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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.

</But-I-digress=ON>
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 !  
</But-I-digress=OFF>

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.

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