An Amphenol document discussing the mating compatibility of their 50-ohm and 75-ohm BNC connectors can be found here _http://www.amphenolrf.com/products/bnc.asp?N=0&sid=46B11E806D75617F_ (http://www.amphenolrf.com/products/bnc.asp?N=0&sid=46B11E806D75617F) . Bruce, KG6OJI