Vemco VR20 Monitor
The VR20 Monitoring Receiver (1990) replicates the functions of the original UNB Monitoring system pictured earlier and logs information from tagged fish in solid state memory in an underwater housing. The VR20 uses similar technology to the VR60 and scans multiple channels to detect continuous transmitters allowing studies of up to 200 transmitters. Although this was a major step forward as a tool for fish migration studies, it was somewhat large and difficult to deploy in high currents, and was not practical for large arrays. It cost $4500 and the largest array ever deployed was 20 receivers.