Hi,

An RF bypass cap to ground should do it.  Try .001 uF to ground as near to
the input as possible.  If you are in a really bad environment you might
need to make sure your ground is really a ground as RF can bias your supply
rails, particularly if the leads to and from the supply are "resonent"
which essentially means they are 1/4 wave long at the frequency of interest
(or an multiple thereof)

If you find such a situation, I would recommend RF chokes in the ground and
supply leads.  The inductance is a function of frequency.  A small toroid
can be effective, as can be the split cores that wrap around wires.  A
bypass cap having good RF performance of .01 where the leads enter the
board is also important.en

73,
Len WA1IOB

/96 GMT+1100, you wrote:
>Has any one got any ideas to stop RF from causing false readings
>on an input.
>
>Tony
>
>
>Just when I thought I knew it all,
>I learned that I didn't.
>
>