Re: [amsat-bb] DSP based High Speed Data

["laura halliday" <marsgal42@xxxxxxxxxxx>]

bronson@eece.maine.edu wrote:

>Being curious about this High Speed Data stuff, I thought I?d try to put
>some numbers to the idea
>presneted by John Stephensen, KD6OZH.
>
>I?m new to DSP, but here goes anyway;
>
>Given the following:
>
>No info in the amplitude.
>20KHz audio upper limit.
>20Msps 10 bit A/D converter.
>DSP chip that can do the calculations fast enough.
>    a) ignore the DSP processing overhead
>A minimum of 2 data points on the highest Tone (20 kHz).
>    a) and the system can resolve the difference between tones reliably.
>
>Question:
>
>    How do I get some serious bit rates (200Kbps or better) out of this
>stuff?

You don't.

To support 200 kbps in a 20 kHz bandwidth requires an SNR
of 30 dB as a theoretical minimum, with more practical
real-world numbers more like 35-40 dB. I don't recall too
many satellite systems (this is AMSAT, after all) with
such signal strength.

Once you have defined the bandwidth, you have also defined
the minimum sampling rate - 40 ksps in this case. Save
your money and use an audio codec chip, because that's
all you need.

Laura Halliday VE7LDH     "Que les nuages soient notre
Grid: CN89mg               pied a terre..."
                                   - Hospital/Shafte
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