The WiNRADiO Universal FSK Decoder is an extremely versatile
signal decoding utility for WiNRADiO receivers 1000/1500 or 3000 series,
as well as G3 series. Using WiNRADiO models with in-built DSP (for example WR-G313i) will provide the best decoding quality;
however, the Decoder will also work well with a sound card.
The Decoder contains several powerful analysis tools, making it possible to
determine transmission characteristics of an unknown signal automatically.
Looking at the decoder's main control panel on the right, you will see a drop-down list
at the top, labelled Protocol. Here you can select the type of coding protocol
used. Using the Add or Edit buttons, new protocols can be added,
either created entirely from scratch (the number of variable parameters makes the number
of usable protocols almost unlimited), or by deriving new protocols from existing
ones by modifying some of their parameters.
A "protocol" consists of all the various settings and parameters
which are needed to be able to decode a signal, including the type of coding,
mark/space frequencies, baud rate, character format, translation table, etc.
The first stage of the signal decoding chain is the level detector,
visible at top-left of the main control panel above.
This detector allows the user to determine whether an adequate audio signal level
exists at the decoder input. This facility is available
only when a sound card is used; in such case the level should be adjusted either
using the receiver or sound card volume settings. With WiNRADiO DSP receivers,
the level control is automatic.
Universal FSK Decoder - Spectrum Analyzer
Universal FSK Decoder - Spectrum Analyzer
The signal is then passed to the Spectrum Analyzer section for frequency domain analysis. The analyzer estimates
the two "mark/space" frequencies of the FSK modulation process. These are displayed in the Estimated section of the Frequencies group on the control panel. The user has a choice
either using these automatically estimated values or pre-set values which can be also
The detected frequencies are indicated by two markers. The
spectrum is simultaneously displayed as either a continuous line or bars
in the top display and as a "waterfall" in the bottom one. The
spectrum can be shown using either logarithmic or linear values.
If the mark/space frequencies are known, then manual entry is of course
also possible. These values can be also preset as part of standard, or user-defined
There is also a facility to keep the shift between mark and space frequencies
constant. The shift can be either 170Hz, 425Hz, 850Hz or a user-specified arbitrary value.
The result of the mark/space frequencies estimator, either in manual or
fully automatic mode, is then passed on to the Signal Demodulator. The Signal Demodulator module utilizes the two specified mark/space
frequencies and extracts the data signal. There are two modes
available, optimal and high speed.
Universal FSK Decoder - Demodulator
The Demodulator relies upon three input variables: the two FSK frequencies
(mark/space) and the bit length. The mark/space frequencies are used always
for the demodulation process, while the bit length is used only when the optimal
mode is active.
In order to see the signal at different processing stages, a logic
schematic of the demodulator is shown on the panel, with several test
points (the cyan points).
Click on one of the test points, and the signal at that point will be displayed
on the oscilloscope on top of the panel.
An eye pattern scope has been also implemented for the
final output and the positive input of the data formatter.
The data signal extracted by the Demodulator is then sent to two
separate processing modules.
The first is the
Time Estimations module which attempts to determine
the bit length and the baud rate. The estimated value is displayed for
reference, and it can be either used for further processing,
or ignored by the user if a manually entered or preset value is preferred.
Universal FSK Decoder - Time Estimator
Using the measured time intervals between two transitions, the Time Estimator
creates a histogram, the upper one as shown on the adjacent panel.
There are two
cursors, one corresponding to the length of single bits and the other to the
length of two-bit pairs. If one of them is being dragged, the other one
In addition to this first histogram, a second (bottom) one is generated using
autocorrelation of the time intervals. This is used for final estimations
of the bit length.
The estimated bit length parameter is used by the optimal demodulator,
while the baud rate is required for the actual character decoding.
The automatic baud rate estimation is suitable only for continuous bit
streams. Transmission modes such as Packet Radio, SITOR-A,
ARQ6-70/90/98, SWED-ARQ require the baud rate to be set manually.
Universal Decoder - Data Output Window
The Data Output window shows the result of the
entire demodulation and decoding process. It uses the data
provided by the processes described above, as well as several additional
user-adjustable parameters. Sometimes the transmitted characters are
passed through a bit inversion mask; the decoder can easily
handle this situation and special protocols can be defined when the
correct mask has been identified. Also, certain protocols
are polarity-dependent while others require automatic mode for
correct functionality. These parameters can be set on the main control panel
in the Bit Inversion Mask and Polarity groups of buttons.
Universal FSK Decoder - Character Translation Table
Before the decoded characters are displayed, they are passed through
the Translator which relies upon a set of character translation tables
to provide translation of the raw characters to national alphabets.
These tables can be selected also in the main control panel of the Decoder,
as one of the parameters which form the entire "protocol".
Each protocol is derived from five generic decoding modes: ITA2
(Baudot), IRA (ASCII), SITOR, Packet and Raw Bits. For each mode,
a different version of the Decoder section is shown on the main control panel;
the two examples shown here pertain to IRA and SITOR.
Universal FSK Decoder - Character Statistics
The "icing on the cake" of this multi-featured decoder is the Character Statistics
display which creates a character histogram of the received text.
The number of displayed bars (each corresponding to a different character) depends on the currently selected protocol.
The bars are ordered by the character hex code. The displayed information is always normalized to the largest value.
The statistics for each bar can be seen by simply moving the mouse over it.
This is a very useful facility for signal intelligence activities.
The WiNRADiO Universal FSK Decoder comes with the following basic protocols pre-installed:
ARQ1000D, ARQ-E, ARQ-N, ARQ-6, ARQ6-70, ARQ6-90, ARQ6-98, ARQ-E3, Baudot, IRA (ASCII),
Packet Radio, POL-ARQ, SITOR-A, SITOR-B, NAVTEX, Raw Bits, SI-ARQ and SWED-ARQ. Many other protocols
can be added by modifying the numerous decoding and demodulation parameters the Universal FSK Decoder
|IBM PC compatible computer
(500 MHz CPU or higher)
Windows XP, Vista or 7
32 MB of RAM, 3 MB of free disk space
SoundBlaster compatible sound card
(or a DSP-based WiNRADiO receiver)
WiNRADiO receiver (1000/1500/3000, G303, G305, G313 or G315 series)