[time-nuts] BNC question

[Magnus Danielson]

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