| 摘要 |
1,070,249. Automatic volume control; radio signalling. WESTERN ELECTRIC CO. Inc. Feb. 4, 1966 [Feb. 9, 1965], No. 4955/66. Heading H4L and H4R. In a wideband repeater amplifier, e.g. in a satellite, which relays signals in any one or more of a number of different signal transmission frequency bands, the total power applied to the amplifier, which may be a travelling wave tube, is adjusted to the optimum for the particular number of simultaneously present signals by an automatic volume control which incorporates a comparator and a reference level in the control circuit, in which the reference level is adjusted in accordance with the number of signals present at any one time. In the embodiment of Fig. 1 the signal after pre-amplifier 13 is applied to a bank of band-pass filters 17a to 17g distributed aoross the transmission band of the repeater. The filter outputs are rectified in rectifiers 18a to 18g and applied to monostable triggers to cause outputs on the lines to summing network 20 so that the level on the output of summing network 20 is proportional to the number of signals being transmitted. The summing network output is applied to switches 21 1 to 21 4 and these switches are operated in accordance with the level of the input signal to provide the appropriate reference level to the comparator circuit 22. In comparator 22 a signal from monitor 14, depending on the total power in the transmission, is compared with the reference level, dependent on the number of individual signals, to produce a control voltage for the variable impedance device 12 which is controlled to provide the optimum power level having regard to the number of signal channels in use. In the described embodiment the out. puts of the 17b-19b, 17d-19d and 17f-19f, are arranged to be negative relative to the outputs of the remaining channels and it is shown that with the possible arrangements of channels peculiar to this particular system, some channels being wider than others, the output of the summing network is always proportional to the number of channels in use since the wider channels always overlap three band-pass filters, e.g. 17a, 17b and 17c, two of which, 17a and 17c, result in a positive signal to the summing network with one negative signal, from 17b, so that the net result is one positive signal input to the summing network. |
