Since you are new to the forum you are probably unaware of how international it is. The reason you got no real response to you query is nobody really understood what the question was.
This is because what I call the CRIMINAL use of acronyms. I am sure somebody can help but we need to know what you mean by DDF so if you would elaborate slightly I am sure somebody would be glad to help.
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An elephant is a mouse built to government specifications.
I suppose you mean DDF = Digital Distribution Frame which is a distribution network technology of digital signals.
75 (or 50 or 60) ohm are controlled impedances when you use coaxial
(or triaxial) = shielded, asymmetrical cables. And unshielded or shielded symmetrical
cables (2 parallel wires) have normally higher impedances of about 2-4
times the above (120, 240, 300 ohm).
In noisy disturbed (or disturbable !!) areas it is recommended to use asymmetrical shielded cables.
You can change between these impedances with so-called "balun-"transformers.
Regards Uwe
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The sum of intelligence on earth is a constant. And the population grows and grows and .....
120 and 75 ohm DDF
Re: 120 and 75 ohm DDF
