GB1272283A - Method for the transmission of information over lines having the character of bandfilters - Google Patents

Abstract

1,272,283. Digital transmission by amplitude, phase, or frequency modulation. MAGYAR TUDOMANYOS AKADEMIA AUTOMATIZALASI KUTATO INTEZET. 21 April, 1969 [24 April, 1968], No. 20308/69. Heading H4P. In a system for use on a line of limited bandwidth e.g. a telephone line, data is coded in conformity with rules such that frequencies of uniform signals have redundant signals inserted which are passed to the line through a filter band passing frequencies e.g. between 300-3400 Hz. At the transmitter a coding unit A receives signals on input 1 from stores, either in parallel form if coding is arranged in blocks, or serially if coding is continuous i.e. on a bit by bit basis. Signals on lead 2 request rest block or bit. The coding output is passed to line M through a band pass filter C e.g. 300-3400 Hz. At the receiver a correction filter and amplifier B suppress disturbances and pass it to a resolver E which reproduces the real and imaginary parts [cos #t and j sin #t] which are passed to an evaluating unit F which reproduces the sequence produced in A and passes it through line 7 to a decoder A<SP>1</SP> which eliminates the redundant bits in accordance with the coding rule. A synchronized clock signal appears on lead 8. If the decoder recognizes an error a signal is returned to a transmitter. Evaluating unit F may sense both phase and relative amplitude of the signals presented to it or such evaluation may be carried out by a digital circuit. For certain types of coding, the latter method may bear similarities to a phase discriminating receiver. In a block coding arrangement described a 5 bit code is converted into an 8 bit code such that the first bit is always "1" and a "0" never follows another "0", a table of such conversions being given in the Specification. Messages and/or blocks may also be headed by synchronizing characters which are recognized by the receiver. In an alternative arrangement decoding is performed on a bit by bit basis instead of in blocks. Other coding rules are envisaged in the specification. It is stated that the equipment will operate at an average speed of 2400 bauds and as an average of 800 redundant bits are produced for 2400 information bits there is a great probability of error recognition. The unit C may incorporate a number of known circuits, e.g. for connection to a telephone set &c. Transmission may be by amplitude, frequency or phase modulation but the received signal will be a sum of sinusoidal signals with different amplitudes and frequencies from which the real and imaginary parts are produced in the resolver. It is considered that the vector of the resolver output is rotating which is recognized by the unit F.