@ftevised 6epcember 198o)
CCWN 77:129



error causes a weak mark just before each dot or dash. A slight lag error causes a weak mark
just after each dot or dash.



Operating Practices
     Three parameters of the incoming signal are needed for reception, the frequency, the
frame length, and the frame phase. Frame phase acquisition usually has been accomplished by
tuning. Operating practice is to send a 15 second stream of dots to help in frame phase acquisi-
tion. A steady carrier for 10 seconds also is verv helpful in fine tuning frequency, since tuning
needs to be within a fraction of a Hz for best results.
     Under favorable conditions, it is often convenient to operate the coherent filter at shorter
than optimal frame periods. For example, at .01 second frames, the bandwidth is around 90 Hz
and the phase adjustment makes little difference. Although selectivity is reduced and sensi-
tivitv is reduced by 10 dB, this mode is useful for detection of a signal or location of a signal
within a small frequency range. Once a signal is located, phase adjustment and longer frame
periods may be used to optimize reception.
     Fine tuning of frequency is important because if the frequency is not very close, the
phase will rotate as well. In the Petit filter this produces transients which sound like clicking. I
and K'/KK have found these a useful audio indicator for fine tuning a signal. I have used a low
pass filter to suppress these clicks but they are not a problem with a properly tuned signal. The
low pass filter also improves the sound of the tone by rounding the otherwise square wave.
This is less apparent with DX signals because these signals are broader due to propagation
modulation.

     One of the operating alternatives is frame phase tuning versus frequency tuning. We
have used an agreed upon frame and frequency, and tuned for frame phase by adjustment of
the phase lag in the filter. Once frame phase adjustment is close, frequency may be fine tuned
as well.
     It is also possible to adjust the keying and the reference frame to make receiving filters to
be in phase with the time second pulses of a time reference such as WWV. This operating
technique must take into account the electromagnetic distance of the standard to each station,
and the electromagnetic distance between the stations. To do this allows phase to be fixed and
therefore allows frequency to be the primary parameter tuned. We have successfully done this
JA-W6, but it is a lot more trouble than phase tuning.
     Currently the following frequencies are being used for ccw meeting frequencies and fre-
quencies for CW stations to meet to discuss ccw. 14,049,000-, 21,049,000 and 28,049,000. we
suggest that stations QSY once contact is established.



Conclusions
     Coherent cw is a very useful technique which gives over 20 dB improvement in communi-

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cation effectiveness over ordinary cw methods. It requires that three parameters of the signal,
frame length, frame phase and frequency be precisely controlled. It has the potential to be as
revolutionary to cw as ssb has been to phone communication. It makes more efficient use of
the available spectrum. The improvement in communication effectiveness can be used to offset
poor propagation, small antenna, poor antenna location or low power.