Telebyte USA

Micro Line Driver Self Powered model 209FP

A pair of these are required to make a rs-232 long distance extension.

Full duplex.

Data Rates to 19.2K baud

Distances up to 6 miles using low cost 4 wire twisted pair cables.

Retail on these is $79 USA each.

Still a current Telebyte product.

Auction is for a pair

Specs and details

http://www.telebyteusa.com/catalog/products/209.htm