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#15
June 6th 10, 09:12 PM
posted to rec.radio.amateur.antenna
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BNC connectors 75 Ohm versus 50 Ohm?
Hi Gaius,
Gaius Inscribed thus: In article , says... A 75 ohm BNC plug is identical to a 50 ohm one, save that the male pin in a 75 ohm plug is smaller in diameter. The other way round, a 50 ohm BNC plug will damage a 75 ohm BNC socket. Thats what I said... :-( Sorry. Not so. This is one of the most common urban myths in RF engineering. The pin diameters of BNCs are identical between 50 and 75R. (Measure them !!) I did... :-( The 50R and 75R connectors are mechanically compatible in BOTH directions. Don't take my word for it - check Amphenol's specifications: "Two distinct types of 75ohm BNCs are available, and both mate with each other and with 50ohm BNCs. " I did check that documentation... :-( I've been using 75R and 50R interchangeably for about thirty years, and I've had NO mating damage problems. (Mismatches don't worry me - HF only). I've probably used them for nearer 50 years, and had to replace damaged sockets because the bifurcated female pin had one side broken off. I am aware that some of the early plugs didn't have solidly captive pins and could move forward and cause damage. Greenpar package the plugs/sockets clearly marked 50 or 75 ohm. In all that time I've never bothered to check the specifications until now. Note - type N and type C connectors WILL be damaged if you try to mix 75R and 50R varieties. I suspect this is the source of the BNC myth. Having taken your words and accept that I'm wrong, I can only agree that you're right and it is a myth. Thanks for the insight. Also - some Chinese made BNCs are so badly made that they will damage other connectors - but this is a manufacturing tolerance issue. 73's -- Best Regards: Baron. |
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