A Mechanical Filter Channel Bank

The channel modem is encountered in carrier telephone systems in far greater quantities than any other equipment unit. Measures for improving the productivity with regard to this basic unit of equipment will thus be particularly effective. The newly developed channel modem uses mechanical filters for both the speech channel and the outband signaling. The channel filter has its passband at about 50 kHz and consists of 12 flexural vibrators with longitudinal coupling. Using the premodulation principle, only a single type of channel filter is required. Because of the simple setup of these mechanical filters, they are well-suited for automatic production. An improvement in the electrical characteristics is also achieved. The attenuation distortion in the passband of the loop-connected channel is within 1/10 of the International Telephone and Telegraph Consultative Committee (CCITT) tolerance scheme number 1 without any attenuation equalization. In addition, an essential size reduction has been accomplished. The customary bay volume will accommodate instead of the present 120 channels the channel modems for 600 voice circuits including power and carrier supplies.