On Thu, 2006-06-15 at 02:12 +0200, Martin Dvh wrote: > Eric Blossom wrote: > > On Wed, Jun 14, 2006 at 02:00:27PM -0400, Lee Patton wrote: > > > >>Hi, folks - > >> > >>I'm trying to build an active pulsed radar using GR/USRP. Right now I am > >>only concerned with the transmission and reception of pulses. All radar > >>signal processing will happen offline. I know Eric is working on > >>passive radar. Has anyone tried active yet? > I am also working on passive radar at the moment, not active (yet). > I would suggest using a chirp signal instead of a pulse. > It is much more accurate and power efficient.
Thanks a lot Martin. We are actually hoping to use the returns for SAR. For that we need a lot of bandwidth on scene -- like 100+ MHz. Obviously, this can't be done instantaneously, but it can be achieved via a stepped-frequency waveform. To that end I am using a 13-bit barker coded baseband sequence modulated on a (hopefully) stepped frequency pulse train. I didn't mention this in my email because the stepped frequency adds another layer of complexity that I don't know how to handle right now. I actually pinged the list about this a while ago with no response. http://lists.gnu.org/archive/html/discuss-gnuradio/2006-05/msg00296.html Basically, I need to step the VCO by (hopefully) 10 MHz between each pulse. Since I need this to be correlated with a baseband pulse train provided by another block, I need to do this in C++ (I think) and not Python. It would be very easy to implement in Python, but I never seem to find the easy way :) I'll investigate this once I am transmitting and receiving a pulse train. > > > On TX, the idea is to have a timestamp in the header that says "do not > > transmit before time t". There will be some way to map "frames" > > (variable length things possibly bigger or smaller than a USB packet), > > into something we keep track of across the USB. > It would also be handy to have a feedback-path for TX. > The fpga could report back: > TX packet AAA was transmitted on timestamp XXXX > Then you can also send continuous streams (of packets) and still have exact > synchronisation with RX. > (RX packet BBB was received on timestamp YYYY) > > > On my passive radar experiments. > After doing a lot of simulation I am now trying to do real-world > passive-radar using the usrp and just basic RX-boards with simple standard > cheap FM/TV antenna-amplifiers in front of them. > (I still need better filtering of the FM band) > > I do get signals, but it is probably not an accurate radar image. > If I plot slant-range (the total distance transmitter-object-receiver) > against received phasediff between my two antenna's I get allways spirals. > This would suggest I have a doppler-shift which allways increases with > objects further away which is not very logical. I'm not familiar with this method of slant range vs. phase difference. Usually, I plot range vs. Doppler. I would like to learn more, do you have a reference you can point me to? Do you have range-Doppler images of this data? > If I correlate with different doppler shifts my spirals turn around but they > keep being spirals. > In this image I change the doppler shift in every frame > http://www.olifantasia.com/projects/gnuradio/mdvh/passive_radar/passive_radar_time_is_time_x_arc_is_phasediff_length_is_slantrange.gif > In this image every frame is from samples further in time. > http://www.olifantasia.com/projects/gnuradio/mdvh/passive_radar/passive_radar_time_is_doppler_x_arc_is_phasediff_length_is_slantrange.gif > > Greetings, > Martin _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
