Hi Jinx, I think Oatley had some doppler radar
modules pretty cheap, with instructions. These
are quite directional (narrow cone) and would
do what you need I think.
-Roman



Jinx wrote:
>
> Is it possible to have two low power transmitters (different
> freqs) next to each other and have one radiate 180 degrees
> in one direction and the other radiate 180 in the opposite
> direction ? I've been asked to look at making a unit that will
> detect when an object goes past a certain point. The object
> has a device that is off on this side of a line (influenced by freq1)
> and switched on when it crosses a line (influenced by freq2).
> It has to be brought back into the influence of freq1 to change
> state again. If it goes past the range of freq2 it will stay
> switched on. I thought perhaps the transmitters could be
> separated by metal plate or mesh shaped to funnel or block
> the radiation pattern. The power needed is just enough to
> extend perhaps 20ft this side of the line and 10ft the other
> side, frequencies unknown at this stage. Any other type of
> detection system (IR, US, laser etc) is probably not practical
>
> TIA

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