On using CW Skimmer with the SDR-IQ wideband
- Hi All,
If you have a SDR-IQ you know what a great receiver it is. Now there
is a new version of SpectraVue, available at
that can connect to CW Skimmer in wide bandwidths. In order to enable
direct I/Q output, simply uncheck demod and press Start. Next you need
to route that I/Q signal to CW Skimmer.
I have concentrated on 50, 100, and 190khz, and routing the I/Q signal
rather than through a soundcard, which has some problems, through a
VAC "virtual cable", which works much better. Here's why.
The exact sample rate output from the SDR-IQ and from SpectraVue at
each of these settings, along with the corresponding CW Skimmer
indicated actual Skimmer
--------- --------- -------
50khz 55,554hz 48khz
100khz 111,108hz 96khz
190khz 196,073hz 192khz
Note that the frequency expected by CW Skimmer is slightly different
than the output of SpectraVue. It is possible to use VAC automatic
resampling to correct this. Simply piping the signal from SpectraVue
to CW Skimmer through a virtual cable with the SR range set
appropriately will give a reasonably good result.
However if you look closely at the CW Skimmer waterfall display there
may be artifacts such as weak images of signals repeated above or
below the actual frequency. This is because the resampler in VAC is
designed for the audio spectrum, and is introducing harmonics when
wideband I/Q signals are converted.
In order to overcome the distortion introduced by the VAC resampler
Alex VE3NEA has developed a custom filter designed specifically for
this purpose. I have been testing it here with excellent results. I
believe his plan is to introduce this capability in the next version
of CW Skimmer.
But in the mean time plug up some VAC cables and enjoy!
73 Ed W2RF