DIY Doppler Speed Radar from Satellite Dish LNB - Microwave Radio Electronics

this is going to be a quick video showing how I took a satellite lnb from a DirecTV satellite dish and repurposing it as a speed measuring radar this particular unit here has three feed horn sections tip it covers off of these two just so you can see what's going on this is the section that I modified to make it work as radar I'm going to give you a quick overview and then I'll do a demonstration showing how it works this feud or in section here and this one here are symmetrical so I'll show you this one for demonstration purposes what's going on is there's a circularly polarized so these two antennas here one is for the right-hand one is for the left hand and there's a stair-step septum in the middle that splits the wave the incoming wave and it's pretty simple it's basically a series of low-noise amplifiers and then there's some I believe they're called edge coupled these are these abandoned as filters right here and some more amplification and there's a dielectric resonant oscillator there's actually two of them on this one there's a ro here there's one you can tell the telltale sign is a little set screw that to adjust it and that comes out of a BJT and that BJT goes to a pretty simple diode mixer right I'm I'm pretty sure it's the diag mixer I can't really tell it's all citrus poncy so the one dro is here the other ones underneath here and there's a some coax that connects it on the back of this PCB all the way up to here so what I did was on this this one here which I'm not showing you but I took the transistors and I rotated them 180 degrees so the gate was where the drain is and then the drain was where the gate was and then I just caught a couple traces and soldered a couple things so that the biasing circuitry is connected properly so that bias is a gate and drain so that they're mid rail basically on the 12 volts that I'm powering this with so basically what you end up with is a sign of capable of receiving and then a side that's capable of transmitting and this is on the 10 gigahertz range which is the k a k u band actually and I have the receiving the receiver of this one here coming out it comes to a DC blocking capacitor and it goes underneath the shield here I have that on this red wire here so I'm going to hook that up to my oscilloscope and that's getting mixed with the gr oh and there the local oscillator so what's happening is I have one side one antenna of this feed horn right here transmitting roughly at 10:00 or 11:00 gigahertz output does just directly from the local oscillator and then that's bouncing off of an object and then when it comes back the only pulses that I get out of this red wire here will be the difference of those so I will get a small pulse on here in the millivolt range when we have a difference in phase between the signal that's coming out and the signal is coming back and that's basically the premise of Doppler speed measuring radar so I'm going to get up to power and my oscilloscope then will give you a demo these can be powered off of anywhere between about 12 and 19 volts they're not very picky and actually you can select the different polarization either the left hand or right hand if you vary between 13 or Nike and volts in this experiment it really has no impact on what's going on so I'm going to power about off of the powered off about 13 volts I have my power supply here so to supply the power just your standard F type coaxial connector and you can pick any one of the little connectors on here I have 50 ohm terminators on our 75 ohm terminators rather I'm the ones that don't need so hooking that up so that gets power and then this red wire is going go to my oscilloscope it's powered up and hooked up to the oscilloscope in the top right corner right there as you can see when I put my hand in front of a few Tarn you'll see spikes in the output there and that's what we're using to measure so all we have to do is put an object in front of the feed horn here move it towards the feed horn at a known rate and then measure the frequency of those pulses that are coming out of the mix output of the mm B then we plug that into an online calculator because I don't want to do the math myself and that'll tell us the speed so I calculated out that one mile per hour is about 17 inches per second so the feet horn is right here and then 17 inches after that I have this as a barrier basically to reflect the signals back into the lnb here and it's very imprecise it's just a rough group of concept right here I have no I might be better look at that this is just so I can keep time this is a frequency generator set to generate one hurt so I'm just going to kind of do this by hand I'm going to hit trigger on the oscilloscope trigger basically capture for about five seconds and then I'm going to move this closer to the lnb so that when the needle hits zero and when it's one this has moved to 17 inches so it's very rough and very imprecise but we should get a result there about 1 mile per hour so I have my finger on the single capture from the oscilloscope and I'm set to capture a 500 millisecond for a division so that's going to be about five seconds or rather two seconds for the entire capture and I'm going to move the object closer to it in time all right and here's the waveform that we got this is the interesting part which has our pulses so I'm just going to zoom in a little bit and let's slide over to that so those are my pulses I'm going to open up some cursors but one cursor on one pulse put the other on the other and we're going to get a frequency in Hertz so one here all right and like I said this is very imprecise it's just an estimate but it's it will be a good proof of concept and as you can see the frequency 8 I got here is thirty point eight six we'll just say three point nine Hertz and I found there a couple good websites to do this one of them was hyper physics PHY - a STR GSU edu if you just search for a speed measuring radar calculator this should come up you have to enter the transmitting frequency in my case I'm pretty sure it's about twelve point two five gigahertz sorry 11.25 you get Hertz I have no test equipment capable of measuring that so we're just going with that it's not too sure about that and then I enter in the beat frequency in this case the term beat is the difference is frequency one - frequency - where frequency one is the transmitter frequency frequency two is what's being received so it's going to be that phase shift those pulses are going to be how often we're getting that phase change and we said that the one while this experiment was thirty point nine Hertz and when I hit enter we'll see that the speed in miles per hour is 0.92 miles per hour and the way this is laid out is kind of misleading the meters per second is this value here miles per hour here kilometers per hour as this value and feet per second is this value so we measured 9.2 miles per hour which is very very good considering I was moving an object by hand without a proper timer and we don't even know the correct local oscillator frequency on this so I'm overall quite pleased with that result and I'm looking forward to doing some more cool experiments with this lnb it's a microwave electronics are really really fun and it's not too difficult to get into because these lnbs are so cheap so you really can get into playing with this stuff for less than $25 or so you just need some decent tests will come in so thanks for watching and I'll see you next time I forgot to show you the modifications I made so this is to the first feet horn which I made the transmitting modifications to I used a video by Jeri Ellsworth for reference on this that was a very big help I probably wouldn't have been able to do it otherwise so I'll put a link to her channel to some really really interesting stuff what's going on here is this is the unmodified receiving side and there is a transistor some filtering and a bandpass filtering so this is just a vacation and then it's coming out the right here and that's where I'm measuring it this chip here is responsible for biasing the transistors well they're they're not bipolar they're more Vasilis these are RF specialized fats I'm not exactly sure what kind of fat they are and there are two fats one here one here that I using a rework station I took those off and flip them and then I had to play around and figure out what traces to cut and just swap around the biasing circuit sure it wasn't too complicated at all and then there's a third transistor here that is not necessary that should be removed because that's the final amplification before that would get mixed but this channel is not supposed to be mixed so instead of that we're just connecting right to this transistor here from the local oscillator the Dro is right here then on the backside of this there's a piece of coax here's the solder point here and then it ends up right here then that gets amplified this is just another FET and i'm coupling that negative two volt oscillator ish through a I don't know it's like 100 Pico farad or so I really don't know the exact but I just kind of grabbed it so I'm coupling that through a ceramic cap all the way over here to this point here which is the gate of a transistor or a FET rather and then the drain of that is going to the gate of another FET and then the drain of that FET goes to an antenna here so that's it it's really not that complicated at all even though this thing looks really crazy and got cool patterns on it and stuff in case you're wondering how to do the math without my calculator and the formula is pretty simple you can just do velocity is equal to the change in frequency or which is that beat frequency and that's equal to the absolute value of the transmitted frequency minus 3c frequency times the wavelength and in our case the beat frequency was about 35 Hertz and the wavelength of 11.25 Hertz is 26 millimeters and then you divide that by 2 and in our case that's pretty simple just take the 35 Hertz multiply that by the wavelength 26 millimeters I might put the milk put that into inches by multiplying by 0.03 937 o 7 8 7 divided by 2 millimeters per set or inches per second rather multiple or multiply that divide that by 12 by the PI 5200 280 and then multiply it by 3600 and we get one mile per hour

Channel: Sam Zeloof

Views: 54,403

Rating: 4.8733029 out of 5

Keywords: diy, electronics, microwave, radio, radar, doppler, lnb, satellite dish, arduino

Id: kxoOVR-8Wwc

Length: 12min 11sec (731 seconds)

Published: Sat Sep 24 2016

Reddit Comments

[u/RF_engineering_Man]

Cool stuff. Nice video! I've been meaning to mess around with an LNB for a while now.

[u/scompa]

Very interesting, this is really cool. I have been curios about microwave electronics for a while so my question is: how did you get into it?