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Measuring OIP3 in 75 ohm environment

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ropt728

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Hi all,

I came through this process with some doubts
If i am measuring OIP3 in 75ohm environment , means there will be two different frequency feed into my input.
Does it cause any unbalanced output ?Do i need a balun to balance it ?:-|
 

I would keep the liine length between the power combiner and the DUT very short. Then I would put at least a 3 dB pad on the two inputs (more is better). You will have some mismatches, but they will be not too big of a problem.

At the DUT output, use a 75 ohm pad once again to keep VSWR standing waves to a minimum.

Of course, you could also use either all 75 ohm components and test gear, or matching 50 to 75 ohm coaxial pads and just take into accout the published loss.
 
What if i setting up my 75 ohm environment with matching pads from 50ohm to 75 ohm, so i still need to use a balun ?
 

I do not understand your question. A balun is not needed to make an OIP3 measurement.

Baluns change single ended to differential signals.
 

If you are referring to a a two port splitter, it depends on your two RF sources and RF levels. Basically you need to prevent one generator from sending significant amount of power back up to other generator. This can set off IM and intermod within the generators. They have ALC circuits for leveling their output so back fed power can upset their ALC and output driver amps.

Most of the time a simple resistive two port splitter will do. A hybrid coupler (power splitter) will improve input port to input port isolation.
 

For a OIP3 measurement, we should be using splitter/combiner right ?
 

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