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Cube sat and DSPs (was Re: cube sat)

Keith N6ORS writes:
>a transponder with any width would leave everyone 
>milliwatts of power

True, but I'll take those few milliwatts over zero watts any day!

The (LEO) FO-20 transponder was approximately 100 kHz 
wide and ran just two watts output. [ Source: Satellite 
Experiment's Handbook 2nd ed. page B-16 section 3.4 ].  
The (HEO) AO-13 mode S transponder was 36 kHz and 
ran just 1.25 watts. [ Source: Ibid. page B-5 section 3.4 ]

>I would like someone to find me a RF DSP and support 
>chips that could process a whole frequency band that 
>uses about 1/2 watt!  

Someone with more knowledge of DSP chips than me might be able
to suggest an even lower power DSP chip.  I don't know the 
power requirements of many DSP processors, but the DSPx uses 
much less than 1/2 watt and it should be able to process a 
transponder's worth of bandwidth.  

The DSPx analog-to-digital and digital-to-analog converters 
will run at a sampling rate of up to 96 kHz.  Ideally, this
would yield approximately 48 kHz of bandwidth at audio. 
[Source: Nyquist :-) ] The DSPx consumes approximately 
225 milliwatts and runs at 80 million instructions/second.

Now, converting the RF input down to the audio range, 
where the DSPx's ADC can process it, with the remaining 
275 milliwatts (of that 1/2 watt power budget) is left as 
an exercise to the reader, but should be achievable in a 
simple receiver.  QRP kit type receivers typically use 
much less than 275 milliwatts on receive.

In addition, there are open source applications already written
for the DSPx and free development tools.  If someone does launch a
DSP processor, factors such as free and open tools and a known
architecture will help to increase your pool of available DSP 
programmers from among the ranks of amateur radio operators.  

By the way, if anyone is going to launch a digital signal processor,
I'll sign up to write DSP code !  

If I've made any mistakes on any of the above, please correct me.

Douglas KA2UPW

Disclaimer: I don't think that the DSPx is actually space-qualified.
I offer it only as an example of a DSP processor that fits
the above 1/2 watt power budget and should be able to process 
enough bandwidth for an actual transponder.  I am not connected 
financially with the DSPx, it's just the DSP processor that 
I looked at most recently.

Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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