Kantronics KPC-2400 used QAM and was regularly used to
modulate FM transmitters. I don't even know of anyone ever
successfully using it through a linear transmitter. I remember
it well as it was the last modem I did for AEA for the DSP-x232
box. It is V.26B tones and a royal pain in the butt.
Bob
At 07:25 AM 11/30/1999 +0000, you wrote:
>> 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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