Thanks guys for your suggestions. It sounds like the radio altimeter
is the way to go. Now all I have to do is get it small and light
enough to fit in the plane along with all the other junk that's going
in there... Should be interesting!

Cheers,
Zik

On 23/06/06, David VanHorn <dvanhorn@microbrix.com> wrote:
> Radar altimiter is actually pretty simple.
>
> Sweep your transmit frequency linearly.
> Mix the reflection with the transmit.
> The product is the the difference between now, and the time it took to go
> down and back again, and since you know what your ramp rate is, you know the
> altitude.
>
> It was simple enough that they could put a tube version in bombs 60 years
> ago.
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