. The Bell System technical journal . S2 = Thus, in this case, the side- 1band *Si is down 6 db from its value when the amplifier is operating inthe linear region. When there is conversion of AM-to-PM in the amplifier, the situationbecomes somewhat more complex. Suppose an AM signal is fed into theamplifier and that its voltage is given by V = Vi{l -\- a sin wj) sin Uct where coc and oom are the carrier and modulating radian frequencies andV\ and a are constants. The outputs will be given by V = KVi[l + «(1 — c) sin oo,nt] sin {coct + kpa sin co^O (5) Here K is the amplification, c is the
. The Bell System technical journal . S2 = Thus, in this case, the side- 1band *Si is down 6 db from its value when the amplifier is operating inthe linear region. When there is conversion of AM-to-PM in the amplifier, the situationbecomes somewhat more complex. Suppose an AM signal is fed into theamplifier and that its voltage is given by V = Vi{l -\- a sin wj) sin Uct where coc and oom are the carrier and modulating radian frequencies andV\ and a are constants. The outputs will be given by V = KVi[l + «(1 — c) sin oo,nt] sin {coct + kpa sin co^O (5) Here K is the amplification, c is the compression factor and kp is a factorwhich is a measure of the AM-to-PM conversion. It is seen that kp isthe output phase change for a given fractional input change a. Thus rCp — A^ a (6) where AO is the phase change in radians caused by a fractional inputchange a. Later on it will be desired to express kp in terms of degreesphase shift per db change in input amplitude. To express a in db we i(i-c) ^ AMVECTORS 4^ PMVECTORS (a). (4) Fig. 42 (a) After passing through an amplifier in compression tlie AM sidebands arereduced in amplitude but the PM sidebands are unaffected. The lower two side-bands which represent a signal at frequency fi — Af no longer cancel and so thereis a net signal at that frequency. (b) The locus of the resultant signal now assumes an elliptical shape. TRAVELING WAVE TUBE FOR 6,000-MC RADIO RELAY 1339 lust evaluate 20 logio ( 1 + a). The quantity loge (1 + a) can be ex-)anded in a series to give loge (1 + a) =a — -a-\--a+ • • • . long as a <3C 1, we can approximate it by taking only the first term ofthe above expression. Converting to the base ten and converting AdProm radians as it appears in (6) to degrees, we find that k. Ad (in degrees)A input level (in db) (7) Now let us consider the case in which the signal of Fig. 41 is putthrough an amplifier having AM-to-PM conversion. Fig. 43 shows thevector picture of the resulting sig
Size: 1002px × 2494px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
