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Train PBRVY rounds the big curve at Caliente on October 31, 1976. The SP began experimenting with radio controlled helpers during the summer of 1974. The railroad received a small group of Tunnel Motors equipped with the special transmitters and receivers. Units in the 8300 series were equipped to be masters and units in the 8350 series were set up as slaves. Initial tests on the steep grades of Tehachapi were not very successful due to tunnels and mountains that blocked radio transmissions. In early 1976 SP borrowed BN SD40-2s 6800 thru 6807 (masters) and RCUs 105 thru 112 (F7 B units with receivers to control slave units). By 1977 the BN units had been returned and the SP units shifted to the Sunset Route which had no tunnels but enough ups and downs to make radio helpers quite useful. Disk 41