[Elecraft] BNCs

[Peter Torry]

Hello Jim,

I quite agree that what matters is that the connector match the physical 
dimensions of the cable.

Originally they didn't mate, 50 Ohm was 50 Ohm and 75 was 75.The pins 
were different diameters, and there were warranty warnings to only use 
the correct connectors with equipment such as the old Tek 475 scope. A 
50 Ohm plug would damage a 75 Ohm socket.

Now modern BNC connectors don't quite make their correct impedance 
characteristics but will physically mate with each other without 
mechanical issue if made to IEC 169-8. The electrical characteristics 
vary between the different impedances and one should be wary of the 93 R 
variety. I understand in the US MIL-STD 348B is similar but doesn't 
state the Zo.Then we have the far eastern manufacturers that appear to 
be slightly different again.

All in all a bit of a nightmare so that was why I suggested being 
careful in selection and using branded connectors from a reputable 
manufacturer.

On the Elecraft front my Def Spec connector doesn't mate correctly with 
the BNC socket on the rear panel of the K3.

I think I had better retire to a dark room.

73

PeterG3SMT


On 13/10/2014 16:45, Jim Brown wrote:
> On Mon,10/13/2014 9:30 AM, Peter Torry wrote:
>> It may not make a difference to performance on HF but it does matter 
>> because the centre pins have different diameters of solder pot / 
>> crimp barrel to match the cable impedance used. 
>
> What matters is that the connector match the physical dimensions of 
> the cable so that it can be properly installed, and this is true 
> regardless of impedance.
>
>> Also incorrectly mated connectors risk damage to their centre 
>> connectors by forcing the engagement.  Use the correct connector for 
>> the cable in use. 
>
> Zo depends upon o.d. of the center conductor with the connectors 
> mated, and would be established by the o.d. of the female pin 
> receptacle, not the o.d. of the male tip. Although I have not studied 
> the mechanical Standard for 75 ohm BNCs, I would VERY surprised if the 
> dimensions of a proper 75 ohm connector would prevent it from mating 
> with a proper 50 ohm connector. Have you studied such a spec?  I'm 
> quite active in international Standards work (with the AES) and that 
> sort of incompatibility is something we make certain to avoid!
>
> 73, Jim K9YC