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G305 demodulators are DSP software plug-ins which fit into the G305
control panel. All the last IF (intermediate frequency stage) and the
demodulation stage functions are performed in software. Having been
freed from hardware constraints, this brings about unprecedented level
of flexibility and performance to the receiver.
The G305 is being introduced with two demodulators,
with others to follow. The Standard Demodulator is included as a
standard part of the package, while the Professional Demodulator
is optional.
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The G305 Standard Demodulator provides excellent
performance with minimum adjustable parameters, and facilities exceeding
those of a demodulator of a conventional shortwave receiver in this
price range (such as real-time spectrum scope).
The optional Professional Demodulator goes yet
another step further and offers additional demodulation modes, and fully
user-adjustable demodulation parameters, complete with interactive block
diagrams of the internal structure of the demodulator, an additional
dual real-time spectrum scope with vector voltmeter, SINAD and THD
measurement, and many other facilities. This is a serious tool for a
serious experimenter. |
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G305 Standard Demodulator
Standard Demodulator with Wide-FM option installed.
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This demodulator is supplied as standard part of the G305
receiver package. It features AM, AMS (synchronous AM), AMN (narrow band
AM), LSB, USB, FM6 (6 kHz FM), FMN (15 kHz FM) and CW modes, with fixed
bandwidths (the FMW mode is optional). There is a real-time spectrum
scope which shows the actual situation on the received band.
An interesting feature is Software AGC (i.e. digital
AGC, in addition to the conventional analog AGC). The dual-loop AGC of
the G305 receiver makes it possible to process the weakest as well as
the strongest signals with equal clarity.
As the power of an ordinary PC does not yet allow to
process the bandwidth of a wide-FM modulated signal (broadcast FM)
directly, the option to receive wide-FM is offered separately. The
Wide-FM Demodulator Option is based on conventional hardware (i.e.
it is not software-defined) as an independent "receiver in a receiver".
If this option is installed and selected, the real-time spectrum scope
shows the demodulated signal audio spectrum instead of the radio
frequency spectrum. |
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Clicking the Setup button, another window opens,
making it possible to adjust the necessary minimum number of parameters
for optimum performance:
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The user adjustable parameters include the sound card
selection, sampling rate (48000 samples/sec is recommended, 44100 can be
also used), and the sound card input gain.
A clipping (input level overload) indicator and a CPU
usage meter are also provided for the user's convenience.
With a minimum of initial set-up, the demodulator (and
so the G305 receiver) are ready to go! |
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G305 Professional Demodulator
Professional Demodulator with Wide-FM option
installed.
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This advanced demodulator is offered as an optional
extra. It adds DSB and ISB modes, additional Audio AGC settings and
continuous IF bandwidth adjustment (from 100 Hz to 15 kHz). There are
also user-definable IF bandwidth preset buttons at the bottom.
Many more exciting facilities are hidden under the
Setup button: Optimized filter settings make it possible to increase
the receiver sensitivity typically by 2 dB on AM, SSB and FM; and by up
to 10 dB on CW. |
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The Professional Demodulator Setup window offers many
additional facilities: In the section on the left, user-specified AGC
constants and Secondary output have been added. The secondary output
makes it possible to pass the demodulated signal data directly to
third-party signal processing applications, for example software decoders.
For this, the WiNRADiO optional
Digital Bridge™ Virtual Sound Card is useful to facilitate
such seamless connection. In the section on the right, the demodulator
parameters (such as the digital filter lengths which directly influence the
receiver's selectivity) can be adjusted by the user. There are separate
"tabs" for independent setting of each of the eleven demodulation modes.
There is also a facility to graphically adjust the desired passband of the
audio filter, and a set of ten convenient user-definable IF bandwidth
presets separate for each demodulation mode.
Clicking on the View Demodulator Structure button
discloses an interactive diagram of the demodulator structure:
At the top, there is a block diagram showing the structure
of the currently selected demodulator (each modulation mode has its own
demodulator). Below, there are also two spectrum analyzers. Left clicking on
any of the color points inside the block diagram will connect the left
spectrum analyzer to the associated point (the color of the point will
change to red). Right clicking will connect the right spectrum analyzer (the
point color will turn blue).
At bottom left, there is a Vector Voltmeter showing
amplitude and phase differences between the two selected points, at the
cursor frequency.
There are also THD (total harmonic distortion) and
SINAD (signal-plus-noise-plus-distortion to noise-plus-distortion)
meters, to complement this unique instrument.
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G305 Wide-FM Option
Professional Demodulator with Wide-FM option
activated.
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With the standard G305 receiver, the FMW mode button is
disabled and the wide FM demodulation mode is not available. This is
because wide FM demodulation is not possible to be provided as part of
the G305 software-defined radio system, within the constraints imposed
by the processing power of a standard personal computer.
However, wide-band FM demodulation capability is
available as a factory-installed option. This is in fact a
self-contained "hardware-defined" receiver which shares only the main
receiver's front-end and first mixer, but has an independent wide-band
analog processing circuit with a conventional "hardwired" demodulator.
If the Wide FM Option is installed, the FMW
button becomes active. The demodulator spectrum display shows real-time
spectrum of the demodulated audio. In the Professional Demodulator there
is a user-definable audio filter, displayed superimposed over the audio
spectrum and graphically adjustable.
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