The Illustrated Dictionary of Electronics - Loscha

328 half-wave loop antenna • Hall fieldhalf-wave loop antenna A loop antenna having acircumference of 0.5 wavelength with a break oppositethe feed point. It is, in effect, a HALF-WAVEDIPOLE bent into a circle or square (although anysymmetrical configuration can be used). The circleis the most efficient configuration.Gaphalf-wave vibrator A vibrator (see INTERRUPTER)whose reed operates against only one stationarycontact. Compare FULL-WAVE VIBRATOR.half-wave voltage doubler A voltage-doubler circuitwhose direct-current (dc) output has a ripplefrequency equal to that of the alternating-current(ac) supply. Although its output is harder to filterthan that of a full-wave doubler, this circuit hasthe advantage of a common ground. CompareFULL-WAVE VOLTAGE DOUBLER.λ/4λ/4C1100 V− +D2100 Vac+−D1C2200 Vdchalf-wave loop antennahalf-wave radiator An antenna consisting of a single,usually straight, active element that measuresan electrical half wavelength from end toend. It is therefore a resonant element. A simplehalf-wavelength (λ/2) conductor with a highlength-to-diameter ratio measures approximately95 percent of λ/2 in free space. The element can bemuch shorter than free-space λ/2 yet remain λ/2-resonant if inductance is inserted in series withthe radiator. The element can be much longerthan free-space λ/2 yet remain λ/2-resonant if distributedcapacitances are inserted in series withthe radiator.half-wave rectification The conversion of alternatingcurrent (ac) to direct current (dc) duringhalf of each ac cycle. Also see HALF-WAVE REC-TIFIER.half-wave rectifier A rectifier that delivers a halfcycleof direct-current (dc) output for every otherhalf-cycle of applied alternating-current (ac) voltage.Because the successive dc half-cycles are180 degrees apart, they have the same polarity.Compare FULL-WAVE RECTIFIER.half-wave transmission line A transmission linemeasuring 0.5 electrical wavelength at the transmissionfrequency. The physical length is somewhatless than a free-space half wavelengthbecause of the VELOCITY FACTOR of the line.half-wave voltage doublerhalide A compound of a HALOGEN. Examples:sodium iodide, used as a scintillating crystal; ammoniumchloride, used as the electrolyte in a drycell.halide crystal A halogen-compound crystal, suchas mercuric iodide and sodium iodide, useful indetecting radioactivity.Hall coefficient For a current-carrying conductor,the constant relationship between the Hall(transverse electric) field and the magnetic fluxdensity.Hall constant For a current-carrying conductor,the constant of proportionality k given by theequation k = e/(im), where e is the transverseelectric field (Hall field), i is the current density,and m is the magnetic field strength.Hall effect A phenomenon observed in thin stripsof metal and in some semiconductors. When astrip carrying current longitudinally is placed in amagnetic field that is perpendicular to the strip’splane, a voltage appears between opposite edgesof the strip that, although feeble, will force a currentthrough an external circuit. The voltage ispositive in some metals (such as zinc) and negativein others (such as gold). Also see ETTING-HAUSEN EFFECT, NERNST EFFECT, andRIGHT-LEDUC EFFECT.Hall-effect modulator A device that uses the HALLEFFECT to modulate a signal, or to mix two signals.Hall-effect multiplier A device based upon theHall generator and used in analog mathematicaloperations, such as multiplication and the extractionof roots.Hall field The transverse electric field of a conductorcarrying current in a magnetic field.