What is the relationship between the RU-16, -17, and -18, please. They seem to have some things in common. Best, -John David Stinson wrote: > * In 1932, the stand-alone receiver was designated "RU" and > the receiver/transmitter combination was designated "GF." > GF as a transmitter-only designation happened sometime > between the GF and GF-1. > > 73 Dave S.