SDI vs Analogue Cable

[paulears]

I've been looking at my collection of cables and the common factor is that all my 50 Ohm cables have a constant diameter centre pin with a rounded end, and all the 75Ohm types I have, have a thinner end on them. I must admit to being confused now. Some of these leads are with properly fitted connectors supplied by decent firms and others are moulded, but they look different, and I've always been able to sort them quickly. I read years ago that inter series mating didn't cause the failures some people talked about, and I've never had any issues having to use the wrong one. As soon as SDI came out the doom and gloom warnings had me buying pre-made cables. Looks like some real confusion now. At least, in my head, trying to forget what I assumed was correct!

[abbotsmike]

I don't think I can offer any clarity but:

 

I have a few SDI cables near me. The cheap ones all seem to use "50 ohm" BNC connectors with the extra PTFE dielectric. These are video cables made with URM70 and RG59. Pin diameter is .032" at the tip, but does widen. The more expensive ones (that I made) are true 75 ohm BNC connectors, and don't have the extra PTFE dielectric.

 

 

 

 

Cable Connector PTFE Insert? Pin Dia Notes

Bryant SD03 Bryant 55C3G No 0.048", Looks straight sided "Proper" 75ohm video cable, assembled by me

URM70 Unknown Yes 0.032", gets wider Preassembled cable, source unknown

RG59 Unknown Yes 0.055", looks straight sided Preassembled pro signal video cable

The URM70 ones seem pretty decent. The RG59 ones do seem to cause poor connections in time, looking at it I suspect the oversized pin is why. In isolation they're good for about 50m on a 3G-SDI use case

[paulears]

I've never found any 50Ohm connectors a proper fit with 75Ohm cable. The sizes of everything just don't seem to work for me?

[pete10uk]

So I've asked a few people about this and I've received a response by proxy from someone quite high-up in a company which wires studios and OB trucks for the likes of the BBC and other broadcasters.

There is absolutely no difference in the mating surfaces of BNC's used for Analog or SDI, the only differences are at the cable input side to allow different cables specs.

 

I didn't get any information on any differences between the different ohm connectors but as I think video is all 75ohm that shouldn’t matter. I think I recall old coax network cable being different, but that should be well out of circulation by now!