There seems to be confusion over 50/75 ohm connector mechanical compatibility.
50 and 75 ohm N connectors are not mechanically compatible as the center pins are different diameter--50 ohm has larger pin diameter. Over time, a 50 ohm N male connector can damage the 50 ohm female N and a 75 ohm N male may not make reliable contact with the 75 ohm female N. However, everything I can find in terms of published dimensions, specifications and measured diameters says that BNC pins are of identical diameter in 50 and 75 ohm variants. The difference in impedance seems to be handled in the dielectric dimensions and material. Many HP 75 ohm BNC connectors, for example, have no plastic dielectric at all in the female version--the center socket fingers have nothing supporting them but air. It may be that in "ye olde days" of the early 1940's when the BNC was invented pin diameters differed, but if that was the case then, it seems to have vanished in the last few decades. Jack K8ZOA On 9/17/2012 4:19 AM, David Cutter wrote: > Wrong use of 75/50 ohm cables is a cause of unreliability on scopes: they're > made for 75ohm connectors and if you plug in a 50ohm plug is will eventually > splay the centre contact and cause intermittency. > > David > G3UNA > > Subject: Re: [Elecraft] [K3] [P3] IF Out / IF In Cable > > >> Yes, the cable impedance does not matter but the connectors do. The >> 75-ohm cable probably has 75-ohm BNC plugs, which as I recall have a >> smaller pin. They might not make reliable connections with the 50-ohm >> sockets on the K3 and P3. >> >> Go ahead and try it, but if the connections seem flakey you should get a >> real 50-ohm cable. >> >> Alan N1AL >> >> >> On Sat, 2012-09-15 at 17:21 -0700, Jim Brown wrote: >>> On 9/15/2012 5:01 PM, Vic K2VCO wrote: >>>> Just try one of the non-50-ohm cables and see if it works >>> Cable impedance absolutely does not matter for such a short run at the >>> IF frequency. >>> >>> 73, Jim K9YC >>> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
