INITIAL SETUP
You may find one of two types of microwave receiver/transitter setups at your station. Both of these setups use Gunn diodes to generate microwaves.
The most modern version, Pasco WA 9314B, is the easiest to use, and has a self-contained meter. Align the receiver horn facing the transmitter horn, and plug the transmitter in to turn it on. On the receiver, turn the intensity knob from “off” to “30”. Adjust the variable sensitivity knob for a full scale reading. You can increase the sensitivity later in the experimet if needed. When finished with the experiment, unplug the transmitter, and turn off the receiver.
The older Gunn diode unit uses a DC power supply for the transmitter, and a separate meter for the receiver. Be careful of the polarity from the power supply to the transmitter. The positive (red) connector of the power supply's output must be hooked to the positive (red) connector of the transmitter's input, or the diode will be destroyed. To adjust this device, place the receiver directly opposite the transmitter, and set the meter to minimum sensitivity. Turn on the power supply, and slowly increase the voltage until the diode begins to generate microwaves. You will notice that a further increase in voltage increases the output power until a plateau voltage is reached. After this point, an increase in voltage does not increase the output power. The transmitter should be operated at the beginning of this plateau. Never exceed 15 Volts DC, as doing so would destroy the Gunn diode.
The microwave receiver consists of a crystal diode which produces a current when aligned parallel to the electric field of the incident microwaves. The diode is not sensitive to microwaves whose electric field is perpendicular to its axis. The current from the diode is read by the horn. Be careful of the polarity between the receiver and the meter. The positive (red) connector of the receiver's output must be hooked to the positive (red) connector of the meter's input, or the meter movement may be destroyed. Never connect the receiver to the power supply, as this will destroy the diode instantly.