However, I believe the object of Rik's proposal was to decrease bandwidth
while retaining as much simplicity in the system as possible. If one can
abide the slower phase transitions of the filtered signal, and the modest
increase in bandwidth from not having dragged out the transitions even
further, the technique should work at moderate power levels. It's a
collection of trade-offs, as is anything in engineering.
Hello John and group,
That is 100% correct, my aim is to find a trade-off between simplicity and
bandwidth. This is standard practice for any CW transmitter where
key-clicks are surpressed to an acceptable level. If one would want a CW
transmission with absolute minimal key-clicks the same kind of envelloping
as used with PSK would be needed, the soft keying we use is a compromise.
The main reason why 'rude BPSK' has a relative large bandwidth (compared to
CW) is because :
- the 180 degrees phase jumps are the equivalent of an extreme hard keying
- the BPSK sidebands are 6dB stronger than CW sidebands (this is directly
related to the 1/-1 switching versus 1/0 switching that gives BPSK a 6dB
advantage over CW).
My goal is to make the phase transition 'less hard' in order to reduce the
bandwidth of a (10BPS) BPSK transmission to that of a normal keyed (12WPM)
CW transmission.
BTW, another idea :
What happens if you send a BPSK (instant phase switching) as reference
signal to a PLL ?
The reaction time of the PLL would depend on the feedback circuitery, maybe
this could also be used to get 'soft phase transistions'.
At 136kHz the whole PLL could be incorporated in a single CMOS4046, just 1
cheap IC and half a dozen resistors/capacitors might do the job.
73, Rik ON7YD
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