Active and Passive Sensors
Active sensors are sensing devices which contain active components; usually this solution allows for a more precise measurement with respect to passive components. In fact, a passive receiving antenna collects energy from the electromagnetic field being measured and makes it available at a RF cable connector. This signal then goes to the spectrum analyzer but the field characteristics can be someway modified by the presence of the cable, especially in near-field conditions.
On the other hand an effective solution is to transfer on an optical carrier, the electric (or magnetic) field component sensed with an active probe. The basic components of the system are a receiving electro-optical antenna which is able to transfer, on an optical carrier, the individual electric (or magnetic) field component picked up and to return it in the form of an electrical signal at the output port of an opto-electric converter.
The modulated optical carrier is transferred by means of a fiber-optic link to a converter which extracts the modulating signal and converts it back to an electrical signal. The electrical signal thus obtained can be then sent to a spectrum analyzer with a 50 Ω common RF cable.
Read more about this topic: EMF Meter
Famous quotes containing the words active and, active and/or passive:
“Even if you find yourself in a heated exchange with your toddler, it is better for your child to feel the heat rather than for him to feel you withdraw emotionally.... Active and emotional involvement between parent and child helps the child make the limits a part of himself.”
—Stanley I. Greenspan (20th century)
“True contentment is a thing as active as agriculture. It is the power of getting out of any situation all that there is in it. It is arduous and it is rare.”
—Gilbert Keith Chesterton (1874–1936)
“To make oneself an object, to make oneself passive, is a very different thing from being a passive object.”
—Simone De Beauvoir (1908–1986)