. The Bell System technical journal . possible to obtaina narrow band with this type of filter. The mid-frequency of theband occurs when . o^{2k + h) .sm = 0 or when Jm -r- V - All + 2/2 The characteristic impedance of this type of filter becomes very highfor narrow-band filters as is shown by equation (16). At the mean 282 BELL SYSTEM TECHNICAL JOURNAL frequency/m the impedance of the filter is K tan 7r/2 1 + 2/1 tan 1 + /i k 1 4- —^2/1 4/1 —j- Zoi for narrow bands. (18) -^. Such a filter would be useful for an interstage coupler to couple to-gether the plate of one screen grid or pentode tub
. The Bell System technical journal . possible to obtaina narrow band with this type of filter. The mid-frequency of theband occurs when . o^{2k + h) .sm = 0 or when Jm -r- V - All + 2/2 The characteristic impedance of this type of filter becomes very highfor narrow-band filters as is shown by equation (16). At the mean 282 BELL SYSTEM TECHNICAL JOURNAL frequency/m the impedance of the filter is K tan 7r/2 1 + 2/1 tan 1 + /i k 1 4- —^2/1 4/1 —j- Zoi for narrow bands. (18) -^. Such a filter would be useful for an interstage coupler to couple to-gether the plate of one screen grid or pentode tube to the grid of anotherone. One such arrangement is shown in Fig. 3. This method ofcoupling together two stages of vacuum tubes has an advantage overusing a coaxial conductor or a coil and condenser as a tuned circuiton several counts. In the first place the width of the band passed canbe accurately controlled and a flatter gain characteristic is will be shown later, distributed capacity in the plate and grid of the. Fig. 3—Coaxial band-pass filter used to couple vacuum tubes. vacuum tube can be absorbed in the filter by making the line length hshorter. Since only half of the total distributed capacity has to beabsorbed on each end of the filter, a higher impedance can be built upin the filter for the same band width, and hence more gain per sectioncan be obtained than with a tuned circuit. The filter will have other pass bands at 2fm, Sfm, etc., but these donot usually cause any trouble at the short-wave frequencies because thegain in the vacuum tube is falling off very rapidly and no appreciablesignal is passed. If desired, however, another band-pass filter can beadded which has the same fundamental bands but different overtonebands, and this will eliminate the effect of the additional pass very narrow bands, the line length h can be made longer and hencemore realizable by making the characteristic impedance Zo, anything is to be gained b
Size: 2331px × 1072px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
