Try using ferrite sleeves on one or both ends of the cable.
Even better would be to reduce the noise created at the source (instead of removing it later).
Ferrite sleeves, screening, carefully placed ceramic capacitors with short leads or a combination of these will help.
Depends on what the wiring is for. If they are power cables, then heavy
decoupling/filtering at the PIC may help. If they are signals, then perhaps
you could use differential signalling instead of single ended.
Is shielding the source of the noise an option? e.g. resistive/inductive HT
Mike, maybe David is very new to electronics and doesn't know about common
mode rejection, so here goes an oversimplified explaination -
When sending signals over a sigle wire near to big, changing electric fields
the wire can pick up some of the external signal. If the external signal
produces a positive volt or two in your signal wire you have a problem.
However if you pre-process your signal to produce the original signal and a
mirror image of it you can send that [differential] signal along 2 wires to
a reverse pre-processor at your receiver. Both of the wires receive the
*SAME* electrical interference, so the positive going signal gets a little
more positive while the negative going (reversed copy) gets a little less
negative. The reverse pre-processor just takes the mid point between the
signals as being 0 and therefor *REJECTS* the common (to both wires) mode
The pre-processor|reverse pre-processors are cheap and robust.