On Jan 26, 2007, at 3:30 PM, Ian wrote:
> Definitely not FeldHell. Might be Olivia.
Yes, definitely not Feld Hell, and not Olivia either unless you feed
the Olivia modulator with some non-standard input (i.e., not the
usual Varicode and definitely with no FEC nor any interleaving).
It is though, probably some variant of M-FSK, i.e., FSK with multiple
tones (the class of which MFSK16, Olivia and DominoEX all fall under)
but with more than one tone being active at any time slot. The usual
encoding from Olivia as far as I understand, will only output one
tone at any time slot.
A waterfall display is usually implemented as an FFT (fast Fourier
transform, an approximation of the spectrum) of the audio signal from
the receiver.
Now imagine that you want to project some raster scanned text image
directly onto the waterfall -- each pixel of the text would just be a
point in the frequency-time space of the waterfall. Each column in
the text raster is just be a discrete frequency in the waterfall, and
each successive text raster row is just a different vertical time
slot on the waterfall.
So, to get text projected onto the waterfall, all you will need to do
is to feed each row of the raster image into an inverse FFT to create
the temporal sound samples (i.e., the raster image is in frequency
space). You could do this with a baseband analytic signal which is
the complex output of the inverse FFT, and then mix it with a
quadrature LO into an audible audio passband which you then feed into
an SSB transmitter.
It would be interesting to find out what emission type this would
fall under FCC Part 2.201 and if it is even legal for an amateur to
transmit such a form of signal in the US.
It might fit under some fascimile/image classification using multiple
tones. Perhaps emission J2C? We know it is not encrypted, and it
can be made to fit into a finite passband, and many amateurs already
have equipment that can decode it --- so it could be legal if
documentation is published.
Transmit first and ask Riley for forgiveness later? Not me. I'm not
going to risk my license. :-)
73
Chen, W7AY
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