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Setting Highest Source Port Power while maintaining Linearity

Question asked by VNA123 on Jul 9, 2015
Latest reply on Jul 27, 2015 by VNA123

I did a Trace Noise Study between two different VNAs ranging from High (0dB) to Very Low Signal Levels (-100dB) and noticed one had a significantly lower noise floor than the other. This was a controlled experiment. New high quality cables with little movement, stable environment, same connectors. Pretty much, only noise errors and dynamic accuracy errors are playing affect. The "noisier"(loosely used) VNA had a -15dBm source power level (nominal according to spec sheet) where the "better" VNA had a 0dBm source level. Obviously there's a S0/N0 advantage here.

I want to push to Trace Noise on the "noisy"(loosely used) VNA down while maintaining the same if bandwidth and no averaging. So this pretty much means upping the source power of the ports. The goal is to keep testing time low, but have lower trace noise by upping the power.

Right now I'm using the N5245A Option 400 VNA. "Nominal Power" is -15dBm. What does this specifically mean? Receiver Linearity Region? 0.1dB Compression Point? My Ecal unit is N4691B (-5dBm Compression Point According to Spec). I also have 1meter coaxial cables (good quality) that are connecting to the DUT/ECAL (this is where my reference plane is after vector error correction["calibration"]). Like I said, I want to push the source power level higher but keep accuracy and linearity. Can you please provide a way to test this? Or what specs to pay attention to? Is there a procedure in Dr. Joel's Book (my bible)? Obviously, there will always been some factor of non linearity as you go into different frequency bands and optimization is possible, but I must be careful.

I expect that if you know the loss from the Source to the end of the test cable (where your reference plane will be after error correction), the Test Port RX Compression Point, and ECAL Compression Point, can't you theorhetically map out the maximum source power you can set on your VNA without obtaining extra inaccuracies/non-linearities? I do have the VNA Uncertainty Excel Tool FYI (just not sure how to use it properly ;) )

Sorry for the long post. Specifics are important I've learned over the years of forum posting. :)
Please help if you have information available to share.