Re: [Discuss-gnuradio] Could this output be a problem with myHardware or the python codes?

[Eric Blossom]

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