the origin, ensuring that signal
amplitude never falls to zero during data transmissions. See Figure 2.2.7.7-7. The center of the eight red
circles on the display represent the expected locations for the deviation states when the radio is
transmitting data bit symbols using the modulation. White dots show the actual deviation measurement at
symbol decision times. A tighter grouping within the red circles indicates more accurate transmitter
performance. The radius of the circles is the 10% EVM (Peak) limit.