ar-t;348478 Wrote: > Well, you concluded that I was a non-techie, so see what happens when > you draw the wrong conclusion. > OK, I have more time now, so I will try to explain in terms that a > non-native English speaker can understand. > [...] > This odd thing may indeed measure 75 ohms all by itself, > but............. > Once you stick it onto a conventional RCA jack, you now have all that > metal that you went to great lengths to remove back in place. So, it > really isn't 75 ohms once you mate it to a real-world connector. > > Did I address all of your issues?
Great and very clear, thanks! My non-techie remark was probably also the result of my English being 2nd language because I read your post like you were saying toslink was sm glass (the words used) while you obviously meant it was mm plastic and guys using sm glass cables are a joke! ;-) You were hard to follow though because I get quite good in English and don't go that far wrong often. So I apologize for calling you a non-tech; being a tech myself I know it's no fun when that happens. To the point: I follow you now and indeed you addressed my issues. I never did TDR testing of connectors (did for splicing fiber if that's called the same, I can't remember) but spent a lot of time tuning impedances on all sorts of HF circuits and antenna systems. I always assumed buying a good brand connector with the right specs was enough, but I'm starting to question that now. Let me give an example: I bought a professional marine VHF radio. It has a PL-259 50R female chassis-connector on the back. That is physically a big connector, kinda like xlr diameter. I used RG-8U cable and a good plug to connect my antenna system and all is fine, ie. my SWR is 1:1.1 in the center of the band and never goes higher than 1:1.2 at the bands edges. The RG-8U cable is a big coax and indeed matches the connector dimensions roughly (but it's still smaller). However, when I open up the radio and look at the internal connection to the connector there, I see a tiny coax like the size used for wifi radio's. The chassis connector is made to accept the cable because it fits the cable diameter and is crimped on the braid. According to all you wrote, this would lead to a significant impedance mismatch which I didn't measure with the meter because it's beyond the mismatch! It was always (and to be honest, it still is) my understanding that the impact of any mismatch is defined by the physical length of the mismatched section. As the tiny coax is probably 50R again, the mismatch would just be at the point of cable-connection, which is short enough so that it doesn't really impact the transmission line. Now I'm not so sure anymore. I guess I need to find myself a TDR to find out... cheers, Nick. -- DeVerm ------------------------------------------------------------------------ DeVerm's Profile: http://forums.slimdevices.com/member.php?userid=18104 View this thread: http://forums.slimdevices.com/showthread.php?t=52817 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
