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.