This discussion assumes that you are going
to use CW Skimmer at the same time as an SDR application like NaP3 or
PowerSDR/IF. This is not required, of course, and most of the
information on this page applies to standalone CW Skimmer use as well.
First,
make sure that LP-Bridge & the SDR app are set up correctly, and
that the
offset
tracks between the K3 and the SDR (signals tuned in on the K3 match
the pitch
of signals tuned in on the SDR). This is covered in the SDR setup pages
under
the
Global Offset calibration.
Open
CW Skimmer > Settings. On the Radio tab, Set the Skimmer Hardware
Type to
SoftRock-IF. Set the Skimmer Sampling Rate to match the rate used in
the SDR.
Ignore the other settings on this tab for the moment.
Click
on Audio tab, and select MME as the Soundcard Driver.
Select
the proper input soundcard in the Signal I/O Device selector, and
output soundcard in the Audio I/O Device selector. The example shows
the ASUS Xonar U7 sound card. If you haven't
already, set
Left/Right
= Q/I in the Channels section. This is required because the sideband
conventions in CW Skimmer are reversed from those is NaP3 and
PowerSDR/IF. Check that "Shift Right Data
Channel by"
is set to 0 samples. Click
on the Radio tab again. Unless you plan to actually listen to the
output of
Skimmer
(not usually the case), the "CW Pitch, Hz" setting can be left at the
default of 600Hz (or any other value).
Set
"Audio IF, Hz" using the following formula...
CW
Pitch + Global Offset =
Audio IF, Hz
For example… 600 + (-6000) = -5400
CW
Pitch refers to the sidetone pitch setting used on the K3. Global
Offset refers to the local oscillator offset used in LP-PAN. Late model
LP-PANs use a standard nominal offset of minus 6kHz (-6000 Hz). The
actual number may vary up to 100Hz from that value, and would be the
same number that you found when setting the Global Offset in NaP3 or
PowerSDR/IF if you use one of these. This will get
you very
close. You can fine tune it by clicking on a signal, and comparing the
resultant pitch on the K3 to the sidetone using the Spot button. Make
sure the
DSP controls on the K3 are set to NOR when you do this. There are a
number of
possible sources for the residual error, but you should be able to
eliminate any errors for your main CW roofing filter.
Note:
The setting will only be dead accurate for one filter,
especially if the filter is a 5-pole. The difference between multiple
8-pole
filters will be much less, although the 8-pole filters have a slight
offset as
well. Also, adjusting the K3 DSP controls off of NOR will shift the
Skimmer
display. Unless the author of CW Skimmer is willing to support the K3’s
“FI” IF
Offset command as the authors of the PowerSDR/ and NaP3 have done, the
DSP shift
problem
has to be lived with. We may add a workaround to LP-Bridge in the
future, but it would by definition cause the CW Skimmer frequency
window readout to show a value that is off by the amount of the DSP
shift. This is not as important as accurate point-and-click capability,
however.
