- Coherent CQ
- Specialized Digital Signal Modes
Coherent CQ is technique centered around a bit rate often called a "clock rate." This uses precisely calibrated transmitters which key at a very stable and specific rate. This consistency allows receivers to use extremely narrow-band filtering. While the transmission rate is very slow, the super narrow-band filtering improves the signal to noise ratio making the technique workable. This can also be used with DSP.
QRSS is another slow speed QRS CW mode used with narrow-band filtering. But this is not based on signal coherence. This uses extremely long time intervals with element lengths of 10 to 30 seconds or longer. FSCW, DFCW, BPSK and WOLF are digital modes that can be used within the QRSS arena.
A number software programs can aid implementation, see below. More here.
- Argo http://www.sdradio.eu/weaksignals/argo/index.html
- Spectran http://www.sdradio.eu/weaksignals/spectran.html
- Spectrum Lab http://www.qsl.net/dl4yhf/spectra1.html