Pickup of radiated electromagnetic field
Here a distant circuit functions as a radio transmitter and radiates electromagnetic waves that fill up all space, but fall off in intensity with distance from the transmitter. If the sensor/measurement circuit picks up these electromagnetic waves then the sensor/measurement system functions as a radio receiver. Unlike inductive or capacitive pickup the source of the interfering signal is distant and so moving the sensor/measurement system will have little effect. The radiated electromagnetic wave has both electric and magnetic fields and these are at right angles to each other. The sensor/measurement system will pick the radiated electric field if the sensor/measurement system has a long segment of unshielded conductor parallel to the radiated electric field. The sensor/measurement system will pick up the radiated magnetic field if the sensor/measurement system links radiated magnetic flux. Encasing the signal wire by an electrostatic shield will cause the shield to act as the antenna rather than the signal wire so the antenna current will flow to common and be harmless. Twisted pair or coax will also eliminate the effect of the magnetic field.