Electronics:  Basic Terms

alternating current (AC): An electric current that has one direction during one part of a generating cycle and the opposite direction during the remainder of the cycle.  Think of one period of a sine wave as one cycle of an alternating current.

amplifier:  A device used to increase the amplitude of a signal.

capacitor:  A capacitor is a passive electronic component that stores energy in the form of an electrostatic field. In its most basic form, a capacitor consists of two conducting plates separated by an insulating material (the dielectric). In this experiment, however, there is only air between the capacitor plates.  The capacitance is directly proportional to the surface areas of the plates and inversely proportional to the separation between the plates.

direct current (DC): An essentially constant-value current in which the movement of charge is in only one direction.

impedance: The ratio of the effective voltage to the effective current in an a-c circuit (reactive resistance).

mixer:  A nonlinear circuit or device that accepts as its input two different frequencies and presents at its output (a) a signal equal in frequency to the sum of the frequencies of the input signals, (b) a signal equal in frequency to the difference between the frequencies of the input signals, and, if they are not filtered out, (c) the original input frequencies.  This device acts like a signal multiplier.

To see the calculations that allow one to determine the signs of the signals entering the mixer, click here.

oscilloscope: An electronic device which measures 2 things: voltage and time (and with time, often, frequency). An electron beam is swept across a phosphorescent screen horizontally (X direction) at a known rate (say 1 sweep in a millisecond). An input signal is used to change the position of the beam in the Y direction. The trace left behind can be used to measure the voltage of the input signal (off the Y axis) and the duration or frequency can be read off the X axis. This is the definition of an analog scope; a digital scope has the same function but works in a different way.

splitter (0 degree): A passive device which accepts an input signal and delivers multiple output signals.  The output signals have equal amplitude, a 0 degree phase relationship, and high isolation between each output signal.

splitter (180 degree): Like a 0 degree splitter except that the output signals through this splitter have a 180 degree phase relationship.

synthesizer: This device produces an AC signal at a chosen frequency and amplitude.


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