Abstract: A pair of full duplex modems are connected and each is designed to transmit to the other at the same predetermined band rates. One modem is connected to receive data bits for transmission over the channel at a predetermined first (and fast) rate and to transmit its received data bits at a integral number of first transmission bits per band. The other modem is connected to receive data bits for transmission over the channel at a rate slower than the band rate and is designed to sequentially encode blocks of said slower rate data bits into a larger number of second transmission bits for transmission over said channel at an integral number of second transmission bits per band. Means forming part of said one modem for converting said second transmission bits into the slower rate data bits.

Abstract: In data transmission data is block encoded into 24 signal values determined by pattern vectors of a Leech matrix, detected and decoded.

Abstract: Numeric signals appearing on a communication channel are converted in blocks of b signals to a number N. The number N is converted to coordinates in K dimensional space where 40.gtoreq.K<4. The coordinates are selected to provide suitable packing in the dimensional space represented by K. The values of coordinates selected are modulated on a carrier and transmitted. Apparatus is provided which carries out the above steps.Where K=24 the coordinates are selected to be expressible in integral form and in integral form are selected so that they have all even values with a sum of 0 modulo 8 or all odd values with a sum of 4 modulo 8.

Abstract: An encoder treats a block of b bits of binary data as a number N and encodes it into eight values S1, S2 . . . S8 identifying it. The eight values are each selected from positive, negative and zero integer values; and the values are chosen so that a set of eight consists of all even integers or all odd integers and so that the sum of the eight values is 0 modulo 4. In the transmitter these values are modulated on a carrier for transmission. A receiver detects the received versions of the transmitted values, determining the number N and reconstituting the block of b bits.

Abstract: A helical resonator filter includes several helical coils, each grounded at one end and free at the other and enclosed within a cavity. The coils are coupled to each other electromagnetically through apertures in the conductive walls separating the resonator cavities from each other. A dielectric member is inserted into the apertures to increase coupling between adjacent coils to increase the bandwidth of the filter.