Actually, dolphins already do that.

Kerry


John Gardner wrote:
> That's cool. Why could'nt you do that acoustically?
>
>  =20
>> they linearly
>>    =20
> slewed the transmitter frequency at a given rate and then heterodyned
> the current  tx  signal with the reflected signal. The difference in
> frequency between tx and rx signals gave the time delay and hence
> distance... If you use phase comparisons on tx and
> rx rather than just frequency you can deal with slower to much slower
> slew rates.
>
> Jack
>  =20



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