[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] log POWER FFT Output - Samples flipped in frequen

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] log POWER FFT Output - Samples flipped in frequency
Date: Mon, 19 Jan 2015 08:46:22 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16

On 01/19/2015 07:24 AM, Jorge Gallo wrote:

I am working with a B200 and GNURadio over Debian. At first sight, UHD driver and GNURadio work fine with my B200.

In my first example I am sampling at 2Msamples centered at 938MHz. I generate a 20KHz FM signal with my generator at 937.1MHz.

When doing an FFT I see clearly my signal at the expected level/freq. However I want to estimate power (I am aware that I need calibration in order to give an accurate power figure).

I set in GRC an USRP signal source followed by an "log POWER FFT" (1024 points) and a sink file.

Furthermore I see those samples in real time with a "QT GUI Vector sink" and I realized that the samples from "log POWER FFT" are flipped. I mean the first samples I get are from 938 to 939MHz and then from 937 from 938MHz.

Does it make sense? ( I expected to get them from 937 to 939MHz without any jump). (The same way as using a FFT sink).

The aim of my example is to monitor the presence of power at certain bands.

Thanks in advance,


_______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
That's normal for FFTW-based FFTs (and a lot of others).

The output goes from:

DC to BW/2
-BW/2 to DC

Where BW is your signal bandwidth.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

reply via email to

[Prev in Thread] Current Thread [Next in Thread]