The Canadian geophysical long baseline interferometer

The Canadian geophysical long baseline interferometer, a new very long baseline interferometer system, has been developed and put into operation. The system tracks source delay and fringe rotation during observation using a wave front clock. After the low-noise receiver the signals from radio sources are channelized and down converted to baseband, each baseband channel is one bit digitized at a rate of 12 mbar/s and then recorded on a single video cassette recorder for processing. The total bandwidth of the system can be easily increased by replication of baseband channels. During processing the tapes are played back in synchronism and the recovered astronomy data are processed in a simple correlator to obtain the source visibility. The use of wave front clock allows bursts of wideband astronomy data to be sampled at a high rate at each station and then recorded at a lower rate for processing. Because bursts recorded at different stations at the same wave front clock epoch are emitted by the source at the same time, they are correlated. The fringe visibility obtained from processing the bursts would provide high-delay resolution geodetic measurements commensurate with the wide bandwidth of the bursts.