I've been having fun with QRSS over the last few weeks. My Arduino controlled DDS-60 has been transmitting "barefoot". i.e, connected directly to an antenna tuner which goes to a balun which feeds the ladder line out to my antenna. It's been running for long periods sending very slow CW using frequency shift keying with about 6 Hz shift.
I'm not sure exactly how much power I'm putting out but I think it's about 15 milliwatts. I adjust my antenna tuner for zero reflected power using my Kenwood TS430S transceiver and then connect the DDS-60 instead. I measure the DDS-60 output with an oscilliscope and assume the tuner is presenting an impedance of 50 ohms.
I've been received or "spotted" once in New Zealand and frequently in UK, Belgium and Italy. This is near 10.140 MHz in the 30m band.
QRSS is a fascinating mode with a community of friendly and interesting people. Claudio, I2NDT runs a web site that shows various receivers or "grabbers" around the world. Scott Harden AJ4VD is doing some great work developing improved grabber software.
There is another mode somewhat similar to QRSS which is called WSPR (Weak Signal Propagation Reporter) or "whisper" as it's pronounced. WSPR was invented by Joe Taylor, K1JT. In many ways, WSPR is more sophisticated and automated than QRSS. The software forms a complete system when connected to an SSB transceiver via an audio interface. It will send and receive and, if connected to the internet, it will send reports automatically to the central web site. The web site has a very cool map showing recent activity.
I have considered the possibility of adding a WSPR mode to the Arduino DDS-60 code. As I understand it, a WSPR signal is FSK with four frequencies so the RF side of it should be achievable. The difficult part is that it needs to know the time of day or at least when time of day minutes begin within about a second. I don't see any way of doing that with the RBBB Arduino board which uses a ceramic resonator for timing.
When the standard WSPR software runs on a PC it uses the system time which is usually synchronized with an internet time server. I think some people have built WSPR hardware that uses a GPS receiver as a time standard.
I have pondered upon the idea of building another microcontroller / DDS-60 device to be controlled from a PC. The Arduino or PIC or whatever would simply act as a communication "bridge" between USB and the DDS-60. Software on the PC could generate WSPR signals using an internet time server. That would eliminate the need for an SSB transmitter and would make a nice small WSPR beacon. That wouldn't cover receiving and I think to be a "good citizen" of the WSPR community you really should act as a receiver as well as a transmitter. Even with QRSS I felt a bit guilty because I was only transmitting. On WSPR you certainly shouldn't transmit 100% of the time but even with an appropriate transmit / receive ratio, I think Joe's intention is that you should be receiving and reporting during your key up times. I need to give this some more thought and investigation but it's probably not something I'll get into any time soon.
By the way, Joe Taylor is a Nobel Prize winning physicist. His biography on the Nobel Prize web site mentions ham radio and is interesting reading.