#188 Antenna Tutorial incl. cheap DIY Antenna Tester (LoRa, ESP32)

everything goes Wireless these days this is why we have a close look at the black magic of antennas how they work what is essential and how to test them based on this knowledge we will build a cheap antenna tester for Laura antennas the same principle can be used to test Wi-Fi antennas pretty youtubers here is the guy with the Swiss accent with a new episode around sensors and microcontrollers wireless systems as the name says have no wires to connect the sender to the receiver they use air instead strange because as we all know air is a very good isolator and does not conduct electricity this is why we have to use radio frequencies instead radio waves travel through the air without problems even in space where there is no air at all but they are quickly stopped by all kind of materials this is why the line of sight is so essential for this technology a wireless system looks like that we have a microchip which wants to communicate with another microprocessor instead of wires it uses Wireless so we have to add a sender and an antenna the space between the two antennas a second antenna and a receiver to replace the wire you see this system is way more complicated than just using a cheap cable fortunately these days the components are inexpensive and straightforward to use except for antennas perhaps they are not easy if we added an antenna to the i/o pins of our Arduino nothing would happen because such low frequencies do not radiate into the air efficiently we have to use much higher frequencies like in the case of Laura in Europe 868 megahertz therefore the sender packs the information onto a carrier on a high frequency this is called modulation the signal with a particular power then travels via an antenna cable to the sender antenna and radiates to the environment and travels towards the receiving antenna the receiving antenna picks up what is left from this power and feeds it to the receiver also via a cable and the receiver filters the relevant signal they modulates the content and supplies it to the microcontroller the whole link only works if the receiver gets enough power from the transmitted signal a send produces power how much usually depends on three things first the purpose of the wireless link its plant reach and its plant capacity second the law because air is a shared area strict rules exist on how to use it and third the energy available in the sending device especially if battery powered for this video I assume the purpose of our system is transmission of data it could also be the transmission of voice or TV signals for Wi-Fi and Laura we use so-called ASM bands for our carriers everybody is allowed to use these bands free of charge without a license but the power of our senders is very limited Laura modules only produce 100 milliwatt or 20 DBM of power as a comparison as a licensed amateur radio operator I'm allowed to use one kilowatt or 60 DBM on some frequencies which is 10,000 times more and even if we would be allowed to use higher power we often do not want because our devices should run on batteries you see we have to pay attention that we do not lose power already before you heard the word DBM in antenna lingo you will often hear DBM or DB ie what is the meaning DB or decibel is a logarithmic proportion it has the nice feature that we can add dB instead of multiplying the values DBM or DB milli watts is used to measure power here is a table which shows milliwatts and DBM let's do an example your sender emits 20 DBM which is 100 milliwatts and your antenna cable has a loss of 10 DB your power at the end of the antenna cable will be 20 DBM minus 10 DB equals 10 DBM which is only 10 milliwatts the 90 milli watt heat our antenna cable and our sender chip will still use the same amount of battery energy apparently the question where can we lose or wind power is essential yes you heard right we can win power in this game or a sort of we will see later how unfortunately it is much easier to lose it as we saw before the first place to lose power is in the cable from the transmitter to the antenna if we use three meters of Archie 174 cable on 868 megahertz we already lose 3 DB or 50% of our power before our signal reaches the antenna the cables delivered with our China antennas usually are thinner and of less quality this is how a good Cox cable looks but they are costly thick and stiff the first rule therefore is use short high-quality and thick antenna cables the antenna has to radiate the power into the space around it antennas only work right on one frequency its resonance frequency in general the longer an antenna the lower their resonance frequency a future video we'll cover how we adjust antennas to the right frequency for today a good antenna transmits all power into the air allows the antenna reflects a lot of the power back to the sender this power again is lost the ratio between total and reflected power often is called standing wave ratio abbreviated SWR or VSWR it is a number between 1 and infinite here is the table rule number two and SWR below - is acceptable and means that less than 11% of power is reflected and therefore lost for our primary purpose a word of caution if you do not connect an antenna to your sender 100% of the power is reflected back to the sender and heats it up this can quickly destroy your small chips rule number three always connect an antenna to the sender now the waves travel through space here the power is reduced with distance if the distance doubles the power is quartered it is quite evident that the power is not only sent into the direction of the receiving antenna no it is sent in all directions you see most of it is lost for our receiver because it never reaches its antenna and here we have a chance to win power if we manage to build antennas which do not radiate evenly in all directions they usually use some reflector to reflect the power sent into the opposite direction towards the receiver this gain is also measured in DB I TBI is the gain of our antenna over an ideal antenna which evenly radiates in all directions 3 DB antenna gain has the same effect as a doubling of the power of the sender if your antenna has a gain of 13 DB ie as this one your sender power is multiplied by a factor of 20 in the direction of your receiver without needing more power from your battery cool it is not clear to me if such antennas are allowed on the is in bands if we run our senders on max power if we reduce the output power it should be okay another important thing you have to know about antennas is polarization if both antennas are vertically or horizontally oriented everything is okay if the two have different polarization you lose power rule number four keep the polarization your antennas the same way if possible also circular polarization exist but it is only used in particular cases like fpv rule number five the more dbi the more directionality of the antenna and the more power in one direction we saw that three meters of RG 174 cable lost 3 DB how does air compare to that I use a simulation tool for this calculation as a simple example we start with a distance of 87 kilometers between sender and receiver the received power is minus 130 DBM how much do we have to increase the range to get a comparable 3 DB loss at a distance of 123 kilometers we get minus 133 DBM 3 DB less so 3 meters of coax cable has the same loss as 36 kilometres in space impressive this is the reason why our small signals travel long distances if we have a line of sight you could watch my 200 kilometer Laura Banford video or read about the 700 kilometres where the sender was placed in a balloon the receiving site behaves precisely the same way a poorly matched antenna or a thin and long cable reduce the already small signal our receivers measure the signal level of this received signal it is called received signal strength indicator or our SSI usually this is a negative number which gets smaller if the signal is weaker because our receiver needs a minimal power or our SSI to demodulate the signal all the effects discussed at up to the so called link budget according to the documentation Laura should have a link budget of 150 DB which is good for about 1000 kilometres with a standard antenna rule number 6 if we do a proper antenna setup the distance in air is not an issue if we have a line of sight theoretically we covered now everything necessary to do a proper set up but how can you distinguish between a bad and the good antenna is speaker really better first we have to look at how much power enters the antenna because if it does not come to the antenna it will not be irradiated as I showed in earlier videos you can use a spectrum analyzer to measure the loss of your cable or the return loss of your antenna unfortunately these are expensive devices and even then it is only under laboratory conditions which can be very different to reality in Amsterdam I met a fascinating guy called Stuart he did a lot of research in antennas for his small satellite which was successfully launched he gave me the idea to use reality to test our antennas and the reality is free of charge and accurate what was his proposal to use one of our law reports as a sender and one as a receiver and place them at a distance we start with whatever antennas on the sender and the receiver and read the RSSI on the receiver side as we learned before the RSSI displays the power which reached the receiver therefore this RSSI includes all effects on the transmitter site like cable and antenna as well as the antenna and the cable on the receiver side to compare another antenna with the one we currently use we make a note of the RSS I leave everything the same and only change the sending antenna now the RSS I should show us the difference between the two setups let's assume we start with sender antenna number one and get an RSS I of -60 then we change to antenna two and get an RSS I of -63 then we know that antenna 2 is three RSSI worse than antenna 1 and because the RSSI is also measured in dB we know that antenna 1 is 3 DB better than antenna to without spending a lot of money I did some measurements in the lab to confirm that the RSSI reading is exact it works fine next we tested the concept in reality as you can see it was still winter here and my partner had to dress up like an Eskimo but we were able to prove that the concept did not only work in the UK but also in Switzerland you should know that I liked the RF part of Stuart's concept a lot but not the part that I or my partner had to run forth and back between the sender and the receiver to exchange the RSSI readings so I added a return channel to the devices the sender now transmits a JSON string with its used power level to the receiver the receiver adds the RSSI and sends the string back to the sender in a later phase both will get a GPS receiver to calculate the distance because the Chasen string includes the sending power and the RSSI the ESP 32 on the sending side can calculate the link budget and display it if we zero the first antenna we get a reading of minus 3 for the second one without running forth and back and in real time this is precisely how I like it of course we average five measurements to get a bit more position we Swiss cannot otherwise because the weather is better now we do not need to dress up for our tests and our devices are also dressed in cute boxes we placed the receiver on a pole about 100 meters away and the sender on this would stick if we start the test by pressing a button the sender waits till we get out of its proximity beeps and - its thing then it beeps again and we can check the result humans around antennas are not suitable for measurements for our first test we use a tuned 868 megahertz antenna and press the zero button this is now the reference I will show you in a later video how I did this tuning next we use a second antenna which looks very similar we measure - 2.2 dB this is the proof that a proper antenna calibration can help the next antenna is built or more precisely printed by me it is called mocks on antenna and should have some gain and therefore also a directivity let's check hi directed towards the receiver and measure 5.2 DB compared to our reference if I turn the antenna in the opposite direction the reading is minus 3 DB exactly as expected for clarification I reduced the transmitter power for these tests to respect the law next I use a longer antenna to check the rule of thumb longer is better unfortunately the performance of this long antenna is much lower than the one of the short as you see in the table next we measure this tiny antenna which was used for my world record it shows minus 0.6 DB we can consider it the same as the reference and now as a courtesy for my friend Richard a ground plane without plane compared with a real ground plane with 4 radials the ground plane without ground was at minus 2 point 2 and the ground plane where the ground was at plus 1 point 4 a difference of about 3 DB summarized we discovered 7 rules rule number 1 use short high-quality and thick antenna cables rule number 2 and SWR below 2 is acceptable and means less than 11% power is reflected and therefore lost for our primary purpose rule number 3 always connect an antenna to the sender rule number 4 keep the polarization of your antenna the same way if possible rule number five the more dbi the more directionality of the antenna and the more power in one direction rule number six if we do a proper antenna setup the distance in air is no issue if we have a line of sight and rule number seven longer is not always better smarter is better as set in one of the next videos I will introduce you to the world of vector network analyzers and show you how you can optimize your antennas it will not be as cheap as it was today but also not as expensive as you might think stay tuned I hope this video was useful or at least interesting for you if true please consider supporting the channel to secure its future existence you find the links in the description thank you bye you

Channel: Andreas Spiess

Views: 149,154

Keywords: tutorial, lorawan, LoRa, ESP32 TTGO LoRa, arduino, antenna, TTGO, RFM95, esp8266, LoRa antenna, ESP8266 datasheet, cheap, diy, antenna tester, Wi-Fi, ham radio, ESP32 datasheet, ESP32 ttgo, eevblog, esp32, electronics

Id: J3PBL9oLPX8

Length: 18min 38sec (1118 seconds)

Published: Sat Mar 10 2018