Optimizing the SunSDR2 for CW Operation

The SunSDR2 from Expert Electronics is a very powerful and flexible SDR transceiver package. The software that runs the show is stable and packed full of amazing features (like CW Skimmer integration built-in). While it performs well on CW, like most SDR radios it has a few issues with high speed CW >25 wpm.

The Sun utilizes semi-breakin CW with some nice customization settings. When using the built in keyer, the timing of CW character elements is excellent even at high speed, with no noticeable shortening of the leading element. However, it doesn't have QSK capability (the ability to hear between CW elements) because its T/R switching is not fast enough (QST measured 123ms).  While I would not place this radio in the top tier of CW performance, it is overall a very competent radio.  

However, there is one issue that I needed to address. When the internal keyer is turned off and the radio is keyed with an external keyer, the first element in a Morse sequence is truncated a bit (noticeable only above about 25 wpm). Fortunately, this shortening can be corrected. 

The ExpertSDR software has a very cool transmit signal analyzer that can display the timing of Morse elements. At 30 wpm or so, you can clearly see the truncated elements. Using the built in analyzer, I was able to easily compensate for the shortening by adjusting the break-in timing. 

These are the settings I derived for the SunSDR2 Pro when using an external winkey:

• On the ExpertSDR breakin tab, set the breakin time to 225ms or higher. (keep the rise time at 7 or higher to avoid key clicks!)
• Play around with these settings a bit and observe the effect on the tx analyzer
• Set the PTT delay to at least 10ms. (Longer will shorten dits and shorter is not advised). 

Below are before and after screen shots when using an external keyer. Note the shortening of some of the dits when using an external keyer. 

Click to Enlarge Image

Below is a screen shot after compensating for the first element shortening. Note the uniformity of the dits. 

                                

July 2025 Update. The best way to fully correct for the first character shortening is with Winkeyer. The menu feature is called "First Character Extension" and the setting is available in WinK3 tools (for standalone operation) and in N1MM Winkey configuration (for contest operation). The extension should be set for 10ms.