Re: [Discuss-gnuradio] Active Radar

[Martin Dvh]

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.

> 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.

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