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As part of college assignments, I've been asked to explain in detail how certain parameters - informed by the product's manufacturer - of a specific microwave radio system can be measured. Among these parameters, is the receiver's noise figure. Now, I've proposed a measurement diagram like this (from maximintegrated):

Noise figure measurement

Nevertheless, I've been told that this method has a problem, which is that as my DUT is a receiver, it performs demodulation of the microwave input signal and therefore the frequency found at the input of the DUT is different from the one found at the output - I fail to see why this is a problem for this measurement.-

Anyway, the "tip" I was given was to look for the method used by the manufacturer, or the standard applied. Unfortunately, it seems that this information is not provided in the technical description, which I provide below.

Then what I would like to know is how can I overcome this problem of different frequencies at the input/output of the DUT (is it really a problem???) to perform the required measurement.

Link to technical description: Technical description

It's a long document but I believe that the only relevant information in this matter is on page 49, section 8.2.6 "Noise Figure"; and section 7.2 page 39 "Reference Points" which clarifies the points between which the noise figure was measured.

Please note that although I've found related questions to this topic, I could not find any information concerning the frequencies problem I described before.

I will appreciate any help, thanks in advance!

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  • \$\begingroup\$ Companies manufacture broadband random noise sources. Connect one of those to the RF input, and increase the noise until the output SNR drops by 3dB. \$\endgroup\$ – analogsystemsrf Jul 13 '17 at 3:54
  • \$\begingroup\$ And what would my noise figure be then? Is that method described in any document or application note? \$\endgroup\$ – Javi Jul 13 '17 at 5:16
  • \$\begingroup\$ I find the HP/Agilent/Keysight Application notes which describe how to actually measure noise figure much more clear, see: literature.cdn.keysight.com/litweb/pdf/… There are several ways to measure the NF one is using a Noise source which are made by Keysight so they also write App notes how to use these :-) \$\endgroup\$ – Bimpelrekkie Jul 13 '17 at 7:22
  • \$\begingroup\$ That "Noise Figure Analyzer" in your picture also does not reveal how it actually determines the NF which is what your teacher will be asking you to explain !!! Using a noise source and a "standard" spectrum analyzer (without "magic tricks") will teach you how it works and why. \$\endgroup\$ – Bimpelrekkie Jul 13 '17 at 7:29
  • \$\begingroup\$ @Bimpelrekkie thanks, I've already read that app note but as I was not able to find information about that specific problem I mentioned in the post, I didn't event mention it. Anyway, I think I'm going to describe the measurement with the spectrum analyzer as you suggested! \$\endgroup\$ – Javi Jul 13 '17 at 14:19

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