50 and 75 ohm BNC Connectors
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I've received a question about compatibility of 50 ohm BNC male
connectors with the 75 ohm female BNC connectors on Exetron's ADA 6 300MX video distribution amplifier. Amphenol makes the following statement about 50 and 75 ohm BNC connectors: "Two distinct types of 75 Ω BNC's are available, and both mate with each other and with 50 Ω BNC's. Type 1 is designated 75 Ω BNC-T1 and provides constant 75 Ω performance with low VSWR DC 4 GHz. Type 2 is designated 75 Ω BNC-T2 and is usable with low reflection DC - 1 GHz. For applications above 1 GHz, Type 1 is recommended. " Unlike BNC connectors, however, please remember that 50 and 75 ohm Type N connectors are not mechanically interchangeable and that physical damage results when a 50 ohm N male connector is inserted into a 75 ohm female N connector. I've added more details on using an ADA 6 300MX to distribute timing signals in today's update. http://www.cliftonlaboratories.com/Updates.htm Jack K8ZOA www.cliftonlaboratories.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: 50 and 75 ohm BNC Connectors
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On Thu, 02 Aug 2007 08:21:10 -0400, Jack Smith wrote:
>Amphenol makes the following statement about 50 and 75 ohm BNC >connectors: Note another very important part of their statement -- that the 50 or 75 ohm impedance of the connector matters ONLY above 1 GHz, and only then in demanding applications. At HF, VHF, and below, the ONLY things that matters are that it fits the cable, it mates with other connectors, is reasonably easy to install, and is mechanically reliable. 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Forgive my ignorance, but what applications above 1 Ghz use 75 ohm
impedances? CATV is the only major 75 ohm application I can think of, and that's 1 Ghz and below. Thanks and 73 Goody K3NG Jim Brown wrote: > > Note another very important part of their statement -- that the 50 or 75 > ohm impedance of the connector matters ONLY above 1 GHz, and only then in > demanding applications. At HF, VHF, and below, the ONLY things that > matters are that it fits the cable, it mates with other connectors, is > reasonably easy to install, and is mechanically reliable. > > > -- Blog: http://thek3ngreport.blogspot.com/ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: 50 and 75 ohm BNC Connectors
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My DirecTV HD receiver uses (i.f.) frequencies up to 2150 MHz. Some
stacked TV distribution systems (multiple-dwelling units) go up to 3 GHz. Of course, these don't use BNCs. 73, Bob N7XY On Aug 2, 2007, at 8:22 AM, Goody K3NG wrote: > Forgive my ignorance, but what applications above 1 Ghz use 75 ohm > impedances? CATV is the only major 75 ohm application I can think > of, and that's 1 Ghz and below. > > Thanks and 73 > Goody > K3NG > > Jim Brown wrote: >> >> Note another very important part of their statement -- that the 50 >> or 75 ohm impedance of the connector matters ONLY above 1 GHz, and >> only then in demanding applications. At HF, VHF, and below, the >> ONLY things that matters are that it fits the cable, it mates with >> other connectors, is reasonably easy to install, and is >> mechanically reliable. >> >> > > > -- > Blog: http://thek3ngreport.blogspot.com/ > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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RE: 50 and 75 ohm BNC Connectors
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In reply to this post by Jack Smith-6
While not an RF application. 75 ohm connector BNC and others are important
to the digital video production environment. It is my understanding that a 50 ohm barrel at the end of the correct length of coax will stop a digital video signal. I am in the process of installing a new digital switcher and I am watching connector, barrels, terminators impedances closely. Rick Kent WD8AJG K2 5296 -----Original Message----- I've received a question about compatibility of 50 ohm BNC male connectors with the 75 ohm female BNC connectors on Exetron's ADA 6 300MX video distribution amplifier. Amphenol makes the following statement about 50 and 75 ohm BNC connectors: "Two distinct types of 75 O BNC's are available, and both mate with each other and with 50 O BNC's. Type 1 is designated 75 O BNC-T1 and provides constant 75 O performance with low VSWR DC 4 GHz. Type 2 is designated 75 O BNC-T2 and is usable with low reflection DC - 1 GHz. For applications above 1 GHz, Type 1 is recommended. " Unlike BNC connectors, however, please remember that 50 and 75 ohm Type N connectors are not mechanically interchangeable and that physical damage results when a 50 ohm N male connector is inserted into a 75 ohm female N connector. I've added more details on using an ADA 6 300MX to distribute timing signals in today's update. http://www.cliftonlaboratories.com/Updates.htm Jack K8ZOA www.cliftonlaboratories.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: 50 and 75 ohm BNC Connectors
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Richard:
I would be amazed if a single 50 ohm barrel would "stop" a digital video signal. A high bit rate digital waveform, such as digital video, is subject to destructive interference due to reflected signals--if the bit rate is sufficiently high and the rise/fall time sufficiently short, and if the noise margin of the signal is sufficiently low for reflected signals to cause bit errors. I really doubt that a single 50 ohm connector, however, would cause a major problem. There's a much larger problem with high frequency attenuation in sending data over coaxial cable, which is normally fixed via equalizers and regenerators in the telecom world. That's one reason fiber has proven to be desirable even for relatively low bit rates. There's a lot of "ifs" in that statement, but still if I were building a video plant with 75 ohm coaxial cable and 75 ohm equipment, I would certainly use 75 ohm BNC connectors to reduce reflections and because they fit 75 ohm cable mechanically. When distributing a 10 MHz reference sine wave over 50 feet, however, the impedance bumps from mixing 50 and 75 ohm impedances do not prove to be a significant issue. In fact, I could probably use 50 feet of zip cord connected via alligator clips to distribute timing signals if I had to. (My measurements on zip cord show it to have an impedance around 100-125 ohms but to be on the lossy side.) Jack K8ZOA _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: 50 and 75 ohm BNC Connectors
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The reason it *might* stop the signal is that a 75 ohm center pin
would not necessarily make contact with the 50 ohm center contact of the barrel. The diameter is quite a bit smaller in order to achieve 75 ohm impedance. Likewise, a 50 ohm center pin could damage a 75 ohm receptacle. Bob, N7XY On Aug 6, 2007, at 10:46 AM, Jack Smith wrote: > Richard: > > I would be amazed if a single 50 ohm barrel would "stop" a digital > video signal. > A high bit rate digital waveform, such as digital video, is subject > to destructive interference due to reflected signals--if the bit > rate is sufficiently high and the rise/fall time sufficiently > short, and if the noise margin of the signal is sufficiently low > for reflected signals to cause bit errors. I really doubt that a > single 50 ohm connector, however, would cause a major problem. > There's a much larger problem with high frequency attenuation in > sending data over coaxial cable, which is normally fixed via > equalizers and regenerators in the telecom world. That's one reason > fiber has proven to be desirable even for relatively low bit rates. > > There's a lot of "ifs" in that statement, but still if I were > building a video plant with 75 ohm coaxial cable and 75 ohm > equipment, I would certainly use 75 ohm BNC connectors to reduce > reflections and because they fit 75 ohm cable mechanically. > > When distributing a 10 MHz reference sine wave over 50 feet, > however, the impedance bumps from mixing 50 and 75 ohm impedances > do not prove to be a significant issue. In fact, I could probably > use 50 feet of zip cord connected via alligator clips to distribute > timing signals if I had to. (My measurements on zip cord show it to > have an impedance around 100-125 ohms but to be on the lossy side.) > > Jack K8ZOA > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: 50 and 75 ohm BNC Connectors
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In reply to this post by Jack Smith-6
On Mon, 06 Aug 2007 13:46:21 -0400, Jack Smith wrote:
>I would be amazed if a single 50 ohm barrel would "stop" a digital video >signal. This IS way off topic, but the right answer lies in studying reflections and losses. Any real world video cable will have significant loss in the GHz range, so reflections are unlikely to travel very far from one termination to another and still be strong at the other end. In other words, lets say you had two video monitors on a line, one at the end, terminated, and the other bridging somewhere along the line. The bridging one would see reflections from a mis-match at the end monitor, attenuated by the loss in the line between the two monitors at the frequency at which the mismatch was significant (>500 MHz), and the monitor at the end of the line would NOT see its own mismatch. And I'm talking small mismatches here -- a 50 ohm connector instead of a 75 ohm one, not a MISSING 75 ohm term, or a double one. And a double term would be far less problematic than a missing one. In his EMC lectures, Henry Ott correctly observes that a mismatch produces a reflection that is observable only at a distance from the mismatch, not at the point of a mismatch. So if I were building a precision video or data plant that might need to work well into the hundreds of MHz range, I would be pretty careful about connector impedance at passive patch points, but not at terminations. And the input of an ACTIVE router is a termination! 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: 50 and 75 ohm BNC Connectors
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In reply to this post by Bob Nielsen-2
Bob:
No... at least according to Amphenol, who makes the connectors, the mating end of the center pins are identical diameter in both the 50 and 75 ohm BNC versions and are mechanically interchangeable. Not so with Type N connectors, where the pins are different diameters and can cause the problems you mention. Jack K8ZOA Bob Nielsen wrote: > The reason it *might* stop the signal is that a 75 ohm center pin > would not necessarily make contact with the 50 ohm center contact of > the barrel. The diameter is quite a bit smaller in order to achieve > 75 ohm impedance. Likewise, a 50 ohm center pin could damage a 75 ohm > receptacle. > > Bob, N7XY > > On Aug 6, 2007, at 10:46 AM, Jack Smith wrote: > >> Richard: >> >> I would be amazed if a single 50 ohm barrel would "stop" a digital >> video signal. >> A high bit rate digital waveform, such as digital video, is subject >> to destructive interference due to reflected signals--if the bit rate >> is sufficiently high and the rise/fall time sufficiently short, and >> if the noise margin of the signal is sufficiently low for reflected >> signals to cause bit errors. I really doubt that a single 50 ohm >> connector, however, would cause a major problem. There's a much >> larger problem with high frequency attenuation in sending data over >> coaxial cable, which is normally fixed via equalizers and >> regenerators in the telecom world. That's one reason fiber has proven >> to be desirable even for relatively low bit rates. >> >> There's a lot of "ifs" in that statement, but still if I were >> building a video plant with 75 ohm coaxial cable and 75 ohm >> equipment, I would certainly use 75 ohm BNC connectors to reduce >> reflections and because they fit 75 ohm cable mechanically. >> >> When distributing a 10 MHz reference sine wave over 50 feet, however, >> the impedance bumps from mixing 50 and 75 ohm impedances do not prove >> to be a significant issue. In fact, I could probably use 50 feet of >> zip cord connected via alligator clips to distribute timing signals >> if I had to. (My measurements on zip cord show it to have an >> impedance around 100-125 ohms but to be on the lossy side.) >> >> Jack K8ZOA >> >> >> _______________________________________________ >> Elecraft mailing list >> Post to: [hidden email] >> You must be a subscriber to post to the list. >> Subscriber Info (Addr. Change, sub, unsub etc.): >> http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/subscribers.htm >> Elecraft web page: http://www.elecraft.com >> > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: 50 and 75 ohm BNC Connectors
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In reply to this post by Richard Kent
50 and 75 ohm BNC connectors fit each other fine differing only in the
dielectric and width in the crimping area. The mating areas are the same or so the makes of the connectors say. As for the impedance bump, I would not worry about it one bit at video analog frequencies unless the cables were of tremendous length. If the video signal gets stopped something else is terrible wrong. John Richard Kent wrote: >While not an RF application. 75 ohm connector BNC and others are important >to the digital video production environment. It is my understanding that a >50 ohm barrel at the end of the correct length of coax will stop a digital >video signal. I am in the process of installing a new digital switcher and I >am watching connector, barrels, terminators impedances closely. > >Rick Kent >WD8AJG K2 5296 > >-----Original Message----- > >I've received a question about compatibility of 50 ohm BNC male >connectors with the 75 ohm female BNC connectors on Exetron's ADA 6 >300MX video distribution amplifier. > >Amphenol makes the following statement about 50 and 75 ohm BNC connectors: > >"Two distinct types of 75 O BNC's are available, and both mate with each >other and with 50 O BNC's. Type 1 is designated 75 O BNC-T1 and provides >constant 75 O performance with low VSWR DC 4 GHz. Type 2 is designated >75 O BNC-T2 and is usable with low reflection DC - 1 GHz. For >applications above 1 GHz, Type 1 is recommended. " > >Unlike BNC connectors, however, please remember that 50 and 75 ohm Type >N connectors are not mechanically interchangeable and that physical >damage results when a 50 ohm N male connector is inserted into a 75 ohm >female N connector. > >I've added more details on using an ADA 6 300MX to distribute timing >signals in today's update. http://www.cliftonlaboratories.com/Updates.htm > >Jack K8ZOA >www.cliftonlaboratories.com > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com > > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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