GB942847A - Improvements in or relating to transmission networks - Google Patents

Abstract

942,847. Attenuation equalizers. PHILIPS ELECTRICAL INDUSTRIES Ltd. June 14, 1961 [June 17, 1960], No. 21470/61. Heading H3U. An attenuation equalizer comprises a stepwise adjustable parallel LC circuit consisting of a coil which has at least four connection points for the capacitor which divide the turns of the coil in the ratio 1 : a a<SP>2</SP> where a is given by 1 +a = a<SP>3</SP>, i.e. a = 4/3. As shown, the equalizer consists of a T-network of resistances having the configuration shown, the series and shunt branches being provided with terminals, respectively 13, 12, across which are connected the adjustable LC circuits. These provide respectively increases and decreases in attenuation at a number of fixed resonance frequencies and the magnitudes of the increase and decrease at each frequency are equalized by means of the variable resistors 18, 19. Each LC circuit consists of a coil 14 having terminals 20-23 the number of turns between successive terminals 20-21, 21-22, 22-23, 20-22 being w, aw, a<SP>2</SP>w and (1+a)w + a<SP>3</SP>w. This division further results in a number of turns a<SP>4</SP>w and a<SP>5</SP>w respectively between terminals 21, 23 and 20, 23. Thus, the capacitor 15 may be connected across six different pairs of terminals on the coil 14 to obtain a series of increasing resonance frequencies F 6 . . . F 1 which, being proportional to the numbers in the sequence 1, a<SP>2</SP> . . . a<SP>5</SP>, are equidistantly spaced on a logarithmic scale. With a fixed connection for the capacitor 15, the resonant frequency remains constant and independent of the manner of connection between terminals 20-23 and terminals 12 or 13. However, it can be shown that the six possible modes of connection provide six bandwidths B 1 . . . B 6 proportional to the numbers in the sequence 1, a<SP>2</SP>, a<SP>4</SP> . . . a<SP>10</SP> and thus equidistantly spaced on a logarithmic scale. Fig. 2 shows the equalization curve obtained when the shunt branch is resonant at F 2 and the series at F 5 . A finer division of the total bandwidth of the network into 16 resonance frequencies may be obtained by the use of a further shunt capacitor 24 of value C/a<SP>2</SP> where C is value of the capacitance 15. The Specification gives a table showing the necessary connections. The bandwidth of the whole network may be extended indefinitely by providing further terminals 12, 13 in the shunt and series branches together with corresponding further adjustable LC networks. A # network can be used instead of a T network.