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. > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
