# Passive radar using my hacked dual coherent channel rtl\_sdr dongle **URL:** \ **Category:** GNU Radio\ **Created:** [September 26, 2013, 12:24am UTC](https://www.ruby-forum.com/t/passive-radar-using-my-hacked-dual-coherent-channel-rtl-sdr-dongle/236696 "2013-09-26T00:24:56Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [September 26, 2013, 12:24am UTC](https://www.ruby-forum.com/t/passive-radar-using-my-hacked-dual-coherent-channel-rtl-sdr-dongle/236696/1 "2013-09-26T00:24:56Z")
I hooked up my dual coherent channel rtl\_sdr dongle into two of our passive radar antennas that we have here (log-periodic antennas pointing North and South). After fine tuning gains and signal levels, I acquired some FM radio data (WWLI 105.1 MHz). To my surprise, I got passive radar echoes from airplanes when I analyzed the data. Passive radar is one of the most challenging types of radar because the requirements for dynamic range are larger than those for eg., pulsed radar, I really didn’t expect much from my test. I expect the $16 system to also be able to see specular meteor echoes (typically stronger than airplanes) and ionospheric field aligned irregularity echoes. Not bad for something that required about $10k-$100k investment in a digital receivers ten years ago, and a $2k investment yesterday. Visually, the rtl\_sdr dongle system has a little bit more noise than the usrp n200 with a tvrx2. And also, there is the hassle of aligning samples. So I would still use the usrp if given a choice, as it does perform better and requires no hacking. Here is the passive radar video I just made using my $16 dual channel rtl\_sdr (the timestamp is broken, but I just did the measurement an hour ago): [![](https://img.youtube.com/vi/KRqtqtCVRR0/maxresdefault.jpg "FM radio passive radar using a hacked dual channel rtl sdr dongle array") ](https://www.youtube.com/watch?v=KRqtqtCVRR0) For comparison, here is an example passive radar video of airplanes and specular meteor echoes done using a usrp n200 + tvrx2. This was earlier, so the targets aren’t the same: [![](https://img.youtube.com/vi/-k2ZuhAz0ac/hqdefault.jpg "FM Radio Passive Radar, WWLI 105.1 MHz") ](https://www.youtube.com/watch?v=-k2ZuhAz0ac) Does anyone know who manufactures these dongles, or who designed it? PS. I ordered a seven port usb hub, in anticipation of adding more coherent channels (to do interferometry and maybe imaging). It seems that every time I browse ebay, I end up ordering a few dongles. juha ---
**Author:** ![Juha\_V](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/4af34b/32.png) [@Juha\_V](https://www.ruby-forum.com/u/Juha_V)\ **Post date:** [September 26, 2013, 3:01pm UTC](https://www.ruby-forum.com/t/passive-radar-using-my-hacked-dual-coherent-channel-rtl-sdr-dongle/236696/2 "2013-09-26T15:01:38Z")
This is awesome. How did you analyze the data ? Is the software/source (both grc setup and data analysis) available ? Mark ---
**Author:** ![Juha\_V](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/4af34b/32.png) [@Juha\_V](https://www.ruby-forum.com/u/Juha_V)\ **Post date:** [September 27, 2013, 3:22am UTC](https://www.ruby-forum.com/t/passive-radar-using-my-hacked-dual-coherent-channel-rtl-sdr-dongle/236696/3 "2013-09-27T03:22:08Z")
Hi, I’m just using a simple script to dump data to disk. I then have another program that analyzes the files. It is not too complicated. The measurement equation is a convolution with the assumption that the target is stationary over ~20 ms and that the ground clutter is stationary over ~1 second. My code is a mess at the moment and it depends on other unpublished libraries that I have written, which are also a mess. I might release this once I have cleaned it up a bit. juha ---
**Author:** ![Juha\_V](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/4af34b/32.png) [@Juha\_V](https://www.ruby-forum.com/u/Juha_V)\ **Post date:** [September 27, 2013, 5:28am UTC](https://www.ruby-forum.com/t/passive-radar-using-my-hacked-dual-coherent-channel-rtl-sdr-dongle/236696/4 "2013-09-27T05:28:56Z")
Since they’re clocked together I would assume that your alignment would consist of interpolation on the primary FM signal, what do you do to remove it later? If your code is too messy to release can you share a block diagram? Thanks, Jared ---
**Author:** ![Juha\_V](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/4af34b/32.png) [@Juha\_V](https://www.ruby-forum.com/u/Juha_V)\ **Post date:** [September 27, 2013, 8:17pm UTC](https://www.ruby-forum.com/t/passive-radar-using-my-hacked-dual-coherent-channel-rtl-sdr-dongle/236696/5 "2013-09-27T20:17:18Z")
On 09/26/2013 11:27 PM, Jared C. wrote: > I just re-did my tests with a pair of synched dongles, and instead of inject RF externally, I just tuned it close to the 2nd harmonic of the clock. That produced quite stable, near-perfect, correlation, once I adjusted the phase to peak up the correlator output. This puzzles me greatly. This implies that both dongles are properly phase-locked to the master clock, and that the leakage is being coherently downconverted, and that no samples are being dropped. So, my phase-coherence issues are with my external RF injection. Which I just plain don’t understand… – Marcus L. Principal Investigator Shirleys Bay Radio Astronomy Consortium > **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org)** > > Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami. ---
**Author:** ![Juha\_V](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/4af34b/32.png) [@Juha\_V](https://www.ruby-forum.com/u/Juha_V)\ **Post date:** [September 27, 2013, 9:50pm UTC](https://www.ruby-forum.com/t/passive-radar-using-my-hacked-dual-coherent-channel-rtl-sdr-dongle/236696/6 "2013-09-27T21:50:12Z")
Cool. I wrote up a few blog posts about the tests I did this week: > **[$16 dual-channel coherent digital receiver](http://kaira.sgo.fi/2013/09/16-dual-channel-coherent-digital.html)** > > I have been playing around with the cool RTL dongles (more on rtl-sdr dongles on  superkuh's web page  or rtl-sdr.com ) that you can buy on... > **[Passive radar with $16 dual coherent channel rtlsdr dongle receiver](http://kaira.sgo.fi/2013/09/passive-radar-with-16-dual-coherent.html)** > > My previous post  describes the $16 dual channel rtl\_sdr dongle hack. In the last few days I've done some more testing and it turns o... PS. I tried adding a third dongle to run with the same master clock. I didn’t do it correctly this time either by using an active signal splitter, as that would increase the total cost :). I’ll hopefully have some more to report next week. juha