Dear LF Group,
I have put together some hopefully fairly accurate circuit diagrams
of my variable phase modulator and linear BPSK generator
experimental circuits. These are not meant to be fully worked out
projects projects, but are complete functioning circuits which could
serve as a useful basis for experiment.
There are 3 circuits:
Phase keying signal shaper, which takes a raw logic signal (eg.
from a PC serial port) and converts it into one with approximately
raised-cosine shaped transitions.
Linear BPSK modulator, which modulates a 137kHz carrier with the
shaped phase keying data to produce a few V pk-pk BPSK signal
with which to drive a linear PA.
Variable phase modulator, which produces a 137kHz carrier with a
phase shift proportional to the phase keying signal amplitude, and
with the shaping circuit produces "gradual" phase transitions as
discussed a little while ago.
The attached JPEG file shows the variable phase and BPSK
spectra generated by the circuits with 100ms and 50ms transitions.
If anyone is interested, I can send them the circuit diagrams as
JPEG files - they are a bit big for the reflector.
Cheers, Jim Moritz
73 de M0BMU
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