 Hi, I'm Kurt for the Ham Radio Village at DEFCON29 in 2021, and I'm going to be talking to you today about some of the equipment that we use for RF testing and experimentation, more specifically for ham radio testing and experimentation. But I'm going to go over some of the more useful tools and some of the smaller support tools that we use for a lot of this experimentation. So we're going to go over oscilloscopes, vector network analyzers, spectrum analyzers, and then additionally we're going to talk about some of the other pieces that we use in conjunction with those, so signal generators and temperature controlled oscillators, dummy loads, attenuators, and then we're going to do some experimentation or I'm going to do some demonstrations with both commercial and homebrew projects, and then I'm going to show you how to test an antenna at the end, because I think that's probably one of the more common pieces that we're going to need. But let's start first with the oscilloscopes. So I'm going to reset up and we'll get started on oscilloscopes. Okay, so we're zoomed in on my table now and what we're going to talk about first are oscilloscopes. So one of the nice things right now is that the cost of the technology has come down quite a bit. This is true for oscilloscopes, but it's also true for all the rest of the equipment here. A lot of the prices are much more reasonable now for hobbyists to get into, so it might be the right time to expand your testing and experimentation capabilities at home. And first we're going to look at oscilloscopes, like I said. So for many years I used one of these, which is a mini pocket oscilloscope. These are a few hundred dollars. They are a bit limited in their capabilities, both in terms of speed and the level of voltages that they can measure. But they do work pretty decently for homebrew projects. And I will show on here with my setup right here a little bit of the difference between this and a larger oscilloscope. And nowadays the larger oscilloscope is actually not that much more expensive. So it might make sense if you have the space and a little bit of extra cash to get a larger oscilloscope. But what an oscilloscope does is it measures voltage and time. So in our vertical axis here on the screen we have voltage and the horizontal axis we have time. So we can see a delta in voltage. And from that the oscilloscopes can actually do a lot of secondary derivative calculations. So this one also shows frequency and the period of the waves if it's in AC mode. And if it's in DC mode you can also do very basic circuit logic analysis and things like that. Depending on the capabilities of your oscilloscope. Obviously the more expensive ones can do more interesting things. So what I'm using right now is I have a, this is actually a temperature controlled oscillator. Let me take this off for a second and we'll get a zoomed in view here. So this is just hooked up to a 9 volt battery right now. And this gets warm, this gets to be about 100 degrees Fahrenheit. And inside of there is a crystal. It's being fed by this little voltage regulator that I put in here. And then we have two different outputs on this one. This is a harvested temperature controlled oscillator from, I believe it was from medical equipment. And a homebrew board that someone made that has two different outputs. One is an unbuffered output, which is straight from the oscillator. And that's the main one right here. And then the secondary one is it feeds that into a chip, a logic chip, a 5 volt logic chip. And turns it on and off. So you get what they call a buffered square wave output. And that I have going to the second output right here. And this is just a 3D printed case that I made to keep it nice. And I've taken the lid off so we can see inside of it. So what it does, what almost every reference oscillator does is they run at 10 megahertz. This is a standard for almost all radio and medical test equipment is their internal oscillators are set at 10 megahertz. So you can actually use this as an input to a device. So this oscilloscope doesn't have an input. It does have an external trigger, but it doesn't have an external reference oscillator. A lot of the more expensive equipment will have a port on the back where you can provide your own reference oscillator from something like this. So what we're looking at right now is I have the unbuffered output straight from the oscillator going into a 50 ohm load. And so the almost all radio and test equipment is going to expect 50 ohms on the wire. And I'm going to actually show you what happens when it doesn't get that. But so right now we're seeing a very small voltage peak to peak is 150 millivolts or 140 millivolts. And we can see the derivative calculation of the frequency is pretty steady at 10 megahertz on here. Hopefully that's coming through on the video, but I can get a zoomed in video of this in a minute. And then we have the probe on channel one, which I have yellow and yellow on here is showing before and after the load. So this is the differentiation of the signal that would actually be going through the wire. This is the difference in voltage between what would be the shield of the cable and the center of the cable for if you're thinking about antennas and feed lines. So this is unbuffered. Let me switch this over real quick so we can see the difference on the buffered actually real quick. You can actually see the wave is not perfect. If it was a perfect, ideally what we would want is a perfect square wave. But there's actually quite a bit of ripple in this. It's not terrible, but still mostly square. You can see the trigger on the, if I adjust the trigger, you can kind of see it start to go crazy a little bit at certain points. So ideally you would want a very smooth square wave if you're going to use this as a trigger. And I think this is actually a byproduct of the way the homebrew board is set up to take the crystal output. I think we're not getting quite a 50 on load output on it. And I think that's partly what's making this look a bit wobbly. There might be some extra capacitance or inductance on there, which we're going to talk about a little bit later as well. So let me switch it over to running off of the 5 volt logic chip. So this 5 volt logic chip is taking the output of the signal of the oscillator and feeding it into the logic chip. And it's just flipping the logic chip on and off at 10 megahertz. So right here you can actually see we're way too zoomed in now. We're getting way more voltage. So let me zoom this out in here. So this is the same time frequency, but now our voltage frequency we're seeing a peak to peak of 3.92 volts. So much higher voltage we went from 140 millivolts to 3.9 actual volts. This is still AC, so this is above and below the zero point. We can actually see the wave is a lot cleaner here. You can also see the rise and fall time of the chip right here. So there's actually a bit of a slope. It's not perfectly vertical up and down. But you can see the wave is much cleaner and our voltage is much higher. So this could be a useful input for devices that can take that voltage and need a much cleaner wave. Ideally we could tweak this board a little bit and try and get the wave a bit cleaner from the other output. So one of the things I mentioned was the 50 ohms. So all of our test equipment and every radio equipment, most sensitive equipment, expects 50 ohms. That's kind of a weird thing. Why is there any load at all on the transmission cable? Well, a long time ago, I think it was Bell Labs figured out that 75 ohms is best for receiving signals. That gives you the cleanest input signal. And 25 ohms is best for transmitting a signal. So if you have a device that both transmits and receives, 50 ohms is the best compromise. So some TV antennas and things like that will be 75 ohms. Which means you have to be kind of careful when you're selecting coax you want to use for an experiment. You don't want to use TV coax because it might be the wrong resistance. But most laboratory and radio, especially hand radio equipment is going to be 75 ohms. Or sorry, I'm sorry, 50 ohms. So now what happens when we take our oscillator input and I'm going to pipe it directly in. So this probe and this input here are very high impedance, very high resistance. Which means you can put 600 volts on this thing and it will not jump, it will not catch on fire, you will not break anything. And it basically is like a black hole inside of this box. But if I pipe it directly out, if I pipe the oscillator signal directly into here, it's not 50 ohms. It's nowhere near 50 ohms. So what happens? And I'm going to zoom back in a little bit. Okay, so this is directly in and you can actually see the wave is terrible. So what is going on here? This is actually representative of the signal bouncing back and forth along the transmission cable. This is something very important in RF and specifically with hand radio, we talk about it all the time. This is actually a visual demonstration of standing wave ratio. So this means that the signal flowing across the line is actually bouncing back and forth and you're actually getting reflections of that line. And this can actually damage your source equipment that is transmitting. So if you have a radio that's transmitting into high SWR transmission system, you can actually get reflection back and melt your radio or something to that effect or damage some of the sensitive electronics of it. And so this is off of the raw oscillator. Let's look real quick at the 5 volt oscillator or 5 volt buffered. So you can actually see it does get some standing wave, but it seems a lot less affected by it than the raw oscillator. So that's an interesting property of running things through a buffer chip. They're actually using a digital chip as a buffer for these signals. It actually adds quite a bit of resilience to the sensitive electronics inside the radio system. And it's a common tactic that a lot of RF designers will use to beef up their systems. Okay, so now I want to introduce you to one of the homebrew projects that we're going to be using and actually have multiple versions of this. This was a project originally published by Jeff Anderson, who is K6JCA. And you can find this diagram on his website. And this is a very simple direct conversion Morse code or CW transceiver. So it sends and receives. It is very basic. It doesn't have a lot of filters, which is one of the properties that we're actually going to demonstrate with it. And what I have is I actually have two versions of this that I built. So his original version, he managed to fit in a nine volt battery. So I have a similar attempt where I've got this on two boards and all the equipment started on there. And then I have my original prototype board or promo proto board with all of the pieces in through hole design. So I can get them in and out and some sockets so I can change some pieces out when I was testing things. And again, I'm using a dummy load and I didn't really show this up close before, but this is a SMA connector with two 100 ohm resistors split off the side. And this gives us a pretty good 50 ohm load for very small signals. So let's go through and do a quick demo of what this does. So and how we see it in the oscilloscope. So actually real quick, this is using a crystal oscillator. So this is at 7.045 megahertz, which is inside the ham radio bands in the 40 meter band, which means we can we can test on here as long as we're not causing harmful interference. And we're going into a dummy load so this won't leave the garage. I'm not really concerned about it. So we're going to hook up to the output here and I've got a bunch of breakout pins to make measuring this way easier for myself. I did a lot of testing on this board. Okay, so this is actually my send button right here. So if you're thinking about Morse code, this would be what I would use the straight key to send Ditz and Dawes. It's not really very optimal, but it works. So when I send on here, what we'll see or what we see is a peak to peak voltage about 360, 370 millivolts. And we see it's trying to measure the frequency. It's getting it's jumping around between 6.99 something to 7.067 and it does say 7042 a few times. So you can start to see a little bit of the breakdown of the derivative measurements on the oscilloscope. But what we do see here, we got a big jump in voltage there. Our voltage is jumping like crazy. Okay, so now we're actually seeing 5 volts and then it jumps down. Okay, there we go. So we're getting more stable. And actually now that the crystal is warmed up, what we're actually seeing, or the transistor is one of the two, warmed up, we're actually seeing between 4 and 5 volts. It's not very steady. Again, homebrew project, these things are very sensitive to environment and touching. So it's actually stabilized a bit at the higher voltage. Lost it. Right, there we go. Okay, so you can see the wave is actually pretty clean. It's bouncing around a little bit because the device itself is not incredibly stable. But you can see that this sine wave coming out of the crystal and going through this analog circuit actually maintains its shape pretty well. We don't see a lot of the rippling or the squares that we saw. Which also means that this 50 ohm load is pretty well matched for the transceiver, for the transmitter, and we're not getting a lot of feedback or a lot of bounce in the circuit. But yeah, we can see even with everything warmed up and it's stabilizing, the frequency calculation is not exact. 7.042, and it should be 7.045, but it's pretty close. So let's look at the other version of this. I'm going to take this off of here, turn this off, put this dummy load on the little micro one. This one is not going to have the same output level as the other one. Zoom in, and I need, this doesn't have a button built in. So I have a keyer transmitter, I think it's this one. And I actually didn't bring anything out here to short this. I'm going to bring my key out here, and there it goes. Okay, so we're seeing 4 volts peak to peak. It's jumping around 3.3 to 4.2, and I forgot what frequency crystal is in here, but we're seeing a similar jump around from 6.9 to 7. something in here. But you can see the wave looks almost the same, it's fairly stable. The waveform is fairly stable despite the instability of the actual device. But this doesn't actually look terrible for such a tiny device. But one of the things that you can't see right here, because we're reaching the limitations of the oscilloscopes used in this range, is that anytime you generate a signal, there's actually harmonics. So at 2 times the frequency, and at 3 times the frequency, and at 4 times, and so on and so forth, there are harmonics being generated by this device and transmitted out, emitted from the device. On a commercial transceiver, you will have filters above and below the transmission point, most certainly stronger ones above than below. And they will be engaged depending on which band or which frequency range you're using on the device. And I can demonstrate some of those, but I'll demonstrate some of those later, but what we're looking at, or what I'm trying to show right now, is that we can't actually see those harmonics being generated by this device with this type of test setup. And I'm going to switch equipment to the spectrum analyzer, and we're going to talk about looking at the signals in a different type of domain, rather than voltage and time. We're going to look at them in a different domain. We're going to look at them in frequency and voltage. Okay, before we move completely off of oscilloscopes, I wanted to give a quick comparison of the micro oscilloscope versus the larger one, just in terms of what you can see on them. This is actually pretty full-featured. It has a signal generator up to four channels in. It has two analog channels and two digital channels, which is pretty full-featured for a device this size and this price range. But it is definitely not as sensitive as the larger oscilloscope. But we do see, you can look at, this is the 7.045 MHz chip, and you can see it actually picks it up just fine, and it does a good measurement. You can't do derivative frequency or things like that on here. You actually just have to take a snapshot and measure it and take your best guess at what it is. You put measuring pieces on there and it will actually tell you the delta. I can't do it while I'm holding it like this, but you can move the measuring lines around and it will tell you the voltage, the estimated voltage, and the delta between the lines. So definitely not a bad tool to have around, especially if you can't fit a full-size spectrum analyzer or full-size oscilloscope, or don't have the room for one, or don't have the money. So definitely a good tool to have around. Alright, so now we're going to talk about measuring the signals in a different way. We're going to measure frequency and amplitude with the spectrum analyzer. So let's see if we can see this. So this is a very wide view right now. This is all the way from zero hertz, which is DC, to we're stopping at 350 megahertz. This chunk right here where it's super big is actually the FM radio band. And there's a lot of FM radio stations because I live in a big city. So those are very strong right here. So almost all of the handbands fit way below, or at least that we're concerned with right now, fit way below on the left side of the screen. So we're going to have to change our view a little bit. And the first way I'm going to measure this is actually just with an antenna. I'm not going to connect anything. And one thing you'll notice is that actually a lot of radios actually have displays like this because a spectrum analyzer is basically the front and half of a radio. It's detecting the signals. It's doing the signal detection, but it actually doesn't do decoding or demodulation. So it's basically the front and half of a radio. And so what I'm going to do here is I'm going to change the frequency and we're going to start around... Where do I want to start? We'll start around 6.8 MHz. And we'll go to 7.1 MHz. So we get a smaller band. That might be too small, but we'll see if this works. So the way that this hardware is designed, it actually doesn't do as well scanning smaller areas in finer detail. But we should be able to see. So this should be at 7.045. So somewhere a little bit to the left of the screen here. Or to the right of the screen. Sorry. So let's see if I can turn this on. Oops. I'm going to turn my power back on. All right. So there's our signal right there. And it actually looks pretty good. It's not very strong. It's at negative 78 dBm. Remember that's millivolts. Decibels is a logarithmic scale. And we're using millivolts as a base. So this actually doesn't look terrible. But what we're not seeing when we're zoomed in this far. Let's go, let's change the top end of this to be 15 MHz. So now we have a big, quite a big range right here. Now so our signal should be way over here to the left. And you can actually see it is picking it up. This type of homebrew project, it actually admits some signal, even though we're not powering up the transistors. They actually have just like a warm state I think that lets them emit some signal. You wouldn't be able to see it unless you're really close to it. But I've got this only a few inches away so I can pick it up. So it's actually registering at 7.0 for something, which is where our frequency is. But you can also see there's another spur right here. And I think that's our harmonics on me. Transmit here. Okay so there you can actually see two spurs here. They're not super well defined. This thing isn't super powerful. Let me try and zoom out a little bit more. So let's stop this at 22 MHz. Let's see if we can see. So it's actually not bad. At least, there we go actually. If I move it a little bit closer, you can see it a little bit better. Let me see if I can range this a little bit. So these spectrum analyzers are very sensitive. So now we can actually see the second and third harmonic here of our frequency. And these are what commercial radios need to suppress. So they need to have filters to push them out. This homebrew radio doesn't have it. Again we're only emitting a few millilots here. It's not really that much of an issue. But this also sort of gives some insight into why the ham radio bands are spaced the way they are. So like 7 MHz is the 40 MHz band or 14 MHz is the 20 MHz band and then 15 MHz is 21 MHz. So those are all harmonics of each other. And that's one of the reasons. So if your ham radio equipment malfunctions you're actually only affecting other amateur radio enthusiasts rather than affecting some commercial frequencies. At least in a lot of cases. They're not all like that but the majority of them are. So this is showing, again this is showing frequency and amplitude. Bring up my notes again. So another way that we can check actually we can actually use a short wave radio. And you can hear that. That's right at 7045. And if I transmit the signal goes from, it's actually still, if I move it close you can hear that it's going to move it further away. The signal drops down. But then if I transmit you can hear it. So if I take this up to 14, let's start at 1480. And we'll see if we can find this. So there it is. So there's the harmonic somewhere around here. And sorry if that's obnoxious sounding. So that's another way to demonstrate that there is leakage on these other bands. And like I said a spectrum analyzer is really just the front end of a radio. Anyway it can be a little bit more sensitive. But it's doing the same things that the front end of a radio does. The receiving signal side of the radio. So another way to measure this. I'm measuring right now. I'm not connected to anything. I'm just measuring with an antenna. Nothing's physically touching. Which is not bad for stronger signals or when you don't need things to be exact. But there's actually a lot of interference here for just from the air. Like you saw how many signals were here if I zoom out to go in the hundreds of megahertz. So let's go to 200 megahertz top end. There's a lot of signals around me from the fluorescent lights, from Wi-Fi hotspots. Wi-Fi hotspots are much higher. But from all sorts of things there's all sorts of interference. If you need to do a cleaner analysis of a signal you can actually run the output of something directly into a spectrum analyzer. But a spectrum analyzer has a maximum voltage and power that it can absorb. So what we need to do is we actually, even with something this small we actually need to use a tool called an attenuator to reduce the signal to a point where we're not going to blow up our nice equipment. So I've got several attenuators here. So this one can attenuate 10 watts of input power and it drops it by 20 decibels, which is pretty significant. And then I've got smaller ones here. I've got 10 dBs and 20 dBs. So these are usually 2 watts. This is up to 10 watts in. So this one I can actually use with a 5 watt output radio and I can drop it down to something that's safe for this. What I'm going to do, I'm going to grab some cables real quick and set this up and I'm going to put this on the output antenna of our little test radio and I'm going to put it directly into the low input on the spectrum analyzer. So through the magic of editing, you're now seeing another take of this. But what I have as I have the proto board is going through the attenuators directly into the spectrum analyzer and I'll move this around a bit to fight the glare from the overhead lights. And I've got the oscilloscope still hooked up just so we can see when the output's happening and stuff. And what I've done is I've actually gone into the menus on here and I've turned on harmonic measuring on the spectrum analyzer. So it'll actually tag not just the peak but the second and third harmonics or however many you're showing on the screen. So right now I have it from 6 MHz to 20... it's actually up to 35 MHz. So it's pretty wide range right now. So we should be able to see at least the first and second harmonics. So I've got this powered on and if we push the button it'll actually say... let's see if we can see that there's a peak and then a second peak and a third peak. And those are the first second... or the second and third harmonics from this device and they show up right at the place where you would think they would. So it says plus 7 MHz so it's 7 to 14 and then 14 to 21. And the second harmonic is negative 30 dB down from the original signal and the third harmonic is negative 34 to 40 down from the primary signal. So this is important because the way that the FCC writes the rules your harmonics have to be a certain level below your primary signal. I believe it's negative 68 dB or 68 dB down from your primary signal. So this is not really in compliance. You couldn't sell this to anybody or anything like that but it's very interesting to test with and you can see the extra or spurious emissions from the device. So this tool is really useful for measuring those and making sure that you understand what the properties of the output are for your device. And the next thing we're going to do is I want to hook up an SDR and we're going to do similar measurements on the SDR we're not going to do it directly but we're going to set up an SDR with a laptop real quick and we'll look at that. So now what I've got is I've got my little Windows tablet hooked up through a USB extender to a very inexpensive SDR, this is RTL SDR and I have it going through an up converter that pushes up the frequency 120 MHz and that's because these SDRs are not very good at actually picking up lower frequencies the larger wavelengths they don't do as well. They can do okay but this is a nice little device to have around for messing with the ham radio bands especially since there tend to be much lower frequency than a lot of modern radios. And I have this hooked up to just a very simple random wire antenna that we're going to actually look at later with the V&A and I also have this running just so we can do a comparison but what you'll see hopefully shows up in the video at the bottom right here is there's actually a spectrum graph that looks very similar to this it's a little bit more detailed obviously there's more pixels here and then there's a zoomed in version on this lower section of the screen right here and so when I transmit so this is picking it up and so is this the contrast isn't as great on here I'd have to play with the settings to get it to zoom in but this is what I mean when I say that the spectrum analyzer is basically doing the same part as the front end of a radio which is pulling in the signals and putting it into a format that you can start demodulating or inspecting and that's really all this is doing too is it's turning the in phase and the quadrature is turning the signal into sound on the left and right channel and then the software here is doing all the work to turn this into audio the audio is coming straight from the software there's no audio real output on this even though it's sending through an audio signal it's actually not what you would think of as an audio signal traditionally so and you can actually see on here because the computer is doing most of the work we can actually get a little bit more detail and you can actually see that the signal is drifting a little bit as the device changes as the device warms up or down or if I touch something it changes it quite a bit actually that's interesting it drifted all the way out of the range that we were actually looking at so it's not you can tell it's not very great for a home group device but the SDRs and the spectrum analyzer is very similar in their functionality this is obviously limited to specific types of measurements that it's doing the SDR is limited by how quickly it can sample various frequency ranges at what resolution it can do it and then the software on the computer does all of the more difficult calculations so that's just a quick demo of using a SDR in a similar way to a spectrum analyzer I actually was not done with spectrum analyzers one important aspect that I forgot to talk about for signal finding is you can use a spectrum analyzer or any wideband device that can receive the signal frequency that you're looking for you can use a directional antenna with that device to try and locate something by using the directional aspects of your antenna and pointing it at the thing that you're looking for so what I have right here is this is a passive loop antenna off of a AM radio stereo but it is directional off of the broad side of it so if I set it here on the ground or on the table it's essentially pointing up and down and we're still picking up these really strong FM radio signals here at 103 megahertz is the peak one but if I pick it up and I turn it I know the towers that way I'm inside a garage with metal doors and stuff but we can see that the signal gets higher that way and if we're looking at lower frequencies like amateur radio bands or something we can do something similar so if I go to frequency start we'll go to let's go to 14 megahertz and we'll stop it at 14.2 megahertz ok so now this has got to come down it's got to figure out where it is so you can actually see our noise floor and decibels right here it's about a negative 110 which is pretty good so usually I can find a signal here somewhere but I am inside of a building so usually at 14.074 is a very common protocol called FT-8 but it doesn't look like I can pick it anybody up transmitting inside of my garage I might be able to get it with the other radio so let's try something else here so like I said you can use lots of different ways you can do this with a spectrum analyzer and you get a nice visual we can turn on the the waterfall which might help us be able to locate something you'll see at least a lingering visual representation on here but let's try using a broadbanded radio so I'm going to take this directional antenna off of here I'm going to stick it on my little tech sun shortwave radio and this one is nice because it has an external antenna port on it I'm going to do the same thing we're already there so we're going to go to 14.074 turn this on and if I can find it I'm not seeing it I think it's just because I'm in the garage I can usually pick it up if I'm outside so maybe I'll do another quick shot of messing with this outside but yeah this is a broadbanded receiver this is a commercial one a tech sun shortwave receiver a spectrum analyzer and an amateur radio what you really need here is some sort of directional antenna that you know most of the properties of so you can use it to hone in on your signal it's also nice to have a visual representation this has a signal strength bar this one obviously has the decibels most amateur radios will have a signal strength bar and s meter but it also helps to have some sort of visual feedback and or audio feedback to know how strong the signal is as well and that will help you find the location or direction of the thing that you're looking for alright last but not least in terms of equipment we're going to be talking about a vector network analyzer now a vector network analyzer is different than the other things that we've used because both an oscilloscope and a spectrum analyzer analyze signals and active pieces of componentry so a vector network analyzer actually is for measuring passive things so no energy goes into this device this device actually generates outputs and then reads back in off of its own output so we don't put any power into this thing or it'll explode or you'll fry it basically and the display is reversed but we'll walk through it but essentially what it's doing is it's trying to read the properties of whatever the cabling or at least generally you can call it a network the thing is that it's connected to it's trying to measure the passive properties of the things that it's connected to pieces that we really care about for RF and specifically for ham radio we care about the resistance because we want everything to be 50 ohms and resistance is actually not a linear thing in terms of RF it actually has capacitance can add resistance and so can inductance which is where you use a copper or a toroid type thing a coil sort of less common in DC circuits but a coil also causes resistance and can change the resistance equation of the thing so this circular chart here is called a Smith chart and right here is 50 ohms no capacitance no inductance and you have to calibrate your VNA with a bunch of tools or with some passive component tools actually have them here so there's a there's a short and open and a 50 ohm load and you use those on your ports here to calibrate your 50 ohm starting point so the Smith chart the resistance this green line on mine will move around and it usually will loop and go up and down and come back and forth and we want to keep that close to the middle and close to this point right here which is where it's set at 50 ohms the other useful things we can get out of this is the log mag so this is essentially the permeability so it's sending out a signal and how much of it is coming back so a resonant antenna on a certain frequency all of the signal that you send out to it none of it should come back if you're sending out that frequency and related to that is SWR which is what is the magnitude of what's coming back so these two are quite perfectly but almost inversely related to each other so what these are used for is measuring antennas especially for building and tuning antennas and getting them to be the most efficient for where you need them to be and so we're going to look at some antenna components here so this is a 9 to 1 ratio commercial product this is the LDG antenna so this is an NFED long wire antenna or NFED random wire so the signal comes in here and then it does some basically transformer loops like you would think of like a power transformer but it actually goes short right back to ground after it goes through the loop a few times and this may look really weird to somebody who works on DC circuits but on AC there's enough resistance there that this actually is the desired pattern so the majority of your signal is going to come out through it's faded because I had it out in the sun but essentially this red port up here this black port is for a counter poise which is not always used for a antenna but it's useful for helping tune it in the field so what we're going to do is I'm going to hook this up and I've actually just attached literally a random wire this is some harvested cat 5 twisted pair wire I have no idea how long it is I have no idea what this is going to resonate at or what the properties are so we're going to take a look and hopefully it's interesting so I'm going to put this on here and so here we go we can already see some interesting bits how far am I looking I've actually got a pretty wide range here across the handband and across most of the way it looks like our SWR is about 2 and we're not actually emitting much signal here though so this is wide banded but still terrible and our resistance you can see we're getting at the point where the thing is right now we have 70 ohms and 520 530 picofarads so capacitance our antenna is actually capacitive right now so there's a few ways that you can combat the capacitance you can actually add more inductors, more turns to your toroid here we'll sort of bring that back up but another thing here is that most people don't realize is that the ground is actually very capacitive so if I actually just pick this up off the ground and hang it on something maybe I can reduce the capacitance that way so yeah you can actually see it reduced a little bit so the so you can actually see how sensitive some of this stuff is so the touching antennas moving them around actually changes a lot of their properties even touching this I'm adding capacitance to the circuit your body is capacitive that's why capacitive touch sensors work but we're actually only going up to 15 megahertz which in the grand scheme of RF is pretty low so we're going to go we're going to change the stop marker I'm going to change this to just change it to like 200 megahertz and we'll see if we see anything more interesting here and wow okay so that looks a lot different so you can actually see the so you can actually see that the resistance goes all over the place and this is the usefulness of the Smith chart it's actually going at various frequencies it's actually going from capacitive to inductive and you can actually see that there are some interesting resonant points here especially over here right here and right here and I'll figure out where these are this is a touch screen but it's not the best touch screen so somewhere around 36 megahertz 35 36 megahertz there we go now we're in the hole 34.9 megahertz has a spot where we actually are getting 22 dB of gain on the release of the antenna so it's actually emitting right there and the SWR actually drops to 1.1 to 1 which is really good so right at 34.9 something megahertz this antenna would work great or it seemingly would work great the orientation of it on the ground because I have it just laying down probably actually wouldn't work great so then this is another point right here at 176.420 megahertz and we have similar drops our SWR doesn't go quite as low and we don't have quite as much gain on the antenna but it would probably work here almost as well as it would over there so this is me touching it actually if I let go of this it might completely change the properties it's not terrible ok it did change it a little bit it actually made it quite a bit sharper on this first one I can't quite get it in the hole so it actually made the SWR drop almost to 1.0 and this one actually looks a little bit sharper a little bit deeper so it's 1.2 SWR here you know this is a rough measurement like you can't necessarily trust exactly the numbers on here but they do give you a pretty good indication and they're actually more than accurate enough for amateur radio purposes and for most non-commercial purposes as well so as you can see the antenna itself is very sensitive if I start moving the wire around I'm just going to mess with it a little bit it totally changes the graph hopefully that's still showing up I know there's some glare in here ok so it totally changes the graph and then me touching it of course totally changes the graph as well it's important to with the VNAs to get yourself set up in a situation where you can not have to touch the actual devices which is actually a lot of the challenge so when you're creating an antenna let's say you're making an antenna from scratch you actually want to set it up in such a way that it's going to be exactly where it's operating or in similar conditions to where it's operating so if you're doing a field antenna you want to set it up on the ground basically or in the manner that you're going to be using it in the field so similar heights, similar environments around it and then start tuning it because otherwise it's not going to work the way you think it is in the field and so for the last demo I've got my helper with me we're going to build a 10 meter dipole and we're going to use the VNA to make sure that it does what I think it does and actually real quick before that let me just show you when you're making a dummy load not all dummy loads are equal so let's take this off of here and we're going to stick this guy on here so you can actually see that even though this should be calculated to 50 ohms depending on where you are frequency wise it doesn't actually do very well alright so I lost a little bit of video because I ran out of space but what we were seeing was the this larger dummy load is actually not very consistent, it's not very good but if we look at this smaller dummy load that I made right here it actually looks very good at least in the handband range and let's see if I extend the stop part out to 200 megahertz let's see so it's actually pretty good across the board you can see the SWR is basically the I'm going to set it up closer, I can mirror this one a little bit the see if that shows up, yeah the green resistance stays pretty much centered so we're not very high in inductance or in capacitance we can actually see what we got, it might be hard to read but we've got a couple nanohenrys four nanohenrys of inductance here the log mag is straight across the board and the SWR is basically perfect across the board now this can't handle very much in terms of power because you'll just melt these little quarter, I think these are quarter eighth watt resistors but this works very good for testing small radios that don't put out a lot of power or if you can attenuate it even more before it gets to the dummy load, that will also work okay I think that's it for the V&A on the bench but let's go outside and build a simple dipole antenna and we'll use the V&A to set it up the way that we want alright so we're out in my backyard trying to get everything in the shade but what we're going to do is we're going to look at two different antennas one is I'm going to make an inverted V-dipole out of this B&C binding post connector and some cheap craft 26 gauge wire and we're going to look at that versus vertical adjustable antenna this is a commercial antenna, it comes from a company called super antenna and we're going to use I'm going to adjust this, we're going to use the V&A to adjust this and we're going to 10 meters the same thing I'm going to build this dipole with and then we're going to compare what they look like and also show you the difference on a radio you can see what's going on here and you see the effects alright so what I've got here is I've actually got this B&C binding post with the wires connected to it and I've got that connected to the V&A if I could get this back on here the one of the things you'll notice is I switched everything to B&C so I put adapters on things just because I found that B&C tends to be a lot more forgiving in the field you don't have to worry as much about breaking them and things like that so let's see if this shows up, there's a lot of glare out here and there's so much glare okay so we've got I've got this way zoomed out so you can see more characteristics, 10 meters is really not the best to show some of the characteristics of these types of antennas but generally a inverted V antenna will have a pretty broad usability band where the SWR is low enough and I've zoomed way out to sort of show and if I zoom into the whole 10 meter band the whole 10 meter band will be under 1.5 to 1 at least when I was messing with this a minute ago, but the antenna itself like I said is literally just wire through the B&C and all I've done is I've actually untangled myself I've actually started with the wire long and I've wrapped it up around the rock to change the to do two things, one to plant it to the ground so it stays still and two if you make a coil at the end of a wire it actually electrically shortens the wire and it'll appear as the end of the antenna or the end of the wire to the antenna or to the network so this is actually very useful for adjusting antennas in the field or when you're getting ready to cut them or whatever always start long and then roll it up on something and cut it further once you know where you want it but I've done this exact thing in the field and it works fine not on a 10 meter antenna this is a little bit low to the ground for an inverted V this is a bit low to the ground but this would work if you were on top of a mountain like doing a soda or something like that and what I actually have is I have a 6 meter pole that I put wire antennas off of out in the field it's like a fiberglass pole and you just string it up put your thing on top of the pole and push it up and that becomes your antenna in the field so that's really all there is to it for building a die pole antenna there are two pieces it always has a ground plane which comes off of the shield of the cable and an active plane which is the center pin of your of your coax, the center pin of your antenna setup and even in a vertical like this one right here this entire upper part is the active piece and the lower triangle see if that shows up so the lower tripod stand here this is actually part of the ground plane and this interacts with the actual ground and we also have some radials cut to specific lengths coming off of here and so a lot of times on a vertical antenna where you have your active element going vertically you'll have a whole bunch of radials on the ground to create a better ground plane for it so let's take a quick look it's set up it should be set up for 10 meters I'm going to take this off of here for a second and I'm going to put this on to this antenna so now we're measuring the other antenna and I didn't change the zoom at all here let's see if that shows up so you can see that the dip is in a little bit of a different place so this antenna is electrically shorter because the dip is higher when you're measuring the antennas a dip to the left at a lower frequency means the antenna is long a dip to the right to the side means the antenna is short for your target frequency so you want your dip to be right on your marker on your frequency that you want this antenna has a narrower bandwidth this doesn't show as much on 10 meters because this antenna is actually a significant portion a significant size of the 10 meter band we're not actually using a lot of the loading coil so I'm going to actually take a second and set it up on a lower frequency higher wavelength so that we can see some of the properties of the vertical a little bit better alright so now I've got this vertical set up for 20 meters this has a sliding coil where the upper element touches the coil in only one place and you can slide that up and down for the connection it works pretty well but the main property of a loaded vertical like this has a very narrow bandwidth like what I was saying so now I have it set for 20 meters you can see how narrow and how deep that piece is versus the 10 meter portion up here it was very wide and flat I have not changed the zoom level at all so this is the same scale that we were just looking at but that is very common just because I'm touching the VNA but if I touch the antenna you'll get similar activity on the VNA so you measure this with everything sitting down and you don't touch it but you can see how narrow that bandwidth is compared to the wide bandwidth that we got from the inverted V and this is typical of a vertical except this is at 10 meters it's very close to actually being a wavelength of 10 meters without being loaded now let's compare what this thinks the SWR is to what the radio to what a commercial radio thinks the SWR is now I've got the radio tuned to the somewhere in the 10 meter band it's not super important because we're only going to put out about less than half a watt right here and we're very low to the ground so I'm not super worried about interfering with anybody and I've got the radio in Morse code in CW mode so I can push the button and we can send tones and we can see what the SWR is the SWR that the radio sees on the antenna right now I have it connected to the vertical antenna and it's tuned for 10 meters and so hopefully ok so what I'm going to do is I'm going to transmit and we can see that there's no SWR so it's basically thinking that this is a perfectly good antenna this radio is pretty robust it's a field radio so it's pretty tolerant but every radio has a limit on SWR that it will transmit at so now I've gone and I've just changed the coil position on the antenna to somewhat randomly I know it's below where the 20 meter sits so it's not on a harmonic of 10 meter so we're going to try and transmit again and now we can see the SWR there's over 3 points something to 1 so that's probably way higher than you would ever want to transmit with it's not going to break the radio the radio might actually reduce its power around that level anything higher than 2 to 1 is probably not spectacular especially for low power radios you want to get all the power out into the atmosphere that you can so real quick let me I'm going to swap this over to the vertical here and if you remember the V&A showed 1.5 ish to 1 on both of these antennas but the radio actually only showed it as 1.0 to 1 are almost perfect so they're not perfectly in sync with one another and I don't necessarily know which one is better at measuring but the radio is the one that has to make the decision in the field so if you can measure it with your radio after the fact that's always good too so now we're hooked up to the inverted V and I'm going to send this should be around 10 meters so we have a little bit over let's see if that's showing up a little bit over 1.0 to 1 so this is probably 1.2, 1.3 to 1 which is still perfectly fine for transmitting at and we can adjust it roll up one side here and you can see hopefully we can observe that the SWR changed hopefully that was enough of a change it's actually better now so it's showing up as 1.0 so let me go the other way I rolled it up, I made it shorter I made it about 10 inches longer so there we go so now the SWR is closer to 1.5 to 1 that looks like it's showing up so that's a quick demonstration of tuning an antenna adjusting an antenna with the V&A and then double checking it with the radio so we know that they're at least pretty close together if the V&A is showing that it's in the low 1.x SWR it's probably pretty close to 1.0 or 1.1-ish for the radio which is good, that's where we want it we'll do the waves bouncing back into the radio if we can help it alright thanks for joining me on this talk I'll be happy to answer any questions in the Q&A session or online, you can find me on Discord and all sorts of other places but we'll have links in the video description I imagine please feel free to reach out to me and I'm happy to talk about any of the things that we've discussed and any of the tangential stuff that you may have questions on so thanks again for watching