Re: Measuring Noise Figure


Chris Trask <christrask@...>
 

Thoroughly disagree. I use the 3dB method, which requires a 50-ohm termination, a 3-dB attenuation pad, a noise source, and a means for measuring output noise power (typically a spectrum analyzer). You first measure the amplifier output noise with the 50-ohm termination at the input. Then you add the 3-dB attenuator to the output and the noise source to the input. You adjust the noise source power until the two measurements are the same, then go through some calculations to determine the NF.


I watched a Youtube video recently about measuring noise figure using the measured gain of an amplifier
and a spectrum analyser. The thing that I found odd was that the video maker did not terminate the input
of the amplifier - he said it did not matter. I can think of two reasons why it might matter:

1) the input load resistor provides the base thermal noise level (I suppose it might not matter much if
the amplifier is very noisy)
2) some amplifiers are not entirely stable when un-terminated.

Would you agree?


Chris

When the going gets weird, the weird turn pro
- Hunter S. Thompson

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