. Practical wireless telegraphy; a complete text book for students of radio communication . ive force for obtaining balance of thebridge. To carry out the measurement, the buzzer is set into vibration and the values of R-1 andR-2 varied until complete silence or a minimum of sound is heard in the telephone P-1. Thevarious quantities are then related as folows: C-x R-2 R-2 = or C-x = X C-n C-n R-1 R-1 If condensers C-x and C-n have different dielectrics, complete silence cannot be obtained,hence a minimum of sound is an indication of balance. To carry out the measurement forlow values of capaci
. Practical wireless telegraphy; a complete text book for students of radio communication . ive force for obtaining balance of thebridge. To carry out the measurement, the buzzer is set into vibration and the values of R-1 andR-2 varied until complete silence or a minimum of sound is heard in the telephone P-1. Thevarious quantities are then related as folows: C-x R-2 R-2 = or C-x = X C-n C-n R-1 R-1 If condensers C-x and C-n have different dielectrics, complete silence cannot be obtained,hence a minimum of sound is an indication of balance. To carry out the measurement forlow values of capacity, the total resistance of the sliding wire bridge, need not exceed 110 ohms. If the aerial and earthwire of an antenna sys-tem be substituted for thecondenser C-x, its elec-trostatic capacity maythus be determined, butit should be borne inmind that the simpleelectrostatic capacity ofan aerial and its ef-fective capacity whentraversed by alternatingcurrent of radio-fre-quency are of differentvalue. This is due to thenon-uniform distributionof current and voltagethroughout the open cir-. Fig. 22S—Measurement of Electrostatic Capacity at Radio Frequencies. cuit which causes the capacity to vary with the applied frequency. Generally the effectivecapacity is less than the simple electrostatic capacity. (The latter value is the capacityobtained by considering the aerial merely as one plate of a condenser, the earth the oppositeplate and with uniform current and voltage distribution.) A standard of capacity for the bridge may be constructed from flat brassplates of rectangular form and its capacity may be calculated by the followingformula: A C = mfds. 4,r T 900,000where A = area in sq. cms. of the dielectric covered by the plates,T ^ separation of the plates in cms.(b) Measurement of Capacity^ at Radio-Frequencies. The capacity of thecondensers used in receiving circuits may be determined by the method shown indiagram of Fig. 228. A wavemeter L, C (or any variable condenser and i
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1917
