6 May 2022
The HamSCI group at Case Western Reserve University has been experimenting with GPS-synchronized coherent CW and recently had its first two-way local QSO and one-way distance decode (Philadelphia, PA to Cleveland, OH, about 540 km on a 40 meter daytime path). Senior project students Olivia O'Brien KC3SXB, Carolina Whitaker KD9NKM, and Ryan Marks KN6RBK were supervised by David Kazdan AD8Y and John Gibbons N8OBJ in the work. Ryan logged his first-ever QSO in the new mode, under Technician privileges of on-off radiotelegraphy on 40 meters.
Coherent CW is an information-theoretic implementation of radiotelegraphy, using tight send-receive synchronization to achieve improved signal to noise ratio in automatic signal reconstruction and, if desired, computerized decoding. In some sense, it is the radiotelegraphy version of FT8, in using an integrating noise detection in well-defined time slots to determine presence or absence of signal. Since it does not use frequency-shift keying to provide continuous maximum transmitted power (it's still on-off keying), the S/N ratio isn't as high as FT8's but it is still considerably higher than other telegraphy implementations.
Its original implementation was with analog signal processing, described by Raymond Petit W7GHM (SK). In modern implementation, digital signal processing techniques may be used with minimal hardware addition to the CW transceiver.
The promises of fully-implemented GPS-synchronized CCW include:
A facilitated entry point to HF operations for Technician licensees and others wanting to use CW while learning it or even without learning it (the FCC privileging for CW doesn't not require amateurs to have any skills at all in manual sending or by-ear decoding of the code).
A new automated data collection mode for ionospheric sounding via HF QSOs that can be used by all licensed amateurs. This will use a modern implementation of time-of-flight measurement through software phase-locked loop timing measurements, first implemented in the MS-DOS CCW programs COHERENT and PRECISION CW (PRECISION CW Software Download (qsl.net)).
An easy add-on to relatively simple HF transceivers to permit use of a keyboard-to-keyboard conversational mode, with better decoding than unsynchronized systems such as fldigi. The CW sending is standard Morse at well-defined speeds, however, and so it will retain compatibility with unsynchronized decoding systems.
Watch this space! We plan more work over the summer including collaboration with several QRP HF CW transceiver manufacturers. Let us know if you would like to participate.
73,
David AD8Y