Hey Eric, It is like this. (1). when I am not transmitting anything rather just using the USRP as receiver, I see the environment signal level using USRP_fft.py in oscilloscope mode. (2). When I start to transmit and recieve simultaneously, then the signal recived is the environment signals + the transmitted signal reflected from the target + the signal leaking from the transmitter to reciver antenna.
So, I expect that the signal I receive in (2) should be much higher in amplitude than the one I receive in (1). But, what I am getting while doing this experment is the opposite. Actually,I preffered to transmit and receive simultaneously using the USRP because my target is within a distance of 10meter(I am using the doppler radar for human movement detection). But now because of this isolation problem, I am thinking to Implement my radar as pulse radar such that I will transmit for a very short time then stop transmiting and start recieving, then transmit etc... So, what do you suggest me? Thanks! Bruhtesfa On Fri, Nov 7, 2008 at 3:36 PM, Eric Blossom <[EMAIL PROTECTED]> wrote: > On Fri, Nov 07, 2008 at 11:19:40AM +0100, Bruhtesfa Ebrahim wrote: > > Hey Paul, > > > > Ya! you are correct, the isolation is a problem.But what is curious is > when > > i operate the transmitter and reciever simultaneously,the signal level of > > the reciver decreases too much(cancels out) . If some of the signal from > the > > transmitter antenna is also recived by the reciver antenna, I think the > > signal recived should increase in amplitude, because the frequency of the > > signals sent and recived are almost the same(except the small doppler > > shift). But, what occurs is the opposite. > > > > Bruhtesfa > > You may be overdriving the input resulting in some kind of non-linear > behavior. Have you plotted the received signal? Does it look like > what you think you're sending? > > You say that you are trying to receive a doppler shifted echo. Given > your physical setup (antennas, their pattern and their spacing, the > distance to the object that you expect the signal to reflect from, its > velocity and radar cross section), of the power received at the Rx > antenna -- according to theory -- how much of the power will come > directly from the Tx antenna, and how much will be reflected off of > the moving object? Assume a free space model for simplicity. > > Eric >
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