the circuit under test. The operator adjusts the frequency of the GDO until its meter shows its lowest reading (the "dip"). The frequency is read from the dial on the GDO, or the frequency can be measured by finding the dip meter's signal on a well-calibrated radio receiver. Some modern GDOs have a built-in frequency meter, which makes over-coupling somewhat less troublesome. Absorption frequency meter Some dip meters can be used in reverse, as ultra-short-range, tuned field strength meters. The operator finds the frequency at which the highest rise in meter power occurs in the unpowered GDO, when its coil is held near the wires of an active resonant circuit. Since the power in the circuit under test must be high enough to register on the meter, this uncommon method is risky both for the operator and the equipment. See also Absorption wavemeter Antenna analyzer Field strength meter Variable-frequency oscillator External links References Amateur radio Electrical test equipment Electronic oscillators Radio electronics Vacuum tubes