Electronic apparatus for biological research electronicappara00dona Year: 1958 REAL GENERATORS switches. We shall continue to discuss the Tform, but it must be remembered that these remarks apply equally to the pi configuration, also to the H and O forms, which are only trivial modifications of the T and pi. The 0 of a stepped attenuator may be varied by: (1) changing the resistances in use for three new ones {Figure ); (2) using tapped resistances, which is sometimes more economical (Figure ); (3) having a varying number of fitted T's in cascade (Figure ). Clearly if a number of
Electronic apparatus for biological research electronicappara00dona Year: 1958 REAL GENERATORS switches. We shall continue to discuss the Tform, but it must be remembered that these remarks apply equally to the pi configuration, also to the H and O forms, which are only trivial modifications of the T and pi. The 0 of a stepped attenuator may be varied by: (1) changing the resistances in use for three new ones {Figure ); (2) using tapped resistances, which is sometimes more economical (Figure ); (3) having a varying number of fitted T's in cascade (Figure ). Clearly if a number of attenuator 'sections' are designed to work between a certain generator and load, have the same characteristic resistance, then they can be connected together to form a chain and their 0's will be multipUcative. (4) Having a fijced number of varying T's in cascade (Figure ). Here again, the overall d is the product of the 0's for the several sections. The decibel (abbreviation: dB)—The transmission factor, d, was intro- duced because it enables us to compute the resistance values required for an attenuator section. In dealing with a number of sections, however, there is a much more convenient unit—the decibel. Suppose we have a collection of attenuator sections, all of the same charac- teristic resistance, having d values of 0-1, 0-2, 0-3 .. . 0-9, and suppose we have to make up an attenuator of overall d = 0-126. It takes a little time to see that the way to do this is to use the 0-2, 0-7 and 0-9 sections, whereas no one has any difficulty in seeing which coins from a handful of loose change go to make, say, 6/4d. It is, of course, easier to add than to find factors. Thus, if for our attenuator sections we can find a unit which expresses the input-output ratio and which is additive when sections are connected in cascade, then the calculations become very easy. The Bel is defined as logio y where P^ and /*2 are two powers. Thus the Bel can be used to compare powers
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