Types

> > Types > > BNC connectors exist in 50 and 75ohm > <http://en.wikipedia.org/wiki/Ohm>versions, matched for use with > cables of the samecharacteristic impedance > <http://en.wikipedia.org/wiki/Characteristic_impedance>. The 75 ohm > types can sometimes be recognized by the reduced or absentdielectric > <http://en.wikipedia.org/wiki/Dielectric>in the mating ends. The 50 > and 75 ohm connectors are typically specified for use at frequencies > up to 4 and 2 GHz respectively. > > 75 ohm BNC Connectors are primarily used for video andDS3 > <http://en.wikipedia.org/wiki/Digital_Signal_3>Telco central office > applications^[/clarification needed > <http://en.wikipedia.org/wiki/Wikipedia:Please_clarify>/] , whereas 50 > ohm are used for data and RF. TheBBC > <http://en.wikipedia.org/wiki/British_Broadcasting_Corporation>had a > convention that BNC connectors used for video were always 50 ohm, > maybe because an accidentally connected 50 ohm plug would damage a 75 > ohm socket.^[/dubious > <http://en.wikipedia.org/wiki/Wikipedia:Disputed_statement>--discuss > <http://en.wikipedia.org/wiki/Talk:BNC_connector#Video>/] Many VHF > receivers used 75 ohmantenna > <http://en.wikipedia.org/wiki/Antenna_%28radio%29>inputs, so they > often used 75 ohm BNC connectors. > I had remembered that it was a 75 ohm that would damage a 50 ohm socket. This article states that a 50 ohm would damage a 75 ohm socket. Greg On 4/10/2011 9:25 AM, Greg Broburg wrote: > From what I recall from our candle lit lab, the 75 ohm > BNCs had a slightly larger pin and would open up the > 50 ohm females just a skoosh so when you put a > 50 ohm, into a 50 ohm that had been tweaked by a > 75 ohm, they were noisy or intermittent. > > Greg > > On 4/10/2011 5:30 AM, Magnus Danielson wrote: >> On 04/10/2011 01:51 AM, Mike S wrote: >>> At 06:53 PM 4/9/2011, Joseph Gray wrote... >>>> I have an old Arcnet hub that I want to salvage the isolated BNC >>>> connectors from. Arcnet used 93 Ohm coax. I know that there are 50 Ohm >>>> and 75 Ohm versions of BNC connectors, but the ones from the hub look >>>> like a 50 Ohm BNC to me. >>> >>> The ARCNET spec states: "The MIC for use with coaxial cable is a >>> conventional BNC per MIL-STD-348A." If you look at that spec, it's for >>> 50 Ohm connectors. 75 Ohm ones don't have the insulator around the >>> center socket. Since ARCNET only ran at 2.5 MHz, the mismatch >>> apparently >>> didn't matter. >> >> Risetime is the key aspect. If the impedance missmatch is >> sufficiently small compared to the rise-time, it has no significant >> effect. >> >> As I recall it ARCNET wasn't running at very high speeds and hence no >> need for short rise-times. >> >> Cheers, >> Magnus >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

Greg Broburg wrote: >> receivers used 75 ohmantenna >> <http://en.wikipedia.org/wiki/Antenna_%28radio%29>inputs, so they >> often used 75 ohm BNC connectors. >> > > I had remembered that it was a 75 ohm that would damage a > 50 ohm socket. This article states that a 50 ohm would > damage a 75 ohm socket. > > Greg Sadly, you remembered incorrectly. Both 75 ohm, and 50 ohm BNC parts use the same center pin assemblies. The only difference is the 75 ohm part has the teflon shroud removed from around the female pin. They mate in all combinations without any risk of damage. The N style connector is a different story, however. It is a higher performance connector, and as a result they needed to make the center conductor of a 75 ohm connector smaller in diameter all the way through, so the 75 ohm center male pin is slender, as is the 75 ohm center female pin. If you jam a thicker 50 ohm center pin into the slender 75 ohm female pin, it will bend the socket leafs out and probably break it. -Chuck Harris

Chuck Harris wrote: > Greg Broburg wrote: > >>> receivers used 75 ohmantenna >>> <http://en.wikipedia.org/wiki/Antenna_%28radio%29>inputs, so they >>> often used 75 ohm BNC connectors. >>> >> >> I had remembered that it was a 75 ohm that would damage a >> 50 ohm socket. This article states that a 50 ohm would >> damage a 75 ohm socket. >> >> Greg > > Sadly, you remembered incorrectly. Both 75 ohm, and 50 ohm > BNC parts use the same center pin assemblies. The only > difference is the 75 ohm part has the teflon shroud removed > from around the female pin. They mate in all combinations > without any risk of damage. Not necessarily true, BNCs intended for use with RG59 cable with either a 0.7mm diameter pin or a 0.9mm diameter pin are readily available. Whilst one of these may now be non standard they are nevertheless they are still available from Chinese manufacturers at least. > > The N style connector is a different story, however. It is > a higher performance connector, and as a result they needed > to make the center conductor of a 75 ohm connector smaller > in diameter all the way through, so the 75 ohm center male > pin is slender, as is the 75 ohm center female pin. If you > jam a thicker 50 ohm center pin into the slender 75 ohm > female pin, it will bend the socket leafs out and probably > break it. > > -Chuck Harris > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

Thanks for all the input. I looked closely at the connectors and they seem to match some 50 Ohm connectors that I have. I have removed them from the board and now have eight isolated BNC connectors for my project. Joe Gray W5JG