Shocking discovery - 75 ohm component cable

[Steve MF Lai]

Many hifi video companies recommend that you use a 75 ohm component cable when connecting DVD component out to TV component in. This cost a fortune - US 100 or more for 1.5m !!!

However, many of the plugs for the component in and out are RCA type. I was told by a friend that you CANNOT get 75 ohms with RCA plugs ! The plugs must be BNC. Hence you are just wasting money if you pay a fortune for a 75 ohm cable with RCA plugs.

Can experts amongst you confirm this please ?

[Phill]

That's complete nonsense. The type of plug makes no difference to the impedence rating of the cable.

Comosite video cables and digital co-ax cables are both examples of 75 Ohm cables terminated with RCA plugs.

You're friend may be confused because RCA audio cables (Phono cables) are 50 Ohm.

[trooper1212]

I've recently bought 3 75Ohm 1.5m leads for £10 each, with phono connectors on each end, so it's definitely rubbish.

T.

[stephen]

The cable will be 75 ohm, but the phono connectors themselves will not be, they will have a different impedance. This will have the effect of reducing the length of cable that can be used, however this will be insignificant at the frequencies and cables involved.

I work for a company desigining broadcast TV equipment, and for HDTV use, the frequencies invloved go up to 1.5GHz and are required to work over distances of about 100 metres, in cases like this it is necessary to use BNC connectors that have impedances matched to the cable, and also to match the impedance of the pcb traces inside the equipment to the cable impedance.

[Steve MF Lai]

Thanks chaps for the assurance - at least I know now the marketing guys out at these companies are selling "the truth".