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From: | Marcus D. Leech |
Subject: | Re: [Discuss-gnuradio] Newbie question on USRP2, synchronization done by the FPGA? |
Date: | Wed, 01 Sep 2010 19:57:06 -0400 |
User-agent: | Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.11) Gecko/20100720 Fedora/3.0.6-1.fc12 Thunderbird/3.0.6 |
On 09/01/2010 06:47 PM, Sam Keene wrote:
I'm not sure what you're asking for, but I'll take a stab at guessing :-) I'll describe what the USRP2 does on the receiver side: o Complex samples the input (which is complex, that is I + Q, baseband, typically) at 100Msps o Filters and decimates that complex sample stream down to whatever sample rate/bandwidth you wish to appear across the 1GiGe interface (and hence into your Gnu Radio application). Your Gnu Radio application then does whatever it does with than complex-sampled stream. That stream is a time-series with fixed and uniform timing, so any discrete-time-series "math" you want to do on that stream will "work". o Both the sample clock and synthesizer clocks can be synchronized to an external source, via the 10MHz SMA inputs, or via the so-called "mimo bus". o The FPGA "assists" in the programming of the various daughter-cards programmable elements, like the PLL synthesizers and variable-gain elements in the gain chain. The transmit side is the logical reverse, with the D/A sampling at 200Msps, and the FPGA interpolating your application data stream as appropriate, and presenting it as a complex sampled baseband stream to the D/A. From there, it is presented to complex mixers on the daughtercard to produce the desired final RF signal. I don't know if this even comes close to answering your question. -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org |
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