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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2
From: |
Marcus D. Leech |
Subject: |
Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2 |
Date: |
Wed, 17 Nov 2010 02:33:05 -0500 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 |
On 11/17/2010 02:20 AM, Matt Ettus wrote:
>
>
> Decimation is filtering. When you decimate by 512 you are reducing
> noise by a factor of 512 (27dB). Since you are using a BasicRX, there
> will be very little noise, and 27dB less after decimation. In fact,
> there is so little noise that the output of the filters is a constant
> 0 once it is rounded to 16 bit ints. That is why the FFT results
> essentially show negative infinity.
>
Well, OK, I'll buy that. But there's a significant change below
decimation=256. A non-linear
jump from "reasonable-looking data" to "negative infinity".
I'm seeing a jump from a level of around -20dB to "negative infinity" by
changing decimation from
256 to 260, which is a noise bandwidth change of something like 0.04dB.
So while I'm totally willing to believe that a gross change from 400KHz
to 200KHz might cause a
bit of weirdness, it seems highly counter-intuitive that a small
change as implied by
decimation=256 to decimation=260 would cause a huge nonlinear leap in
filter output in
the decimator.
--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
- [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/14
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/16
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Tom Rondeau, 2010/11/16
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/16
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Tom Rondeau, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Matt Ettus, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2,
Marcus D. Leech <=
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Steven Clark, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Marcus D. Leech, 2010/11/17
- Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2, Tom Rondeau, 2010/11/17