COMET - A New Meteor-Burst System Incorporating ARQ and Diversity Reception

A system has been built to make efficient use of meteor-trail reflections for telegraph communications in the VHF band over distances up to 2000 kin. The information is transmitted over the circuit in both directions at an instantaneous rate of 2000 bauds whenever a radio path is established by reflection from a meteor trail. The control of the flow of information is not based on an assessment of the signal strength, as for instance in the JANET system, but on an error-detection scheme with automatic request (ARQ). This technique makes it possible to minimize starting delays and to carry on transmission until the end of the signal burst independently of the rate of decay. A special synchronization procedure has been developed to enable the system to cope with path length variations up to one character in length. The system also features frequency, space, and height diversity. For more than a year extensive measurements were carried out on a 1000-km path at frequencies in the 36- to 39-MHz band. The transmitter power was 200 watts and the antennas were five-element Yagis. Hourly average values of the traffic capacity were found to vary between four to eight 50-baud channels in the early morning and between one half to two channels in the late afternoon with the average over 24 hours approximately three channels. The error rate was less than one in 3000 characters for 90 percent of the time. Statistical data concerning bursts, interval between bursts, and delays in the transmission of messages are presented.