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bk T
16-04-2010, 11:38 AM
I've got a length of 50 Ohms coaxial cable, can I use it to connect my laptop's tv output to my TV set? I know I need a 75 Ohms coax cable but haven't got one at the moment. Are they inter-changeable?

R2x1
16-04-2010, 12:34 PM
Not really.
When you use the wrong impedance cable it is likely to behave as a transformer, with interesting results if you get the length wrong. It won't do any harm, but it may be unlikely to do much good either unless the length is just right, this is not too simply achieved in practise

Billy T
16-04-2010, 06:27 PM
Not really.
When you use the wrong impedance cable it is likely to behave as a transformer, with interesting results if you get the length wrong. It won't do any harm, but it may be unlikely to do much good either unless the length is just right, this is not too simply achieved in practise

Suck it and see, your computer's impedance matching will not be that flash anyway, and once you get over a few wavelengths long the cable will be OK. It is not ideal, but at receiving power levels I'd try it before I spent money on 75 ohm. It doesn't have to be a precise length as suggested above, in fact technically it should avoid being a precise multiple or sub-multiple of the receiving wavelength as that can cause a signal null at the receiver termination.

Many years ago in the days of TV1, 2, 3 and that's your lot, and in another life, I was looking at a signal reception problem in a customer's home and their TV2 reception was awful while 1 & 3 were fine. Clearly their antenna was not the problem, so I cut about 500mm off the antenna lead at the set end, re-terminated it, and TV 2 was perfect. It was a tuned length with the signal null appearing precisely at the tuner input on TV2's frequency.

Cheers

Billy 8-{)

porkster
16-04-2010, 07:01 PM
It will be fine, 50 ohms coax is 50 ohms only if terminated in 50 ohms (or infinitively long).
The result may be a little attenuation of signal but the signal level output from your laptop and the AGC in your TV will easily compensate for that.