> Greg Maxwell wrote:
> > > Note that for QAM modulation you need I/Q modulation and linear TX and
> > > RX
> > > signal paths (due to non-constant envelope). This is non-trivial to
> > > implement,
> >
> > You can do the I/Q modulation in entirely in software. This shouldn't be
> > too hard.
> >
> > As for the linear signal paths.. I'm assuming you mean linear power
> > responce in frequenceny space. This is corrected using a FIR filter.
> > Modems do this.
>
> I assume you don�t mean generating a QAM modulated baseband signal with
> the
> sound card and modulating that FM onto a RF carrier? This would be a
> very funny thing to do, which would be interesting to simulate, but
> I would not expect any performance gain from it.
I don't know if it would work, but why not use modulate it using an AM
radio?
>From my limited knowledge of this subject, the problem of getting QAM to
work with FM radios is down to the amount of AF carrier phases & tones, plus
the modulation of those carriers which would probably get screwed up in the
FM modulation process, or even more if the radio really uses phase
modulation as many so called FM TX's do.
Not long ago I looked at the idea of hooking up a V34 modem to an AM ex-PMR
(land mobile) radio, with the idea of using that as a first stage in a 23cm
or 13cm setup. The PMR radio (A Phillips MX293) worked on VHF high band
(around 140MHz), and would then drive a transverter to the required band.
Since I don't get the time to "play" with these projects at the moment, I
don't mind sharing my ideas, in fact as a radio amateur, I don't mind
sharing them anyway!
It just came to me that we have been brainwashed into thinking that FSK
transmitters are the be-all and end-all of data transfer, but sometimes you
have to take a different view when a problem like this (QAM over a wireless
link) turns up.
Any thoughts?
Has anyone tried using modded (down to 10GHz) 11GHz Satellite TV RX & 10GHz
ATV TX for hooking up 10Mbit ethernet ports? - that's another one for you to
think about...
You need an ethernet adaptor with BNC o/p. The o/p levels will need to be
converted to 1v peak to peak (as per Composite Video). Feed this into your
ATV TX (with no pre-emphasis or filtering), and at the RX, pick up "baseband
video o/p" from the "SCART" connector. Convert that back to normal levels
(which I think are around the TTL area), and feed that back into your
ethernet adaptor. A T-piece is needed at each end, or you can spilt it at
your level converter.
Sounds simple. Should work. Anyone got the time to give it a go?
Back to reality....
How does this 300bd modem work????
Regards
Rob Compton G1ZPU
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