In the past HP/Agilent/Keysight corporation has produced many excellent CD ROM tutorials. The series of CD ROM tutorials were referred to as "Self Paced Tutorials" many years ago.
I was hoping that someone here can direct me to a tutorial of this type, if it exists, that specializes "Vector Signal Generators". Is such a tutorial available?
Dear Mr. Baker;
I would like to thank you for your reply.
The reason why I posed my original question was because there is very little exact "hands
on" information that I could find to help me with a particular problem.
My particular problem is that I am evaluating a vector modulation analyzer (HP 8981A). When I look at the vector diagram and the constellation diagram displays, I see a distinct difference between the two displays when I input a sample RF signal with coherent carrier. When you read historical literature about these two different types of displays, I noticed that some authors have used these two terms interchangeably which has added to my confusion.
I know that HP/Agilent/Keysight has shaped the communications industry with regard to how the industry develops, and, therefore, the definition of the terms that are used in the industry. Maybe, you can help me understand these terms "exactly" and when I mean "exactly", I mean, what do these terms (constellation display and vector display) mean in terms of "hardware" that generates the display that we see.
My question is this:
With regard to all HP/Agilent/Keysight vector modulation analyzers ever made, do all these vector modulation analyzers have a "constellation display" that is based upon the HP 3709B Constellation Analyzer. For your convenience, I will try to upload the HP Journal July 1987 article about the HP 3709B.
If you are having trouble understanding my question, think of this question as analogous to this statement about oscilloscopes.
"All oscilloscopes display the Y-T display in the same manner."
Do all the vector modulation analyzers display the same output when the "constellation" button is depressed and, if the answer to this question is, yes, is this same output, more or less, based upon the hardware design of the HP 3709B?
Also, can you compare and contrast, the vector display and constellation display, and tell me how and why the vector display differs from the constellation display?
Please try to understand the reason why I am posing these fundamental questions is because, over time, industry and textbook, literature have used the terms IQ display, constellation, and vector diagram interchangeably.
I tried to upload the HP Journal July 1987 article but I did not see an "attach" *.pdf button to upload the document.
I believe that you can just google and find this article online. However, for the future of our discussions, if you know how to upload *.pdf files to the webpage, can you please show me how. The old Agilent website discussion forum features were easier to use. This new discussion webpage format uses a lot of symbols and is not very straight forward.
Hi -
In order to include an attachment in a comment you can select "Use advanced editor" in the upper right of the comment box. There you will see a link that says "Attach" which will allow you to attach a pdf to your comment.
Hope that helps!
Thanks, Jill
I can't tell you much about how the forum tools work, I'm new to this one myself. I can't say why you would see a difference between a constellation display and a vector display. In my mind they should be the same. A vector display displays I and Q "values" relative to the ideal in terms of magnitude and phase. A constellation diagram results from looking at a modulated signal, where you see the I and Q values, as well as the path the signal follows between those values. The IQ values (dots) are displayed relative to an internally generated reference, and any offsets in phase or magnitude are shown as phase error or magnitude error, or as a combined error vector magnitude.
A discussion with you about the vector display and the constellation display is going to be difficult because these two display types have been used interchangeably over time. We really don't have a baseline reference, unless we are both looking at a common reference.
Do you own a vector modulation analyzer? I recently acquired a HP 8981A vector modulation analyzer. If you own the same analyzer, or similar test instrument, then we will have a baseline reference.
I look forward to reading your reply.
Unfortunately I couldn't find one in the building. I haven't used one. I usually use either an 89441A or a PSA or MXA analyzer. I did take a look at the 8981A user guide, and it looks like the difference between the constellation display and the vector display is that the constellation display suppresses the display of the signal between time markers. The vector display allows you to see the "path" the signal follows between time markers. There's not much value in looking at that other than being able to see the effects of filtering.
Dear Mr. Baker;
My apologies for my belated reply. I have a tendency to research topics before I reply to them. In this case, I had to purchase a service manual to obtain detailed information.
I took interest in your statement:
"the constellation display suppresses the display of the signal between time markers.."
However, I believe that the terms "vector display" and "constellation display" that you have been using, are the result of using these terms interchangeably historically and may be adding to my confusion. On my HP 8981A I visually see the opposite of what you describe. The constellation display appears to be showing a path and the vector display, more or less, shows "dots" to a greater degree, than the "path."
I believe that we can resolve this confusion by defining how the "suppression of the signal between time markers" is processed. However, before we can approach this topic, we need to discuss a topic that you had mentioned in your first reply, that of the "internally generated reference."
Can you please explain how the internally generated timing reference comes about from this condition:
1) A coherent carrier is connected into the modulation analyzer.
2) A modulated RF signal (QPSK for example) is the secondary input.
The 10 MHz reference is connected to the internal time base (I am mentioning this condition to be complete - one would assume that this had to be connected).
Here's a good description of the measurement process: http://cp.literature.agilent.com/litweb/pdf/5965-2898E.pdf
Dear Mr. Baker;
I would like to thank you for the literature. While I am examining the literature that you linked me to, I would like to know if you can answer a technical question that probably won't be found in any Keysight literature.
Recently, I acquired a HP vector signal analyzer, and I examined the phase of a QPSK signal output from the RF OUT connector (note: the QPSK modulation to the carrier was disabled) and the Coherent Carrier connector, therefore, I was looking at 2 carrier waves. I measured the phase between the 2 signals and discovered that there was fixed phase difference between the two signals (the phase difference may change slightly over time but there exists a definite pattern). I am not certain if my allegedly "calibrated" instrument was, in fact, incorrectly calibrated. Can you tell me if the HP/Agilent/Keysight vector signal generator outputs from these two connector ports are supposed to be 90 degrees out of phase when they are shipped out to the customer?
To answer this question all one needs to do is measure these two outputs with an oscilloscope (the QPSK modulation is disabled).
I look forward to reading your reply.
After examining the circuitry, after the coherent carrier input connector, of the vector signal analyzer, a phase difference from the vector signal generator signal ports would not be necessary. However, I do not make assumptions with regard to test instrument outputs. I look forward to reading an experimental reply from you. A measurement from any vector signal analyzer would probably suffice. If vector signal generator outputs changed over the years and some were manufactured with a 90 degree phase difference between the RF and Coherent Carrier outputs, knowledge of this fact would be helpful - to say the least.
Most signal generators aren't specified for a phase relationship between RF out and coherent out. Coherent out is only specified as not modulated for IQ. There was an option on some generators called "phase coherency", which allows you to shift the phase of the output to match another instrument, but the relationship between RF out and coherent out would remain the same.
Dear Mr. Baker;
Although most signal generators may not explicitly specify a phase relationship between the RF OUT and COHERENT OUT signals in its publications, it does not rule out the possibility that a fixed phase relationship may exist. Please take notice that I am using the term, "possibility" and I would like to look into this "possibility."
Can you please, at least, tell me what you see when you check the phase relationship on your oscilloscope? I would think that you would, at least, be curious. I tend to think any scientist, or engineer, would be curious.
I look forward to reading the results of your test.
I noticed that there conspicuously exists a phase relationship between the coherent carrier and the RF modulated signal when I measure the two signals on my oscilloscope. I used XY mode (lissajous mode) and XT mode on my oscilloscope.
Please use XY mode. The results are very interesting. Please tell me what you see in Lissajous mode.
Note also a change in phase when you enable and disable the modulation button.
There is a fixed relationship between the RF output and coherent out, since the coherent out is coupled off the the same path. The phase shift when turning IQ on is due to the path being switched from the straight-through path to a path through the IQ modualtor. Please take a look at the service guide for your signal generator and look at the block diagram.
Dear Mr. Baker;
I would like to thank you for your past replies and my apologies for a belated reply.
The original topic of discussion for this post concerned software - educational material for vector signal generators. I also started an analogous post for vector signal analyzers and, unfortunately, I did not receive a reply. I am seeking educational software that teach users vector signal generation and vector signal analysis.
As I was searching the web for educational material, I came upon a free software product made by Rhode and Schwarz, named "WinIQsim". I was wondering, does Keysight offer any free software that is similar to "WinIQsim" for its customers?
Again, I would like to thank you for your past replies.
Hello,
I'm not familiar with all the software offered by Keysight. I only use software that interfaces with the signal sources.
There are many application notes covering digital modulation that may help.
http://www.keysight.com/main/facet.jspx?&cc=US&lc=eng&k=digital+modulation&pSearch=tnmSearch&hasLuckySearch=true