[Discuss-gnuradio] Active RADAR minimum pulse

[Jeffrey Lambert]

Hello to all,

I am working on what approximates an active RADAR for the interrogation 
of a temperature sensitive microwave resonator.  For this project, I 
will be using GNU Radio libraries and a USRP 1 device.  In my research, 
I have discovered some issues that might pertain to this project in 
attempt to use the USRP in a RADAR application.  Among these seem to be 
the lack of synchronization between transmit and receive, issues related 
to coherence with all but the BasicRX and BasicTX daughterboards (and 
for these two boards, coherence depends on front-end provided by the 
user), and a high minimum pulse width due to interpolation of the output 
signal.

With regards to the issue of synchronization, I believe that for my 
application I should be able to work around this problem as I do not 
require precise time measurement.  I do, however, need to be able to 
ensure a particular response can be tracked with the excitation 
waveform.  This seems likely to be simple to implement.  I do not 
require phase coherence for my application, so this is not an issue either.

What I do need however, is to generate relatively short RF pulses.  For 
my application, a pulse time between 10 - 50 ns should be sufficient.  
It seems to me that there is no way to bypass the interpolation that 
occurs during digital up-conversion and thus the only way to operate the 
DACs at there maximum rate is to interpolate.  Can anyone confirm this?

What I am wondering is, could there be some way to create a buffered 
output that can be used to generate a highspeed waveform that is not 
interpolated or upconverted.  For obvious reasons this waveform would 
have to be periodic, but for my application and others like it, I don't 
see the issue here.  Has this been done already?  Any thoughts on how to 
implement it?

Thanks,
~Jeffrey Lambert, K1VZX

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~Jeffrey Lambert,  K1VZX