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A Q meter is a device that tests certain properties of radio frequency circuits. Such devices specifically determine the Q, or quality factor, of circuits as part of routine testing. They have been largely supplanted by other electronic test equipment which records a broader spectrum of useful data for future reference by operators and technicians. It can be difficult to find a Q meter on the open market in many regions of the world.
The quality factor determines the performance of a circuit under use, and measures the damping of the circuit. Something with a high Q has relatively low energy loss, while low measurements indicate high energy loss. In a simple example, when someone hits a bell, it will resonate for several minutes after ringing, putting out progressively smaller waves. On the other hand, an unmolded pudding will only shake a few times after the bowl is jarred, losing energy quickly.
Q meters attach to the equipment to measure its inductance, the amount of energy it can store, along with the resistance and conductance, showing how readily current moves through the circuit. All of this information can be used in a calculation to determine the quality factor. The device may perform this calculation for the user, or it may be necessary to manually do the math. Operators can use a Q meter with a variety of circuits on radios, televisions, and other radio frequency circuits.
These instruments typically provide a direct reading with gauges on the surface of the unit. If the readouts appear unusual, it may need to be calibrated, or it is possible there is a problem with the equipment that may need to be addressed. Technicians who use Q meters do need to maintain them carefully to ensure that all the connections remain sound and functional. This can help people avoid false or misleading measurements, as well as errors that may not be immediately detectable.
Other test equipment allows operators to collect more data. This can be useful to fully assess the properties of a circuit and to provide a complete picture of what is going on inside it. For this reason, the Q meter is not in widespread use. Some older models are still functional and can be used by people who cannot afford newer test equipment or who specifically want to use a Q meter. It is also possible to build one, using instructions found on sites online as well as in amateur radio and other electronics hobbyist publications.