An Experimental Airborne 50-Mc Ionospheric Scatter Communication Circuit

VHF air-ground-air teletype communications by ionospheric scatter propagation have been shown to be feasible. Field strength measurements and baud error data were obtained over a 1500 statute mile flight path across the auroral zone. No degradation of system performance during periods of intense magnetic disturbances was observed; most auroral displays were accompanied by signal enhancement. System performance was evaluated using three orders of frequency diversity and up to six orders of space diversity. Successful teletype operation requires at least two orders of diversity to overcome the severe rapid fading inherent in ionospheric scatter propagation. Synchronous reception was used for the experiment and is recommended for operational systems. An air-ground-air system employing antennas, transmitters and receiving techniques currently available is shown to provide an extremely reliable teletype channel to distances of the order of 1200 statute miles.