Selecting a Spectrum Analyser - Page 1
Forum section: electronics / testgear

author: PixieDust
author_rank: Frequent Contributor
timestamp: October 09, 2019, 04:08:19 am
content: Hi, how does one determine the frequencies that the spectrum analyser should be able to cover for your project? This is for Pre-EMC compliance purposes.

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: October 09, 2019, 05:31:41 am
content: The answer is for EMC precompliance is sort of an "it depends" situation, but here's a couple app notes/white papers that might help:EMI precompliance fundamentals app note (more basic):http://literature.cdn.keysight.com/litweb/pdf/5992-3188EN.pdfMaking conducted and radiated emissions measurements app note (more advanced):http://literature.cdn.keysight.com/litweb/pdf/5990-6152EN.pdfIf you're trying to lock down a specific model or ID key needs, I'd highly encourage you to call our support folks using the link in my forum signature - they are super helpful for stuff like this.

author: Berni
author_rank: Super Contributor
timestamp: October 09, 2019, 06:37:54 am
content: It all depends on the EMI standard you are trying to comply with. There are MANY different ones out there.But in general you will want to be able to go up to 3GHz

author: tautech
author_rank: Super Contributor
timestamp: October 09, 2019, 06:42:15 am
content: Quote from: PixieDust on October 09, 2019, 04:08:19 amI've sold numerous 2.1 GHz SSA3021X just for this. Even 1.5 GHz SA's can do the job admirably and all you need to go with them is a set of sniffer probes.There are bigger things to consider like if you want to get properly into RF where rather than just a SA a SA/VNA combo might be a better choice in the longer term.Anyways, suitable instruments start at ~$1400

author: PixieDust
author_rank: Frequent Contributor
timestamp: October 10, 2019, 01:08:49 am
content: Thanks guys, will review standards and attached documents!

author: PixieDust
author_rank: Frequent Contributor
timestamp: April 27, 2020, 05:15:48 am
content: Hi guys, I have studied spectrum analysers a bit more and now I'm less sure that I even need one. I'm not designing or playing with RF signals and don't plan on it. Mostly worried about EMC compliance testing. But even here, I know that CE/FCC/etc markings don't tell which standards the device complies with, but assuming they comply with the standard that your device will be tested against - if I build up a product composed of these CE/FCC/etc marked components, I find it hard to believe that the devices will fail emissions if no RF circuits are used. I'm less confident about conducted emissions especially since I might be designing my own power supplies. But either way, what are your views on how important a spectrum analyzer is in the case of no RF work? They are expensive additions to the family for quite limited use in my eyes.

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2020, 05:32:18 am
content: As mentioned earlier, modern SA's specialise in this sort of stuff.Typical EMI test with limit line that you need to stay comfortably below before your DUT is sent away for compliance.

author: elektropionir
author_rank: Contributor
timestamp: April 27, 2020, 05:48:08 am
content: Quote from: PixieDust on April 27, 2020, 05:15:48 amBetter believe it. If you will be designing power supplies (SMPS?) that will be sold, consider that EMC will be about 50% of total work on any given project, and might cause multiple PCB redesigns and delays. You do not have to test for emissions, conducted and radiated, but for immunity as well.Power supplies are extremely complex to analyze from standpoint of RF. You have multiple capacitive and inductive couplings to every point, you have both high dV/dt and dI/dt loops, X and Y capacitors everywhere, and few meters of input and output cables to serve as great transmitting antennas.Even if you use a PSU that has CE/FCC markings that should not give you great confidence that the unit will pass the tests. You can find many cheap units from China that have all kinds of markings, and if you ask nicely they will gladly add some more. You should really test what you plan to use for yourself. Spectrum analyzers are indispensable in my opinion.Having said that for EMC any SA that can act as test receiver with above 1-1.5GHz will do.

author: PixieDust
author_rank: Frequent Contributor
timestamp: April 27, 2020, 12:42:27 pm
content: I'm currently working on a linear power supply. Not sure whether the future holds SMPS in store or just off the shelf varieties, but you raise a good point.

author: charliedelta
author_rank: Regular Contributor
timestamp: May 02, 2020, 05:07:03 am
content: As minimum it should have the EMC option such as EMC detectors but mainly Quasi peak. The EMC CISPR bandwidths depending on what standards you are testing for.Spectrum analyzers especially the ones that most of us can afford are very slow because of the Quasi peak dwell times. Its frustraing sitting there waiting for scan to complete from 1 to 30 mhz etc when you are trying to peak a circuit or switch in a ferrite bead.For this reason I much prefer a EMC receiver or even a direct sampling receiver that samples the spectrum. I prefer to use my Rohde EB200 and Perseus SDR radio as a pre-compliance tool. Used in conjunction with the RF current probes and the LISN I can work quickly making design changes. Unfortunately there are not many affordable EMC receivers on the market and I dont like the R&S ones that are nothing more than PC with a RF front end and a front panel. I would like to buy Gauss receiver but really cant afford it.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: May 03, 2020, 03:42:31 am
content: I'm no EMC specialist, but I thought that quasi-peak was strictly less than max-hold, so long as you were at the right RBW. Is that not the case? Or is there a modern situation where designing to quasi-peak is much easier than designing to the corresponding slightly stricter max-hold standard?

author: charliedelta
author_rank: Regular Contributor
timestamp: May 10, 2020, 01:56:43 am
content: You are correct it is less and designing for max hold and allowing for bandwidth plus 6db for errors would be a good safe bet. Where quasi peak is useful is when you are calibrated antennas for radiated emissions. Sure you can sit there with a calculator and calulate the values but you can easily make mistakes when you are tired or forget.I find that a EMC receiver more useful and faster when doing pre-compliance work. I also find that designing to the more stricter standard is a good way to hone your skills. I design for example to the FCC Class B requirements or whatever is the stricter standard for radiated and conducted emissions. This is really just engineering practice, there is a rarely a design that cant be tamed to be best EMC standards. Poor EMC compatibility is just an excuse for poor engineering skills rather than budget constraints. Yes the equipment is expensive only because of lack of competition in the market. The excellent Direct Sampling SDR radios like the Perseus make excellent diagnostic EMC receivers for conducated as well as radiated emissions. Its amazing how fast you can fix problems when using a SDR receiver as an EMC receiver. I really dont know how good the SignalHound is but for most of my work radiated and conducted is below 500MHZ, within range of readily available equipment. I am mostly working within the EN55011.55022,55015 and 55032 standards. And despite my primitive equipment not 1 of my designs has needed to go for further testing. I can go straight from pre-compliance to manufacturer and pass because I just set the pre-compliance standard at the highest or best standard. Its cheaper than buying a Compliance EMC receiver for 100 plus grand plus another 50 grand for transducers, antennas etc etc.

author: Chris Roubis
author_rank: Contributor
timestamp: May 10, 2020, 04:48:45 am
content: Is there any cheap versions of a spectrum analyzer that also measures wattage output, for playing around with ham radios etc. ?

author: 77algernon
author_rank: Newbie
timestamp: May 10, 2020, 11:15:52 am
content: Quote from: lordzeus on May 10, 2020, 04:48:45 amHello there!If you just want to measure the power output, a swr+power meter would be cheaper than a SA.On a SA, you would change the vertical to display dBm and make sure you measure on a 50ohm load that can take the output power (and some attenuator if you're on the heavy stuff)