WinradioG31DDC vers 1.18When the test file is played with WinradioG31DDC, the screen may look like figure 1. It depends of course how the parameters in WinradioG31DDC are set.
Fig 1. WinradioG31DDC running sim1.wav. (excalibur-sim.ddc)
The loudspeaker output from WinradioG31DDC sounds like this:
sim1-excalibur.mp3 (496440 bytes.)
The on-off keyed signal is at a level that is similar
to the noise floor level in the beginning and end of the
file where the data comes from an old Perseus recording.
There are no spurs. The AGC release time can be set short which is a good thing, but the box that should limit the gain to 115 dB does not work. That is why the noise is so strong when the -120 dB signal is in its off state. The AGC problem makes the images look as if the final filter does not quite have the stop band attenuation one would expect. The AGC turns up the gain to a level it would never reach with the hardware connected. With the noise floor of real hardware, the gain would never reach high enough to make the signal outside the passband visible. The stop band attenuation is in the order of 130 dB.
The tested WinradioG31DDC version was 1.18 downloaded Januari 1 2011. The filter length was 200 in this test (default).
The details of the loudspeaker output are shown in figures 2 and 3 which are waterfall graphs produced by Linrad with sim1-excalibur.mp3 as the input (before conversion to mp3).
Fig 2.The loudspeaker output from WinradioG31DDC when running the test recording sim1.wav. This waterfall graph is produced by Linrad with the loudspeaker output from WinradioG31DDC as input.
Fig 3.The loudspeaker output from WinradioG31DDC This the same as figure 2 at a 10 times higher waterfall speed. The signal activates the AGC when it is about 5 kHz away from the passband.
|The loudspeaker output of WinradioG31DDC on an oscilloscope looks like figures 4 and 5 at different X-axis magnification.|
Figs 4 and 5The loudspeaker output from WinradioG31DDC in the time domain when the signal sweeps across the filter.
The limitations in the WinradioG31DDC software,
the inadequate filtering that makes a carrier 5 kHz away from the
passband trigger the AGC is not as bad as it looks with this test recording.
If the same test were done with a real signal into the Excalibur hardware,
the limitation might be the sideband noise of the Excalibur hardware.
Note that one can set a much longer filter than the default 200 and
that then the filter performance is perfectly adequate for the
The non-working gain limitation for the AGC in vers 1.18 makes it
hard to see the effects of a changed filter length unless the filters
are made very long.
Not seeing any effect of doubling the filter size I did not
try very long filters when performing this first test on the
Repeating the test with e.g. a filter length of 4000 would
show that the filters are fine despite the AGC problem.
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