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Using LP-PAN with CW Skimmer

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 Soundcard Driver. This depends on the sound card used. For the E-MU 0202, you must use MME in both Skimmer and the SDR app. For the E-MU 1212m, use ASIO in the SDR app and WDM in Skimmer. For Quartet, use ASIO in the SDR app, and whichever driver works best in Skimmer.

Select the proper input soundcard in the Signal I/O Device selector, and output soundcard in the Audio I/O Device selector. 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.