# Phase Noise Question

Question asked by SOLT_guy on Jan 18, 2013
Latest reply on Jun 15, 2013 by SOLT_guy
Dear Sir:

I would like to have a better understanding of the definition of "single sideband phase noise to carrier ratio per Hz."

I have attached a *.pdf file from a HP Product Note.   Please look at page 5 of this product note.

On page 5, Figure 2.2, there is a graph which is intended to define the term "single sideband phase noise to carrier ratio per Hz" by graphical means through a spectrum analyzer display.    This graph has been utilized in other Agilent/HP seminars to define the term.  The graphical method is the best means to define this term.

However, there is a problem.

If you look at the first plot, the vertical axis is labelled, "A".    I read in other HP literature that this "A" denotes amplitude.   However, the question remains is which "amplitude" is being referenced - power? voltage? etc.).    I don't want to make any assumptions about what the "A" denotes, can you please explicitly tell me what the "A" is intended to denote.

I have a second question and this question references the definition of "single sideband phase noise to carrier ratio per Hz" as defined on page 5.   Page 5 defines "single sideband phase noise to carrier ration per Hz" as:

(power density in one phase modulation sideband) / (total signal power)

In an Agilent document entitled, "Phase Noise Measurement Methods and Techniques", by Kay Gheen (2012):

A nearly identical graph is utilized on page 9 and "single sideband phase noise" is defined as:

(Area of 1 Hz bandwidth) / (Total area under the curve)

I have enclosed a link to the *.pdf file:

My question references the graphical definition of "total signal power" and/or  the "total area under the curve".

If you look at the horizontal axis, one can see that this axis can possibly extend to a near infinite number.   In other words, there is no boundary to the "total area under the curve."

Let's say I had to teach a class to students and I wanted to define the single sideband phase noise using a spectrum analyzer display and I wanted to define what single sideband phase noise is using Agilent's graphical definition set forth on page 5 of its product note.   I want to know where to mark the boundary limits of  "area under the curve" so that my graphical definition is consistent with NIST's defintion of single sideband phase noise.

Can you please show me how to mark, or interpret the graph, so that the graphical definition on page 5 of the Agilent product note is consistent with the definition set forth by NIST?

By the way, in the process of writing this message, I had posted a link to Kay Gheen's *.pdf file and while searching for this link to post to you, I had discovered that this *.pdf file was associated with an Agilent webcast.   I have not seen this webcast yet.  I just found out about it now.   If my answer is found in the webcast, you will know why I did not know the answer to my question.

In any case, can someone please answer my question.  I would like to validate the graphical definition of "the single sideband phase noise to carrier ratio."