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PHASE ERROR (DEGREES) | Up
Fire Controlman Volume 06-Digital Communications | Next
RECOGNIZING LINK-11 NET PROBLEMS |
Figure 3-13.—The Spectrum Display screen of the LMS-11.
are the odd harmonics of 55 Hertz. The spectrum
MISSED CODES %.— This is a percentage of
each type of code that is missed. The number of
codes (start, stop, and address call-ups) missed and
received is tabulated and the percentage of each type
missed is calculated.
FRAMES.— This is the total number of data
frames received, including the phase reference and
control code frames.
CS.— This field displays the carrier suppression
value of the upper and lower sidebands as a ratio of
the power in the 605-Hz tone to the power of the
carrier frequency. The value display is measured in
dB .
RFE/DS.— The radio frequency error or Doppler
shift of the received signal in Hertz. The display is
color-coded cyan if frequency correction was disabled
during LMS-11 initialization.
Spectrum Display
The spectrum display graphically shows the power
levels of all the Link-11 tones and the noise tones that
display screen is shown in figure 3-13. The x-axis of
the bar graph is numbered from 1 to 30 to represent 30
tones. Tone 05 is the 605-Hz Doppler tone. Tones 8
through 21 and tone 26 are the data tones. The
remaining tones are not used by the Link-11 system
but are sampled and displayed to give the operator an
indication of the noise level.
The y-axis of the bar graph displays the relative
power of each tone in dB. The highest value of the
scale is 0 dB and decreases to -40 dB. The tone with
the greatest amount of power is set to 0 dB on the
scale.
This should be the 605-Hz tone. The
remaining tones are measured relative to the tone with
the greatest power.
A single blue line is drawn
horizontally across the screen at the -6 dB level.
Ideally, all data tones should extend up to this line.
The 605-Hz tone and the data tones are displayed
by solid green vertical lines. If the power of a data
tone is greater than -6 dB with respect to the 605-Hz
tone, the area above the -6 dB line is indicated by an
open yellow bar on top of the green bar. If the power
level of a data tone is below the -6 dB threshold, an
open yellow bar is used to fill in the remaining
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