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Re: [Discuss-gnuradio] Re: Pulse-doppler RADAR wind profiler project an


From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Re: Pulse-doppler RADAR wind profiler project and how to bypass interpolation, DAC filtering, etc.
Date: Tue, 24 Feb 2009 08:17:39 -0800

On Mon, Feb 23, 2009 at 7:53 PM, Nick Withers <address@hidden> wrote:

> Yes, certainly feeling a little overwhelmed!

You wouldn't be the first.

> At this point, that's pretty well what I want to do. I want to smack as
> much as possible in the FPGA (well, on the non-PC side of the USB,
> anyway) and essentially only transfer configuration information and
> returned base-band samples to / from the PC.

For the reasons I mentioned, then, your are better off with the USRP2.

>> Furthermore, depending on the range resolution you need, the 8 MHz of
>> passband bandwidth that the USRP1 can transport over the USB may not
>> be enough.
>
> Should be plenty, I think, given that I want to throw baseband samples
> back to the PC... But I may well be missing something here!

You need to calculate the overall data rate that needs to be sent to
the host, which depends on your PRF, baseband sample rate, and range
gate duration.

> As I understand it, I should be right with timing if I do "everything"
> on the USRP... No? I'm going to need to do some work on ensuring
> pipeline delays between the FPGA and the RF world are configured
> properly...

Yes, but it's not a big deal.  The bigger issue I encountered was
accounting for the turn-around time in the transmitter power amplifier
and antenna switch.  It was almost a microsecond after the end of the
chirp before the PA sensed the end of the power burst and switched to
receive.  This limited the minimum range to a few hundred meters.

>> You can use state machines to handle sequencing of TX and RX, and with
>> the Spartan3 multipliers, you can even do de-chirping or
>> cross-correlation of your receive waveform before it gets to the host.
>
> This would be good, yes. I'm currently fiddling with the Altera IP
> (soft) multipliers, which would I imagine allow me to do this...?

You will run out of room very quickly with the USRP1 if you use these.

Johnathan




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