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•
Advanced Topics
WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
Try and view the phase plane of the signal using the
SYNC Mode
, using the DPSK
demodulator. If the signal is a PSK signal, the phase plane should be visible.
If the
SYNC Mode
failed to produce a meaningful display, try the
ASYNC Mode
. This
requires accurate adjustment of the Reference signal to produce a meaningful display. The
ASYNC Mode
will also produce a useful display for many PAM signals.
MFSK ANALYSIS
The MFSK analysis for the HF range employs a graphical display in two dimensions,
frequency (y axis) and time (x axis). Both values may be preset. This tool was originally
developed for the analysis of analogue tone call systems, but is equally suitable for evaluation
of FSK and MFSK systems. In particular the frequency and element duration is well displayed.
After starting "
MFSK Analysis
" the detected frequency values are displayed as pixels.
A monitored MFSK signal is easily recognized as stable lines. To
stop
the horizontally
scrolling display click on the display.
Measurement cursors
for both the time axis and the
frequency axis appear. The display may be searched to the maximum extent of 15 seconds
when tracking rate is set to 1 ms. However, if tracking rate is set to 15 ms a range of 225
seconds may be searched.
"
Tracking rate
" determines the sampling rate. The range is 1 - 15 ms, default is 2 ms.
Double-clicking "
Filter
" inserts a low pass filter for filtering the selcal system tones. The
value of the filter should be adjusted to avoid serious tone distortion. A rule-of-thumb value is
1.6 times the baudrate. The actual value may be calculated so:
•
tfilter [ms] = (2*1000)/(Baudrate*1.6)
The filter range is 1 - 100 ms.
Using the "
Span
" menu the resolution of the frequency axis may be increased. The steps are
3,000 Hz (analogue selcal systems), 1,500, 600 and 300 Hz.
From the "
Center
" menu the center frequency may be adjusted. It is important to readjust the
center frequency whenever the frequency ("Span") axis is increased.
Several
color schemes
are available through the right-click menu.
Summary of Contents for W40PC
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Page 56: ...48 General Operating Procedure WAVECOM Decoders v6 15 W40PC W41PC W51PC...
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