Spectrum Analyzers Step by Step (029c)
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- เผยแพร่เมื่อ 24 ธ.ค. 2024
- How do I use a Spectrum Analyzer?
In this video I will be stepping through he process of how to get ready to use and how to use a Spectrum Analyzer.
You must answer 5 questions in preparation for your measurement. I will discuss how to answer these questions.
I will explain
How to set up the frequency limits
Adjust the RBW and VBW
Use markers
As part of this who process, I will also explain what dBm is and how to convert from and to dBm.
**** IMPORTANT NOTE: ****
The difference between signal levels MUST be expressed in dB, NOT dBm.
A +20 dBm signal is 0.1 Watts; a +10 dBm signal is 0.01 Watts. If I subtract 10 dBm from the +20 dBm signal, I get a 0.09 Watt signal which is +19.54 dBm.
*****---------------------------------*****
In this series:
VIDEO #1: What a Spectrum Analyzer does.
VIDEO #2: How it does what it does.
VIDEO #3: Spectrum Analyzers Step-by-Step, a "How to" video.
HERE IS THE LINK TO THE PDF:
drive.google.c...
For more information, you can read this very complete book:
"Fundamentals of Spectrum Analysis" by Christoph Rauscher; (c) Rohde & Schwarz GmbH & Co KG, 2014; www.rohde-schwarz.com
Time Markers for Your Convenience
----------------------------
00:05 Introductory Comments
01:15 The List of Pre-Measurement Questions
01:48 DEMO #1: A Signal and its Harmonics
01:52 Question #1: What am I trying to do?
03:26 Question #2: What are the Frequencies associated with the measurement?
05:13 Question #3: What is the Amplitude of the source?
05:20 Converting to dBm
08:44 Relate this to our Spectrum Analyzer
09:19 Converting from dBm
11:50 Question #4: What is the Impedance of our Source?
12:32 Simple fix
13:59 The BEST fix
14:45 Question #5: What is the D.C. Offset of my source?
16:28 How to deal with too much D.C. Offset
18:10 On the Bench with our Demonstration
19:01 Explaining RBW and VBW
21:51 Introducing Markers
22:52 Finding a Transient Signal: MAX Hold
24:15 DEMO #2: FM Sidebands
24:21 Answering our 5 questions.
25:49 On the bench
26:50 Adjusting the RBW
27:49 Final Comments and toodle-oots
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I just finished watching 029a, b and c. I find these videos to be highly informative and educational. It’s really nice to have these things explained by someone who really knows what he’s talking about. Thank you very much for your efforts in creating and uploading these videos.
You are very welcome! I am soooo glad that you are finding them to be just what you need! 🙂 Thank you for letting me know! 😃
This is the first spectrum analyzer video which I've watched that firstly takes you through the key base mathematical information required and understandings prior to using an instrument. Thanks Ralph for answering and confirming so many concerns that I've had in using my little Rigol SA. 73 de GI8WFA.
Thank you! and ... you are very welcome! 🙂
Cool. My daughters 13 and 16 have a Tiny SA ultra, but they are getting a Siglent for christmas. Going to try and use this series for them to experiment with it.
WOW! Now that is **COOL**! 🙂
Excellent tutorial Ralph. Your use of graphics accompanying the presentation were superb. You put a lot of time into these videos and I'm sure viewers appreciate your efforts. Another trick when measuring harmonics is using a notch filter at the input of the SA to reduce the fundamental. This reduces harmonics generated in the SA due to intermod. I get nervous when probing a device as it is easy to probe where no SA should go. Using a pick up made from a short length of coax with a small coupling loop on the end can prevent a disaster . I made one with the barrel of an old bic pen as a handle and it really helps safely sniffing through a device. Looking forward to the next one. 73
Glad you liked it, Todd.
Came for knowledge and found wisdom 🙏🙏🙏
Thank you so much! 🙂
Thank you Ralph!
You do such great work making the complex subjects (somewhat 🙄) easy.
I have used my $11k Agilent portable SA with TG (purchased before discovering Rigol) for a single solitary task…
Tuning duplexers, cavities and filters for 2-way radio gear.
I am fairly clueless when it comes to the more complex test gear, so your videos are quite informative.
Thanks Again.
🙂
You are very welcome ... and thank you! 🙂
In my experience, mobile duplexers only need to have the reject frequency tuned. An SA with TG is sufficient and does a good job.
With larger duplexers, such as what are used in repeaters, you have to tune both the pass band return loss and the reject frequency. This requires a bit more equipment; this cannot be done with just an SA.
I have some videos on tuning those beasts, if you are interested. The *real* beasts are the hybrid-ring duplexers - a video all on its own including the theory behind how they work.
Anyway, I am glad you enjoyed the video! 🙂
Wow really great videos Ralph thanks.
Thanks, man! :-)
This is a great video. Thank you. I will learn a great deal from this.
Thanks, man! :-)
Well explained. Thank you.
Thank you ... and you are welcome! 🙂
Thanks for the amazing content! It helped me a lot!
You are very welcome! If there is stuff you'd like to see, let me know! 🙂
SUBSCRIBED !!!
Very good video. Thanks so much for going to the time and trouble.
73... 😀
You are very welcome! And, welcome to the Inquisitive Experimenter "Family." :-)
great video!
Thanks, man! 🙂
Nice video, well done. One little detail: the difference between two dBm-levels is expressed in dB, not in dBm
Yes, you are absolutely correct!
A 20 dBm signal is 0.1 Watts.
A 10 dBm signal is 0.01 Watts.
If I subtract 10 dBm from a 20 dBm signal, I get a 0.09 watt signal => 19.542 dBm ... NOT 10 dBm! Good catch!
I will add this to the description for the video.
@@eie_for_you As you showed clearly in your example it is not only a matter of taking care with the "units" (I'd call them pseudo-units) but also of the involved numerical values. For that reason I am bit reluctant using the words "adding" or "subtracting" when dealing with dBm's, because strictly mathematically the result of that operation should be expressed in dBs. I prefer the word "combining" dBm's in stead of "adding" and to make the matter even a bit more interesting: depending on the correlation between the powers you are combining the result will be different. Kind regards.
Classic and useful
Thank you! I am so glad it was helpful! 🙂
THX.
You are very welcome! 🙂
Thank you.
You are very welcome! 🙂
I always used the definition that 0 dBm = 1 mW @ 600 ohms (0.775 V), for audio, and for RF, the reference level being either the input or output of the circuit. Is that "0 dBm = 1 mW @ 50 ohms" the accepted standard for RF?
Well, as I understand it, it is 0 dBm = 1 mW @ the characteristic impedance of the system, which, as a general rule, is 50 Ohms. But, there are 75 Ohm systems among others.
@@eie_for_you That would make sense, that it's always 1 mW, for whatever the Z is.
Zero dBm is ALWAYS one milliwatt, regardless of the impedance.
What does change, of course, is the VOLTAGE that corresponds to one milliwatt of power for the different impedances. E.g., for 50 ohms, 0 dBm corresponds to 0.2236068 volts, while for 600 ohms, 0 dBm corresponds to 0.77459667 volts.
One more thing: if 0 dBm is AVERAGE power, then the two voltages cited above are RMS voltages.
@@manfredcaranci6234 Yes, the "m" indicates "milliwatt." But when I see "dBm," I usually think of 600 Ohms & 0.775 V audio, since that's how I most often encountered in (in broadcasting). I rarely encountered it with RF, aside from switching the attenuator og an RF generator.
Nice
Thanks, man! :-)
Thank wonderfool rxplication
You are very welcome! 🙂
Gday Ralph. Im inquisitive!
Can you measure SSB PEP with a SA? Can the average at the peak of an envelope be captured? I dont have an Oscilloscope for this but I do have a RSP1A with the free SA software. Goes down to 1hz RBW. Has peak of the average function and peak markers.
I have seen many videos and instruction of CW power measured on SA but never SSB PEP. Makes me believe it cannot be done with the SA, but would love to be wrong.
I Need to build my stepped attenuator kit to have a go myself ,but I have been advised wisely that 40db is probably pushing it fine with 10w into the SA with max recommended 0dbm input.
So Im going to get a larger 50db att before experimenting. ATTENUATE!
Well, good morning to you! 🙂
So, it is all your fault. I went out and ordered an RSP1B! LOL! 😀 Please send me a link to the Free SA software.
I had tried a different SDR before and was somewhat underwhelmed. Hopefully, this one will be more impressive.
Yes, I *strongly* advise the 50 dB attenuator. I use my Bird inline wattmeter with a sampling plug (-50 dB). I put the 50 Ohm load on the output side of the wattmeter. My SA connects to the output of the sampling plug for it.
As far as measuring the PEP of an SSB signal ... I am convinced it can be done using the right procedure. I've never done it and I'm not sure how to go about doing it. 😞
I connected my SR780 (spectrum analyzer, w/ PSD setting, y-axis = Vrms/sqrt(Hz)) to a pre-amp (DHPCA-100) in low noise mode/full bandwidth with different transimpedance gain settings (10^2 - 10^6 V/A) and tried to probe across a resistor e.g. 390KOhm. How do I convert the Vrms/sqrt(Hz) to Arms/sqrt(Hz) in this case? Thank you in advance. I would greatly appreciate any reference material I could read to better understand this.
First of all, a transimpedance amplifier converts Current to Voltage. So, we do not probe *across* a resistor (my opinion). If you have a high impedance signal source that you want to connect your spectrum analyzer to, then here is how I would proceed.... You connect one end of a very high value resistor to the signal source. You have your 390 KOhm. The other end connects to the input of the transimpedance amplifier. The point of the transimpedance amplifier (TIA) is that it has a very low impedance input (as I understand it). So, the current going into the TIA is I(in) = V(source)/390K. If the amplifier gain is set to Av=1000, then the output voltage would be 1000 times this or V(out) = [1000*V(source)]/390K. I actually have not dealt with V/sqrt(Hz) & A/sqrt(Hz) before, but I am assuming we just use Ohm's law to convert between the two.
You could ask W2AEW. He is one of my goto guys when I get stumped ... here is his TH-cam Channel link
th-cam.com/users/w2aew
Also ...
en.wikipedia.org/wiki/Transimpedance_amplifier
and
circuitdigest.com/tutorial/transimpedance-amplifier-design-working-and-applications
What type of coax do you recommend for the test leads?
Well...this depends on the application and the frequency. We are remembering that coax has loss which varies with the specific coax you choose and the frequency you are working with. This loss, then, could affect the accuracy of the measurement depending on how critical this accuracy might be to what you are doing.
When amplitude accuracy is a premium, I use as short of a piece of low loss, 50 Ohm coax as possible. The larger the diameter coax, the lower the loss ... with the trade off of flexibility.
For many of my measurements I just use some nice, very flexible RG-58 patch cables because I am more interested in frequency content or relative amplitude (one pip's amplitude relative to another) than I am in high accuracy, absolute amplitude measurements.
If absolute amplitude isn't an issue, you could use any good quality, 50 Ohm coax....with the emphasis on *good quality*. Go to www.pasternack.com/ for high quality cable and connectors. They even will make professionally built, custom cable for you. Not cheap, but quality all the way. 🙂
I've bought from them before. I'm new to the spectrum analyzer game. Primarily working on duplexer tuning for pur repeaters. I'm using rg400. Wasnt sure about rg58. Thank you.
@@n5ad If you are using a spectrum analyzer for duplexer tuning, it'll need to have a tracking generator output and you will need a transmission/reflection test set (needed for the Return Loss adjustment).
When doing Duplexer tuning, you should use double shielded coax like the LMR400 or RG400 and make sure the SA has enough dynamic range to handle the job.
Here are some links that you might find helpful ...
See
th-cam.com/video/ZZHknVp3asc/w-d-xo.html
for the basics
and
th-cam.com/video/bhh2T7O-omM/w-d-xo.html
for the tuning process including using an SA for the job.
If you are doing a hybrid-ring duplexer, they are a bit of a different animal. I cover this in
th-cam.com/video/SSsnw6VygkI/w-d-xo.html
Hope all of this helps! 🙂
Oh, I've been watching your videos. Very informative. I have the rigol 815tg. Good to go there. Just don't have the reflection test set. I'm managing without it. I check both sides through my bird wattmeter after tuning.
@@n5ad Aaaaah! You can use a nanoVNA for tuning the Return Loss portion. It'll do a much better job for you on that than the Bird. It just cannot do an adequate job for the reject portion of the adjustment ... the whole dynamic range thing.🙂
I'd love to see if you would be willing to tune a duplexer for me. I can't find anyone to help me
I *do* tune duplexers. I am in the midwest right on the Mississippi and prefer folks to bring them to me rather than doing the whole $$$hipping thing.
Well ... I also have videos on how to tune a duplexer. Following the instructions in these and using a nanoVNA you could get a pretty good tune (not 100% ideal because of the limitations of the nanoVNA).
The first video covers the BASICS behind the whole thing: th-cam.com/video/ZZHknVp3asc/w-d-xo.html
The second video covers that actual tuning process: th-cam.com/video/bhh2T7O-omM/w-d-xo.html
If it is a Hybrid-Ring Duplexer, then you want to take in this one, too: th-cam.com/video/SSsnw6VygkI/w-d-xo.html
If you are unfamiliar with the whole VNA thing, I have a whole series on these.
Hope this helps.
@@eie_for_you I'd be willing to ship to you and pay for return shipping. Let me know how to contact you and discuss
Your location? Duplexer frequencies? Duplexer PN?
Can you review this conversation and perhaps tell me if this gear can help me in this particular regard?
Your videos are great, but Im not getting the info I need.
''wideband spectrum analyzer [0 to 25 GHz] and use simple heterodyne mixers to increase the range to 100 GHz. The added benefit would be being able to identify frequency and modulation, if any. One of the best ever made is the HP 8563E which is widely available for under $3000. you can easily reach up into Millimeter waves ranging for 30 to 300 GHz.''
''Spectrum analyzer, I only know how it is being abused (by environmental people from gov). No idea yet how I can use it. I only know broadspan is being used, and that in narrow spans the important info is. But no hands on experience, or what valuable info I can get out of it.
Long story short. Over here when getting hit with frequencies, I only hear it (my brain is hit with a frequency and sent down to my auditory...aka tinitus (which doesn't exist in my opinion, aside from radio waves bombarding the brain)). Should theoretically be AM/FM. But I only know that it is used to influence the weather over here. Geoengineering.
What I understand, you need to input what you are looking for in a spectrum analyzer. And I have no idea what frequency I am looking for.
That is my current understanding from spectrum analyzers. No idea yet If I can use it yet.
But I like this idea the way you present it. But I doubt the gov will tell me what frequencies they are using on their top secret military experimentation.''
I can truthfull not provide any input on this subject. If you do not know what you are looking for, then you cannot set up a spectrum analyzer to look for it. If you set it to very wide span, then the signal you might be looking for could be totally washed out and invisible because of the chosen RBW. If yo set the RBW very, very narrow to avoid this, then the trace time would be very very long and you might miss the signal then as it could be coming and going; it could be present when your instrument isn't "looking" and not when it is.
Looks like you deleted my comments, I understand.
I'm glad that you understand. The object of this channel is the discussion of electronics, not my choice of computer wallpaper.