[time-nuts] BNC question

[Bruce Griffiths]

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
>
There's also the minor issue of 0.7mm and 0.9mm diameter centre pin BNC 
variants.
They do exist, I've seen hundreds of them.

Bruce