Question How to make out a coaxial digital cable from a RCA

[newlash09]

I have two pairs of hi fidelity RCA's, and one coaxial digital spdif cable. They all look exactly the same 😜😜. And I mixed them all up. Any way I can find out which one is the digital cable. I do have a multimeter at hand. Thanks in advance 🙏

 

[bencat]

Check the ohm reading and provided it is as close to 75 Ohm as possible then that is the correct specification for a digital SPDIF cable . If they are all identical it may well be that they will all measure the same in which case use whichever one you want .

Now the dumb part from me i have never done this so I am not sure how to test this correctly . I would imagine it would a connection from one point on the male pin to the one at the other end , but as I say not totally sure could be from the shield of one end to the pin at the other end . Someone while laughing at my lack of knowledge will be along and tell us all the correct way of doing it and then i will promptly forget it .

 

[awkwardbydesign]

They are probably identical. Many "digital" ICs are simply relabeled.

 

[Paul55]

The characteristic impedance of an S/PDIF cable needs to be in the order of 75R. You cannot reasonably measure this, unless you have an infinite length to work with.

Fortunately the impedance of any normal piece of coax will be about right.

So it's extremely unlikely to matter which cable you use for digital, even if they're somewaht different.

But to be paranoid I would take a look inside the plugs and see if you can spot the odd one out.

FWIW if you're serious about S/PDIF connections you use 75R BNC plugs/sockets. But in practice any phono-phono works.

 

[rabski]

The characteristic impedance of an S/PDIF cable needs to be in the order of 75R. You cannot reasonably measure this, unless you have an infinite length to work with.

Fortunately the impedance of any normal piece of coax will be about right.

So it's extremely unlikely to matter which cable you use for digital, even if they're somewaht different.

But to be paranoid I would take a look inside the plugs and see if you can spot the odd one out.

This.

The 75 ohms for a cable is the characteristic impedance, not the fixed resistance. If you measure the cable with a multimeter, it will tell you nothing other than whether it's broken.

In reality, there is no such thing as a 75 ohm RCA connector, but the closest equivalent should have more air spacing than a standard analogue one. If what you've got all look identical and there are no relevant markings on the cables, it's far from impossible that they actually are all the same.

 

[FunkyMonkey]

If you are able to unscrew the rca plug covers you may see a difference in the coax geometry ,that’s to say the spacing between the centre conductor and screen.