#359 How to properly use a NanoVNA V2 Vector Network Analyzer & Smith Chart (Tutorial)

is this antenna good or bad and for which frequency is it useful a question I'm often asked because a lousy antenna reduces the range of a device considerably or another question did the supplier cheat on this filter at the end of this video you will be able to answer these questions with confidence and you know everything you always wanted to know about the Smith chart for about fifty dollars is this a good deal great to YouTubers here is the guy with the Swiss accent with a new episode and fresh ideas around sensors and microcontrollers remember if you subscribe you will always sit in the first row if you use antennas or filters your most important tool is a vector Network analyzer or VNA it is essentially like a multimeter or an oscilloscope but until recently nearly nobody had one of those because its price tag started at around ten thousand dollars with the appearance of these Nano vnas the price dropped to way below 50 the first generation had a limited frequency range with the new version 2 Generations range of 3 gigahertz such a device is a must for every Advanced maker time to learn how to use it and how to avoid the most common mistakes in this tutorial we will cover what is the difference between a VNA a spectrum analyzer and a vswr meter which questions can be answered with a VNA how does the VNA display its results and how to read them why is it important to know the limitations of the cheap dnas and how can we overcome them why and where do we need to calibrate our instruments and what happens if we do not do it how is the quality of those devices do they provide correct information which additional software packages are available first question what is a VNA it generates a signal and measures the amplitude and the face of the signal coming from the device under test or dut simple other than the ohm meter which only can measure resistance it also can measure capacitance and inductance because it also measures the phase between voltage and current this is the main difference between a VNA and a spectrum analyzer with a tracking generator Spectrum analyzers only measure amplitudes but the Spectrum analyzer can characterize external signals from transmitters what problems can be solved with the VNA let's assume a simple system consisting of a transmitter a cable and an antenna that emits the power into the air of course we want that all power is emitted this happens if the transmitter's output impedance is well adapted to the cable's input impedance and the cable's output impedance to the antenna matched means they have the same impedance generally this impedance is standardized to 50 or 75 ohms for this video I will concentrate on 50 ohms systems if these impedances do not match signals are reflected do not reach the air and heat the transmitter in the old days we had vswr or short SWR meters for that purpose they measured the forward and the reflected power as we see here if there is no reflected power the SWR is one if we want to know more we use a DNA to measure the different parts impedances and decide if the match is good or bad and what we have to do to change it cool unfortunately a few areas can happen during this process and we need a little Theory to avoid them how does a VNA work it has one or two connectors called ports or in the case of the Nano vnas channels let's first focus on Port 1. this part emits a signal and at the same time measures the amplitude and the phase shift short face for the reflected signal if you know the amplitude and the face of a signal you can calculate the impedance of the device under test and show it on a screen it is essential to know that these are the only measurements a VNA does on Port 1. the rest is just displaying these results for example this VNA shows the impedance as well as the amplitude for a particular frequency nice but most of the time we want to know the course of these values across a frequency range this is why vnas draw amplitude and phase curves across frequency ranges on the Nano vnas the amplitude is called logarithmic magnitude or log Mac and the face is called phase the amplitude curve is more famous because it is used to determine the quality of a match as we saw before with the SWR meter the higher the amplitude of the reflected power compared to the forward power the worse the match log Mac and SWR show the very same thing just for a different Community as we will later see the main differences between an SWR meter and a VNA are the VNA can measure and display also the face of the signal because the VNA has a built-in transmitter it can sweep frequencies and show curves the SWR meter often is built for much higher forward powered so a one part VNA like this n1201a is sufficient to characterize antennas why does this Nano VNA have two ports the second part is a receiving only port for filters we are not only interested in the reflected power on Port 1. we are more interested in the curve between the input and the output of the filter and this is why we need this receiving Port the rest is the same we can display amplitude and face on Port 2 the same way as on Port 1. but here we see the measurements of the signal coming of the filter not the reflected signal by the way the reflected signal is called S11 because the VNA transmits and receives the signal on Port 1. the signal measured by Port 2 is called S21 because it is transmitted by Port 1 and measured by port 2. there are also s22 and S12 which can be measured by exchanging Port 1 and Port 2 on the Nano VNA so far we only dealt with simple curves across a frequency range how does the VNA display impedances it uses the Smith chart this is a Smith chart scary but it is Handy and vital each point of the diagram represents a impedance we go through the three most important points first a pure 50 ohm resistance shows up right in the middle this is the Holy Grail where we want to be all Shooters know precisely what I'm talking about the next point is here nothing connected to Port 1 or open and a short circuit or short shows up here you will use these three points over and over if you work with vnas all points on this line from the short via the 50 ohm to the open are purely resistive I show you that in an example I have a 500 ohm potentiometer connected to a nano VNA you see what happens if I change its resistance from 500 to 0 ohms the point moves along the center line only in the end it turns away from the line why because the potentiometer also behaves like a coil and therefore has an inductance which is added to the resistance I did not know it but the VNA detected it as a small phase shift between voltage and current a sign that an inductance is in the play why do I know that this is an inductance because I know that above the center line we find all inductances below the line by the way we find all the capacity intenses you do not believe it here I connect this beautiful variable capacitor I bought for my tube radio from video number 355. it starts nearly as an open which is quite clear if we look at it the plates are not connected and are far from each other if I turn the capacitor this capacitance gets bigger and we see the point moving along the Outer Circle below the center line unfortunately I do not have a moving coil but the same would happen with it just on the opposite side again the measured values are the same as before amplitude and phase the VNA only shows more information if we add a capacitor in parallel to the potentiometer we can pull the point back to the center line you see we can use a capacitor to neutralize the inductance of the potentiometer I do not need to care about the values the VNA shows me and when I have to stop cool but unfortunately I cheated on you I only used a frequency of around 10 megahertz if I change the range from 1 to 20 megahertz Things become different suppose I leave the two parts where they were before I get now a curve why is that capacitance and inductance change with frequency even if the part does not change and this is what the VNA shows us without any effort for example we see that the curve crosses the middle line a second time at one megahertz in addition to the 10 megahertz we saw before and it nearly hits the short position at 20 megahertz so our potentiometer and capacitor behaves like a piece of copper at 20 megahertz strange but true now we can try to answer the question would this be a good match if it were an antenna ask the shooters how much point they would get if they hit at those positions the Smith chart is precisely the same the distance to The Sweet Spot shows us the quality of the match here we would have the best match at 10 megahertz with the closest distance to the 50 ohms sweet spot as seen before we can also check the quality of the match by looking at the SWR curve it shows the distance to The Sweet Spot and really it is very flat up to about 15 megahertz then it decreases rapidly because the distance gets bigger and bigger at The Sweet Spot the SWR would be one now it is around 3 a bad match you see we do not need a Smith chart to just know if an antenna is good or bad the SWR is sufficient for that purpose when do we use the Smith chart when we want to know how we can compensate for a bad match for example and for calibration as we will later see by the way if you talk vswr to an RF engineer he immediately knows you are an amateur radio operator he would never use this word he uses return loss in DB which is the same just different and of course it sounds more professional you can also display the return loss on a nano VNA it is the lock Mac from before and it is around -6 DB at an SWR of 3. now we have the basics to start working with the VNA the most important thing you have to know is calibration never use an uncalibrated DNA never it will show wrong values and fool you there are two reasons for calibration one the VNA itself has lots of non-linearities and two the measurements heavily depend on where you attach the dut y you probably ask yourself why is it possible to drop prices from ten thousand dollars to fifty dollars is the quality of these devices okay or do they display crap and here comes the calibration into play even if those cheap instruments are not accurate at all you still can get good results how is this possible if we use well-known duts and tell the instrument their exact value it can't remember this fact for example if I attach an exact 50 ohms resistor to Port 1 and tell the instrument that it is 50 ohms it will later recognize a well-matched antenna and also display 50 ohms so far so good but do we need to have a ton of resistors capacitors and inductances to calibrate the instrument on all points of the Smith chart fortunately not we only need three and open a short and a 50 ohm load if we calibrate even a cheap instrument at least three points it will display all other points with acceptable precision but do not forget if we omit this calibration these cheap instruments can show very wrong measurements also the professional ones by the way the calibration process is relatively easy first choose the frequency range you want for your calibration this is very important because the Nano VNA invalidates a calibration as soon as you change the range then we go to the calibration menu and start with connecting the short to the VNA after waiting for a short time we can go on with the open and the load this is called Sol calibration if we connect both ports and tip through we get a salt calibration now we can save it in one of the seven memories here the instrument shows us if it is calibrated without this Capital C it is uncalibrated you probably remember I said you would see these three points over and over now you know why we have to calibrate the instrument every time we change the frequency range you might say why not do a wideband calibration at the beginning then the instrument should know its calibrations at each frequency theoretically this is true and the n1201 sa does it like that but those small devices only measure 101 or 201 points per scan if you start at one megahertz and end at 3 gigahertz you get a calibration Point each 30 megahertz which is more or less useless most antennas for example have a much smaller usable range than 30 megahertz by the way if we switch the calibration off we get very different and wrong results we increased the Precision of our device by factors using this simple calibration method this is why you also have to order your VNA with a calibration set according to court Polson a calibration specialist the SMA calibration sets coming with the Nano VNA V2 are quite good up to 3 gigahertz which is very astonishing a professional calibration set can easily set you back two thousand five hundred dollars and more this was the first reason for calibration the second is the calibration plane if we calibrate our instrument with a standard set we establish a calibration plane right at the SMA connector maybe you ask yourself why we have a special open calibrator because there is a difference of a few millimeters between nothing and open especially for higher frequencies as soon as you add a cable or an adapter to your VNA the calibration is no more accurate here is a simple example this antenna only has a female connector which does not match the female connector of the Nano VNA I can solve this problem by adding this simple adapter look what happens if I add the adapter the open point is shifted considerably because the signal travels to the newly established plane and back our instrument is no more calibrated I have to calibrate my instrument at the newly established plane but if I have no female calibration set fortunately the Nano VNA can correct this error by using a port extension called electrical delay on the Nano vnas if I enter 165 Pico seconds the open is back where it should be good enough for us makers if you do not trust me you can visit Allen's W2 aew Channel he covers that and many other Specialties of the Nano vnas the same but much worth applies if you want to measure on this demo kit because you need a pigtail to connect the VNA to these tiny UFL connectors now we have two possibilities because the board has an open a short and a load you can calibrate on this board or use the port extension as before of course with a much longer delay of 1.95 nanoseconds both establish a calibration plane at the end of this pigtail here are the results with calibration on the board as well as with the port extension the measurements are very similar the result with the calibration plane at the SMA connector of the VNA is very different and wrong with all this knowledge we can answer our question from the beginning which antenna is better they look very similar same manufacturer and same type they should work on 144 to 148 and on 430 to 440 megahertz as shown before I established the calibration plane on the adapter for frequencies between 100 and 500 megahertz for an overview this is okay I use 201 measuring points and get a space between the two measurements of two megahertz enough to check if the antenna is terrible but not enough to see if the antenna is good both antennas have two dips unfortunately the dips of the fake one are not deep enough so it is not usable for our purpose if we look at the Smith chart we see that its curve always is in the capacitive area maybe adding some inductivity would get a better response the real one is far from an optimal antenna but it steps at least are in the right place we could now calibrate our VNA around 144 or around 430 megahertz to get better measurements for the two ranges but I think you got the point as said in the beginning we can also measure filters if we have a two Port VNA we connect Port 1 to the input of the filter and its output to Port 2 and measure S21 we have some filters on the demo kit to check the effect but before we can do so we have to calibrate the through this is either done with such an adapter or in the case of the demo kit with this through after establishing a salt with a calibration plane at the kit and for the frequency range of 5 to 15 megahertz we see the expected dip at 6.5 megahertz as well as the Peak at 10.7 megahertz for the other filter because the noise floor of this Nano DNA is around -75 DB we cannot measure very good filters here we need a professional device with a noise floor below 100 DB in my lap the highest frequency I use is 2.45 gigahertz for Wi-Fi and this will stay for the next years I do not think that our gadgets will move to 5.8 gigahertz Wi-Fi soon so now it is the time to invest in this new technology if not already done a few words about the available software I use the vnaqt software for this video you need it also for firmware upgrades it is simple and thus more or less the same thing as the firmware on the device the Nano VNA saver software is much more elaborated but also has a steeper learning curve you find the links in the description summarized vnas create a signal and measure impedances of duts like antennas or filters they measure amplitude and phase to determine impedances they display amplitudes phases and impedances over a frequency range either in X Y charts or in a Smith chart the Smith chart is made for systems analysis SWR or return loss curves help for quick checks to get the needed accuracy vnas have to be calibrated use a sole calibration for one port antenna characterization and soul T calibration for two Port filter measurements for the Nano vnas the calibration range always is the same as the measuring range always establish the calibration plane where the measurement is planned either by connecting the calibration set at this plane or by using Port extension the Nano vnav2 is an ideal device because it covers all hand bands the 433 and 868 915 megahertz ISM bands and the 2.4 gigahertz Wi-Fi all we need for 50 dollars it has two parts and therefore can characterize antennas and filters it is critical to know that it only measures a maximum of 201 points in the range only with the PC software you can extend this number so it is necessary to adapt the frequency range to the questions you want to answer for a quick antenna check the full range up to 2.5 gigahertz is good enough if you want to characterize a filter you have to use smaller frequency ranges the most important limitation is the small number of measuring and calibration points with the effect that we have to calibrate the instrument way too often its limited dynamic range does not show the quality of powerful filters as always you find the relevant links in the description I hope this video was useful or at least interesting for you if true please consider supporting the channel to secure its future existence thank you bye

Channel: Andreas Spiess

Views: 257,324

Keywords: esp8266, esp8266 datasheet, esp8266 project, esp8266 tutorial, greatscott, guide, hack, hobby, how to, iot, lora, lorawan, npn, p-channel, pnp, project, tutorial, wifi, Raspberry Pi, Zoom, Microsoft, Teams, Home Assistant, Docker, VNA, nanoVNA, nanoVNA V2, SAA-2, SAA-2N, AliExpress, Aliexpress quality, arduino, arduino project, beginners, BJT, diy, do-it-yourself, eevblog, electronics, esp32, esp32 datasheet, esp32 project, esp32 tutorial, vector network analyzer, VNA tutorial, nanoVNA tutorial, nanovna V2

Id: _pjcEKQY_Tk

Length: 25min 16sec (1516 seconds)

Published: Sun Nov 01 2020