. QST . ntial capacitor is a dual capacitor soarranged that as the shaft is turned the capaci-tance of one unit decreases by the same amountthat the capacitance of the other increases; in abridge, the two capacitors become the variableratio arms. The practical form of W2ZEs circuitis shown in Fig. 2, where Ci is the differentialcapacitor. Ci does not use up any of the inputpower, and when a microammeter is used as anindicator, the circuit will operate well from a grid-dip meter source even with loose coupling. The only fussy part of the bridge is the differ-ential capacitor. For compactne
. QST . ntial capacitor is a dual capacitor soarranged that as the shaft is turned the capaci-tance of one unit decreases by the same amountthat the capacitance of the other increases; in abridge, the two capacitors become the variableratio arms. The practical form of W2ZEs circuitis shown in Fig. 2, where Ci is the differentialcapacitor. Ci does not use up any of the inputpower, and when a microammeter is used as anindicator, the circuit will operate well from a grid-dip meter source even with loose coupling. The only fussy part of the bridge is the differ-ential capacitor. For compactness and reductionof stray effects this capacitor, like the one shownin the accompanying photograph, should be de-signed especially for the purpose. Two identicalsingle capacitors, ganged together so that one isat maximum when the other is at minimumcapacitance, may be usable; however, the fre-quency error will be greater even though theassembly is kept as compact as possible to mini-mize stray Construction The photographs show the construction of abridge l)uilt to \V2ZEs design. As can l)e seen bylooking at the inside view, the unit is not at allcomplicated; however, it is advisable to stick tothe suggested components and layout. Obviouslyit is undesirable to have unnecessary lead in-ductances or capacitances between bridge shown in the inside view of the bridge and inthe photograph of the differential capacitor, acopper shield is placed around the top part ofthe capacitor to shield the stators from the otherelements of the bridge. Since the calibration ac-curacy at the upper end of the frequency range islimited by stray capacitances between bridgeelements, the addition of this shielding raises theupper frequency limit at which the bridge main-tains its accuracy. With the shield around thecondenser the frequency error is very small up toat least 50 Mc. The choke in the bridge is a miniature pow-dered-iron-core layer-wound solenoid. The lead
Size: 1780px × 1403px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectradio, bookyear1915
