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From: | Matt Ettus |
Subject: | Re: [Discuss-gnuradio] USRP2 LFTX maximum real baseband bandwidth? |
Date: | Thu, 25 Feb 2010 10:12:55 -0800 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.7) Gecko/20100120 Fedora/3.0.1-1.fc12 Thunderbird/3.0.1 |
On 02/25/2010 01:01 AM, TANGUY Philippe wrote:
Hi all, I would like to send a real signal with a bandwith from DC to 25MHZ thanks to the USRP2 and the LFTX daughterboard. So, I generate a Real baseband signal and I use only the "I" channel. But, it seems that the minimun interpolation of USRP2 is 4 (USRP2faq) that's why I use interp=4. So, I have a bandwidth of 12.5 MHz because the sampling frequency is fs=25 MS/s ==> fs/2 = 12.5 MS/s. For me, it seems good.
If you want a 25 MHz wide signal (0 to 25 MHz), then you should generate it at baseband (+/-12.5 MHz), and have the digital upconverter in the FPGA upconvert to a center frequency of 12.5 MHz That will give you 0 to 25 MHz coverage.
So, my first question is: Is it possible to use an interpolation of only 2 to have bandwidth=25 Mhz?
Using an interpolation of 4 gives you a bandwidth of 25 MHz. Using an interpolation of 2 would give you 50 MHz, but would require 8 bit I and Q samples.
Secondly, I'm not sure but if we use interp=2 we have before the DUC a data rate = 50 MS/s * 32 (float32) = 1600 Mbits/s ==> > Gb/s. However, if we use interp=2 and "short" format, we have a data rate = 50 MS/s * 16 (short) = 800 Mbits/s ==> < Gb/s.
We don't have an interp by 2 mode yet, but it could be done. However, as I stated above, I don't think you need it to do what you want to do.
Matt
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