Re: [Discuss-gnuradio] Active Radar Hardware

[Lee Patton]

Jason and Daniel -

Thanks for the feedback.  I'll look into PIN diodes.  The reason I
wanted to use a circulator was because it doesn't require a switching
signal to be generated from the USRP.  And, while generating such a
signal is possible, it is difficult (if not impossible?) to ensure it is
timed properly with the transmit waveform -- unless I do some FPGA
coding, which may be the necessary next step. (Again, something with
which I have no experience! But learning new things is fun, right?) I
think I will look into using the actual Tx waveform as the switching
signal. 

Also, Jason, thanks for pointing the need for a variable attenuator to
condition the signal for ADC.  Although I've been aware of this in the
past, I forgot about it in my application.

Thanks again fellas, 
 -Lee


On Fri, 2006-09-29 at 18:15 +1000, Jason Hecker wrote:
> > We make MF & VHF systems and for some of our VHF systems we use a single
> > set of antennas and a T/R switch (passive and active). However since our
> > frequency of operation is 2-3 orders of magnitude lower it's probably all
> > different...
> 
> The radar I worked on was a ~2.7GHz job.  Since the receiver was spammed for 
> the first several hundred metres in range due to large amounts of echo from 
> ground clutter any such early returns were gated out.  After that the circuit 
> controlling the attenuator (PIN diodes) ramped the voltage so that the 
> overall gain of the system increased in time.  This was to maximise or 
> normalise the S/N ratio at the ADC.  When you are looking for metallic 
> bogie's many 10's of KM away you need all the return you can get even with 
> the gain achieved from integrating multiple returns.
> 
> Anyway, the author of the grandfather post doesn't sound like he has too much 
> RF experience (who does?)  Perhaps a circulator will do or even better, an 
> RX/TX switch module (diplexers?) - though this might involve a hardware hack 
> to get the switching pulse out in time.  The thought did occur to me to get 
> something like a Furuno boating radar head with an integrated separate 
> transmit and receive antenna.  You'd get a nice narrow beam from one of 
> those.
> 
> 
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