Wavecom W61PC V7.5.0 - Manual (Page 83)

WAVECOM Decoder W61PC/LAN Manual V7.5 Analysis Tools  73
FSK Analysis
The FSK analysis mode is an important tool to measure the baud rate and frequency shift of FSK transmis-
sions. The magnitude of these property values may help to identify the transmission being monitored.
To open the FSK analysis window go to the HF-Modes menu and select Analysis/FSK Analysis, or use
the FSK Analysis button. The baud rate and spectrum window will open, but NOT the waterfall window.
After a few seconds the baud rate and spectrum window are updated.
The FSK analysis window consists of four panes:
 A spectrum graph pane
 A spectrum waterfall pane
 A baudrate graph pane
 A baudrate waterfall pane
Baudrate and Spectrum Window
The baudrate and spectrum window are two-dimensional displays of the monitored baud rate, measured in
Baud, and the spectrum of the transmission, measured in Hz, on a relative scale from 0 to 100. The dis-
plays are updated around every 5 seconds. The calculated baud rate, center frequency and frequency shift
values of the latest sample are stored to be used whenever a decoding mode is selected.
Two pairs of cursors may be placed in the baudrate and spectrum graph windows, to assist in manual
measurements. The values to which they point, and the difference between the two cursor values, are
shown above the cursors. When a pair of cursors is placed in one of these windows, graph display updat-
ing is halted, but signal sampling continues and is displayed in the waterfall window. The time cursor in
the waterfall window is placed on the selected sample.
Methods exclusively based on bit length measurement are unreliable for baud rate measurements. The
baud rate measuring process employed by the decoder is therefore based on a new method employing au-
to-correlation and subsequent Fast Fourier Transformation (FFT) presentation. Using this method, FSK
transmissions may be analyzed without problems. Be aware that when measuring the baud rate of codes
using code words which have a non-integer number of bits, e.g. asynchronous 7.5-bit ITA-2, the indicated
baud rate will increase by a factor two.