In 1993, Ian Drummond published an article in Speleonics titled Converting Single Sideband CB Radios for use as low frequency cave radios. A PDF scan of his article is here. I was able to obtain a pair of SSB CB radios. I modified Ian's design primarily to improve the dynamic range during receive, then built a pair of Transverters. Later on, some were professionally built and used with "opened up" IC-703 portable ham radios for Thru-The-Earth tests. All of the information that I have on my Transverter design, including a schematic, is here. This is not a full construction article. The original notebook was lost.