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):
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:
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.