Groundplane Antenna for Meshtastic

welcome to my channel and to my video about this particular homemade antenna for mesh tastic and as you can see you'll probably recognize it's a ground plane antenna I'll tell you a little bit about how I made it and how I managed to optimize it to work really well and the equipment that I used to do that one thing which we'll see later on is the um Spectrum analyzer the tiny sa for using the to measure the received signal strength and first of all I'm going to use this the nanovna this one's from C and um we'll use that to measure the SWR one or two people have asked me about how to set up a nanovna um and of course there are plenty of tutorials on YouTube and I've watched a few of them but what I did notice is that um the actual firmware that's in the Nano VNA is quite often quite different different depending on the manufacturer and how official it might be and what version number it's on so quite often the menus are different and and what you see is different so um I'm not going to give a tutorial about how to set this up just apart from quickly to say let me reach for my stick because my fingers are too big for this touch screen um just to quickly say that it's a good idea to calibrate the device before you do anything and I'm not going to do it but I'll just show you where it is you um you have to go and hit the button that says calibrate and different devices have different words in different places so you hit calibrate and then calibrate again and then it's inviting you to connect various things open circuit this comes with it a standard open circuit so you screw it onto the port one the open circuit that's that Port there and then you press the button that says open to tell it that the open circuit's there and then it'll invite you to press the the short circuit button so you put the short onto that Port one press short and then it says load so you put the dummy load onto Port one and press the load button and then it asks for isolation that means nothing connected to any port so you leave both ports unconnected and press isolation and then when you're done you hit done and then I save it so you hit save and then save it into one of the pre-save configs or presets they've got different names on different devices again and what I've done here is I've set up a frequency range of 800 MHz to 1 GHz because that's got the ism 868 band in it somewhere and so to do that you hit stimulus and then start frequency you type in 868 M for megahertz I'm going to go back and then you put in a stop frequency no it wasn't 868 no it's 800 to 1,000 so this will be a th000 m for mehz go back press M and then you set up the 800 to 1,000 you can see there 800 to 1,000 megahertz and I also have one marker switched on and the marker I set to 870 MHz which is close enough to 868 because it goes in quite big jumps when the span is that white and that's the S11 curve or SWR you set SWR in the menu and then it'll display s SWR I set it with one per division which means that when this is yellow lines down at the bottom that's anwr of 1.0 that would be 2.0 3.0 4.0 5.0 going up one SWR unit per division which I think looks okay to use and that's really about it I always check that the analyzers working how I expect by plugging in something that I know like this antenna the modified and tuned halfwave vertical from China for £290 so uh that's been tuned by me to be really resonant at 868 MHz of course it won't be when it's laying down like that we have to stand it up sorry if this is going to go sideways now but now you can see there's a nice dip in the S SWR curve and the SWR reading is 1 05 or so at 870 MHz because I've tuned it so that's a a decent antenna that's matched at the frequency we're interested in and what I'm going to do is connect it to the Grand plane antenna and measure that and this has also been tuned using pair of wire cutters which I can't show you but what I did was I got the rough measurements from a website with a calculator on it there are several ground plane and different antenna websites that that calculate dimensions and they all give slightly different results so I'm not going to say which one's right or wrong it depends on so many factors I'll put the links below to a couple of favorite ones that I use and um what I did was I cut the elements longer than they needed to be and connect them to the analyzer and sure enough it came out too low in frequency and then I enjoyed myself by snipping off little bits on the radiating element watching the frequency of the dip on the S WRR move up the frequency scale on the VNA until I got it to where I wanted it well close because then these radials were too long and what I did was I Trimm the radials down a bit to closer to what the theoretical values were doesn't really change the center frequency really noticeably at all it's really this element which is setting the the resonant frequency of the antenna and I started out with these horizontal and I know they're supposed to be bent down at 45 degrees but what happens when they're horizontal the answer is that the dip you get doesn't go all the way down to one an S swr1 it's it's higher maybe it was 1.5 or 1.8 and um I wanted to experiment because I built antennas like this when I was a teenager in the 1970s and of course we didn't have Vector Network analyzers there was no way of work knowing if it worked apart from using a NWR bridge and Signal reports if you were transmitting so now with the VNA you can see what happen so I started with these being horizontal in a plane and then I bent them down and I noticed that as I did this the SWR improved and got better and better until I reached the optimum value which is that angle which probably is 45° I haven't measured it if you bend them too far the SWR comes up again so um it proves that you do have to pay attention to this angle I always wonder about a quarter wave whip on a car roof because the car roof is flat normally it's not a pyramid shapes I don't quite know about that but let's not worry about that now um so this is the right kind of angle but it's it's good to experiment with these things and all I did was then trim this down a bit more to get it really at 868 megahertz which it is at the moment and works nicely the way I've made it is put it on a piece of plastic drain pipe and the drain pipe has a bung plug that goes in the end for blocking it normally which is a nice tight fit and um all I did was I drilled a hole put a upside down connectors an so239 which is uh not the favorite connector for high frequencies at all but it's all I had in the drawer and I thought why not let's give it a try it's probably a bit lossy um it would be better if this was PTFE in here the white PTFE is is better for high frequencies but this one is a cheap nasty one with brown plastic it's not even bakerite which it would have been in the old days it's it's plastic and it melts if you get it too hot so you have to watch out anyway soldered it together and it seems to work quite nicely so what I'm going to do first of all is measure the SWR of this and then I'm going to do some field strength tests like I did in a previous video so um what am I going to do is disconnect this antenna from here you see how the SWR curve goes crazy when you put your hand near it and I'm going to connect it to this antenna sorry that this is not easy to hold without switching the analyzer off so let's put that on there if you're wearing headphones I apologize for the clunk this is a live video and it's not going to get edited because I'm lazy oh look at that it's resonant at the right frequency 870 is what I aim for it's close enough and the SWR is 1.02 is so um as you can see I spent a couple of minutes just sniffing bits of brass off this is actually made from brass Rod which I got from Amazon not too expensive and it's a bit springy and it's a bit thin probably should be thicker it has nasty sharp ends on it which are very unfriendly I imagine if you get poked by it but there it is and um as you can see it resonates nicely at 870 MHz 1.05 now it depends where I stand and what I'm doing I think if you touch this it might move no it doesn't there are so many variables this is not an an eoic chest test chamber as I said earlier what I'm going to do now is measure the field strength so the way I do that is to use this VNA as a transmitter which is not what it's designed for at all but of course it outputs a signal on this port when and then it's expecting it to come through some device under test back into that to measure the insertion lot so you can check attenuators and filters and stuff but I'm going to use it just as a simple transmitter and the moment it's sweeping from 800 to 1,000 megahertz which is not what we want so what we have to do and I've cheated is to load a preset but what I actually do I'll show you you go to stimulus and then what I do is I set the the start frequency to um 8 69 mahz and then I set the St top frequency also to uh 869 mahz let's just go back of course you don't go back you press M to save it so you end up with zero span so what I'm going to do now is already saved it and it's guaranteed to work I hope so you do recall not preset and then the setting here 869 to 869 so that's zero span so it's just sending out a continuous signal on 869 MHz I think I did measure it once it's not much because of course I don't want to radiate a signal a carrier on this frequency I don't want to jam any other signals but it's very weak um so that's that so it's zero span at 869 and just to check it's actually working I'll connect one of these antennas I'm going to use one of these this is a lyo one which doesn't work quite as well this one works better doesn't really matter so a better match let's put this short stubby antenna on port number one you see immediately it's measuring the S SWR and it's interesting to note that because the frequency span is zero and the frequency is not changing but the display is still sweeping across at whatever speed it sweeps at from left to right what it's actually doing is displaying a curve of s SWR Against Time so the SWR is constant now at 1.6 because it's laid down on the table and if when I put my finger near it the SWR increases of course but if you you do this you can pulse the SWR and get a s SWR Against Time draft which is not something that people normally want to look at anyway that's sending at 869 mahz zero span so I'm going to put this down the antenna test range which is roughly 8 m long I've upgraded the shoe now from a a black one to a white one and that means that it doesn't come up so high the last time was a boot which enclos the antenna a bit so hopefully this is more more light free space so there's the transmitting antenna and then we're going to go back to the receiving antenna being careful not to crash into anything backwards and how am I going to do this I'm going to use this spectrum analyzer the tiny saay which I'm going to switch on usually helps and it's not set to do anything much at the moment and what I'm going to do is I'm going to recall a preset this device calls it the software is very same on both of these I get confused sometimes which one I'm using or I call it by the wrong name so the preset I want to use is 868 to 870 so again you programming the start frequency the stop frequency 868 870 press that and I've also changed this display to be large numbers as an option so I can see them better otherwise it's tiny and that's showing the level of the marker which I've set in the center at 869 MHz plus 3.4 khz but that's to do with step sizes and stuff and you can't get rid of it so it's about 869 so it should be receiving the signal from the transmitter down there which you can't even see so now I'm going to connect what am I going to connect first of all I'm going to connect my favorite antenna this is the one that works by best the home tuned slightly extended halfwave dipole which gives the best normally received signal I'm going to have to hold this still sorry about this put that on there like that and as you can see there is a signal being received what I'm going to do is just move the other antenna the way a bit we hear the stuff on the table so there we are receiving a signal sorry it's going to be sideways so we've got minus 66 dbm what I'm going to do is put it in the place where I'm going to put the other antenna under test and I'm going to try to find the maximum signal strength because as I've said a few times it varies depending on nulls in the radiation pattern so you can see we've got about minus 60 dbm let me just try going higher let just - 70 in the same distance from the sending antenna but different heights of course we get different readings because of all the reflections so this reading is very unscientific sorry about this but relatively we can see what's happening so it looks like about minus 60 fairly consistently minus 60 dbm - 59 and a bit call it on average minus 60 sure I got more last time it maybe I was using a different antenna if you see those other signals jumping around those are other users of the ism band and sometimes my own node here which is just about five meters away will transmit and that makes a huge signal on the right hand side of the peak anyway minus 59.4 I'm sure sure I had more last time this is H how it is but it looks like probably minus 60 is the maximum oh oh I saw a 58 in there always trying to optimize things let's call it minus 59 dbm that's enough so uh what I'm going to do now is connect it to this ground plane antenna using the little pigtail cable there are one or two adapters inside that tube to get it from uh the so239 connector to this smma plug that I'm now putting on the analyzer port number one so minus 59 dbm or so is about the best I got from the other antenna trying to make it so this will stand up by itself not easy doesn't want to okay now I'm going to move this to find a a spot with the most signal it's getting serious I'm going to have to stand up because this thing is quite heavy with this block of wood but it's a useful block of wood so what have we gotus 60 I'm just moving around back forwards up and down there minus 60 there was- 60-ish it's more like- 61 isn't it so I'm still moving it around well there goes my node sending and a few other things- 61 I saw 57 but I think that might be some desensitization being C by caused by the other strong signal so minus 59.4 which is roughly the same as the halfway vertical antenna so um both of these seem to perform fairly similarly in terms of receive signal strength and they both are tuned antennas as you saw with a Resonance of 868 or 870 MHz so the performance is about the same this antenna is experimental which means I can experiment with it what I'm going to do next in the future is to make a very similar antenna but make a disc con because really I wanted to use this this is a a receiving antenna just to listen around in that ISM band because there's quite a lot of interesting signals there and new ones keep coming on every day there's one which I think is causing problems on our frequency for mesh tastic because some people are saying the nodes won't transmit and it may be that when the signal the the channels in use then they they won't transmit and they'll try again well I see that in the serial output so I'm going to look at again I've got um cable to attach the node by the USB speedport to a mobile phone so you can use a Serial terminal app on the mobile phone I'll show you that later and you can see all the Diagnostics and see what's happening so um then I was thinking for General receive I want to receive over a wider bandwidth sometimes so I'm going to make a disc cone antenna to go on here which I've never made before which is a wideband antenna which is not tuned and the SWR should be okayish but over a much wider frequency range and again there's um calculators on websites for making that so there'll be a fure video coming up in the next few days so if you have any questions or comments please leave them in the comments below and suggestions for more videos you'd like to see one person asked me if I could put the transmitter this end and the receiver down the corridor um and that would mean a lot more walking backwards and forwards So my answer is the theorem of reciprocity says that the path loss will be the same in both directions and so the received results should be the same doesn't matter which way the uh the signal is flowing as long as the transmitter hasn't reduced its output power due to a bad SWR antenna which could happen with some radios but I think the uh mesh tastic nodes I've seen don't have any SWR protection in them which is why you have to make sure the antenna's plugged in before you switch it on so um I don't think that the transmit power would change which means that the the path length Link Link budget should always stay the same anyway thank you for watching watch out for the next video and uh remember to like And subscribe if you haven't already by byebye

Channel: Simon Phillips

Views: 6,511

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Id: F4TkF0vs8gw

Length: 19min 30sec (1170 seconds)

Published: Tue Mar 05 2024