Quick disclaimer here: I am discussing direct reception of Weather Radar Pings, NOT downloading NOAA maps.
Out of curiosity, I have become interested in receiving US Weather radar echoes as a passive illuminator. I thought it would be easy, but it have so far been unable to detect a signal even with direct line of sight (antenna facing the radar). I have build a biquad antenna tuned to the frequency and pointed it directly at the radar and still no signal. This is a dual linearly polarized radar and I’ve tried both orientations. These US based pulsed radars (WSR-88D or NexRad) broadcast 750 kW peak into a 8.5 meter dish so is there any issue with the LimeSDR at 2.7 to 2.9 GHz? I’ve tried both LNAH and LNAW with and without a bandpass filter (Mini Circuits VBF-2900+ with a pass band of 2.7-3.1 GHz). I’m using gqrz to sample with min/max fft turned on and there is no peak where it should be located. In fact. the band looks surprisingly quite which is why the question to this forum: is it the production LimeSDR USB? The radar freq is 2740 and my center freq is 100 to 500 khz off. I’m able to sample local wifi with this configuration (obviously different center freq for wifi). I’ve sampled upto 50e6 Hz.
Confounding factors for getting a signal: I’m 60 km away, but mapping software says I have line of sight. Lowest sweep elevation is 0.5 degrees, and I’m about about 15 meters above the transmitter so probably not within the dish’s -3dbm cone even at lowest elevation. Full volume sweeps take minutes, but I’ve let the receiver dwell for an hour in clear air aimed at the radar. The radar has a pulse length of 1.57 or 4.5 uS and a pulse repetition rate of 322-1282 Hz (short pulse) and 322-422 Hz (long pulse) so average power is low (~500W range).
So, I’m confused why I’m not seeing a blip at 2740? These radars have an eirp of a small sun so even with their pencil beam signal I can’t imagine not seeing anything with line of site when pointed in my direction. I’m not clear is my problem is on the RF input/capture or the signal process side? If it is signal capture, what are the next step I might take to debug my lack of signal? I can drive a few hours to get closer at a higher elevation to get a true bore sight into the dish. Also, I’ve found much on using passive multi-static radar with dtv/fm and of course there is gr-radar for monostatic radar, but I’ve found little about these big radars as passive illuminators, anybody know of a community, github or other efforts around using the Nexrad signals?