Tuesday, March 15, 2011

75 Ohm cable

Joachim's made a post about the use of 75 Ohm cable for ham radio. This is not the first time I see references to this subject but it's the first time I serious think about it.
In a first view I think it should be ok at least for reception or for moderate power transmission beeing impedance match just a small issue. I didn't checked all types of cables and ratings but it's somehow obvious.

This type of cable (75 Ohm) is normally used at TV/Satellite frequencies hence it should be good for HF to VHF and for sure UHF/SHF... but keep in mind that usually there's a mast amplifier or a down converter near the antenna/dish and that makes all the difference. The amplifier compensates attenuation losses and signal to noise ratio degradation!
If we look on the economic side then lets all jump and use 75 Ohm, the price difference it's brutal!
Here's a quick chart on some cables comparation with prices in the local electronics shop.

Now some quick tests with the MFJ antenna "analyser":

Keep in mind that I only used 1m cable length for the tests, I am sure beaviour with bigger cable lengths will be somehow different.

Let me have a little spare time to make some more tests, I have a spare 75 Ohm cable from the shack to the "antenna farm" that will be tested for sure.
For those who live in apartments with some restrictions on antennas it should be easy to justify a white cable going to the roof, just say it's for the satellite dish.

Have fun.


PE4BAS, Bas said...

Interesting, so for the lower frequencies the outcome would be that you can use 75 Ohm TV cable just as well as te expensive 50 Ohm cable. I'll keep that in mind. Thanks for testing 73, Bas

Ricardo - CT2GQV said...

Bas, keep in mind that this test was done with 1 m length cable. Logic/Math tell us that impedance is constant over any cable length but we never know :)