Circular Waveguide System for Trunk Communications

9-km waveguides of 70-ram inner diameter (ID) have been inserted from manholes into ducts of polyvinal chloride (PVC). Expansion joints are provided for taking up length variations. Only a slight increase in attenuation was measured for the helix waveguide after the laying works. Phase-shift-keyed (PSK) signals with bit rates of up to 640 Mbit/s have been transmitted via this line. A new approximation method for calculating the attenuation of practical line routes has been developed. Improved design of lined waveguides should, from theory, reduce the H
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route and curvature loss to below 1 dB/km. Experimental repeaters work with a double conversion scheme. They have mm-wave branching networks in oversize rectangular waveguide, IMPATT oscillators and p-i-n modulators for two-phase modulation. Printed or folded tape meanderlines serve for delay equalization.