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Re: Proposal: SDR-DSP receiver (was: Re: Cube sat andDSPs (was Re: cube sat))



Hello Kaj,
good comments.. i'll reply below.

> On 15:02 2004-03-30, Achim Vollhardt wrote:
>
> > Proposal is to is a 65 MSPS ADC with the digital down converter and
> > DSP.. so possible reception would be somwhere between 0.1 and 30 MHz.
> > Perhaps direct reception of the aliased image of 144 MHz (at 14 MHz)
> > would be possible as well.. a common problem like bad large signal
> > performace is negligible as we deal with sat-downlinks.. we don't
> > have large signals!!
>
> Huh, at two meters, you must be kidding!
>
> What's wrong about
> http://www.proaxis.com/~boblark/dsp10.htm
> with
> http://www.fidalgo.net/~wa7gxd/dspx.html
>

DSP10: you need again a PC to control it.. That's not the idea.
DSPX: could be a building block for my proposal, I already spoke to Lyle
Johnson..



> The sample rate should be compatible with the signal bandwidth, not the
> signal frequency. You'll end up throwing most of the data away and will
> have to deal with nasty problems with high speed logic signals when
> using high speed converters (e.g. 65 MSPS, 10 bit only!).
>

there is some thing called oversampling and coding gain.. I won't describe
this here, but actually you can increase system performance with a 65 MSPS
ADC.. at it is 14 bits, not 10 bits.. so dynamic range is over 80dB.. with
a variable gain amplifier(controlled by the DSP) , you end up with 125dB
range.. should be enough for Sat-operations.

73s Achim, DH2VA
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