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



Hello Achim and Kaj,

The dynamic range is determied by the level of the signal artifacts produced by
the ADC and these get worse as the RF frequency goes up. The AD9244 has a 90 dB
dynamic range when the input signals are limited to 45 MHz. By 240 MHz the
dynamic range has dropped to 70 dB.

I was planning to convert the RF to 10.7 MHz and digitize there to get the best
performance out of the ADC. I've got a partially assembled receiver board with a
350MHz 2MHz-wide first IF and an assembled but not yet tested 60-2150MHz LO
board. Transmitting is easy. You can get quadrature modulator chips for
50-3500MHz so all that is needed are baseband I and Q signals. That's why my DSP
board has two DACs.

73,

John
KD6OZH

----- Original Message -----
From: "Achim Vollhardt" <avollhar@physik.unizh.ch>
To: <kaj.wiik@iki.fi>
Cc: "AMSAT Bulletin Board" <amsat-bb@AMSAT.Org>
Sent: Tuesday, 30 March, 2004 07:30 UTC
Subject: Re: Proposal: SDR-DSP receiver (was: Re: [amsat-bb] Cube sat and DSPs
(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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>


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