Forum: GNU Radio I couldn't observe 2.4G Wi-Fi signal and didn't know why

47f3f4f78bd096f32f5b1d17179634d0?d=identicon&s=25 Howard He (Guest)
on 2013-11-10 04:55
(Received via mailing list)
I know this may due to stupid reasons while I have no idea how to
achieve it.


Ubuntu 13.04(32-bit); gnuradio-3.6.5; GNU C++ version 4.7.3;
Boost_105300; UHD_003.005.004-154-ge6a1de6d; USRP N210; RFX2400

There are two Wi-Fi APs in our lab with 802.11g and 802.11n standard. I
use a simple software "wavemon" to get their information about channel
and signal strength.

I use four antennas for test. Two are official VERT2400, others are 2.4G
antennas. I use the given example "uhd_fft.grc" (a simple FFT block)
hoping to observe frequency spectrum of Wi-Fi signal. No matter what
antenna I set up (even without antenna) and what central frequency I
tune,  the FFT window only shows something like noise around -50--60dB
on whole spectrum (sample rate=25M) which is unlike the 802.11 standard.

There is low possibility of bad hardware I guess. I doubt that there may
be some problems with my test methods and hope for some advice.

Thanks!
Ad80d352eb445a3d7dccd5a779db0e43?d=identicon&s=25 Martin Braun (CEL) (Guest)
on 2013-11-10 18:05
(Received via mailing list)
On Sun, Nov 10, 2013 at 11:53:41AM +0800, Howard He wrote:
> I use four antennas for test. Two are official VERT2400, others are 2.4G
> antennas. I use the given example "uhd_fft.grc" (a simple FFT block) hoping to
> observe frequency spectrum of Wi-Fi signal. No matter what antenna I set up
> (even without antenna) and what central frequency I tune,  the FFT window only
> shows something like noise around -50--60dB on whole spectrum (sample rate=25M)
> which is unlike the 802.11 standard.
>
> There is low possibility of bad hardware I guess. I doubt that there may be
> some problems with my test methods and hope for some advice.

Hi Howard,

have you made sure the wifi stations are actually transmitting? Do you
have a real spectrum analyzer which shows energy transmitted?
And are you on the correct centre frequency?

MB

--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstra├če 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-W├╝rttemberg and
National Laboratory of the Helmholtz Association
C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2013-11-10 18:35
(Received via mailing list)
On Sun, Nov 10, 2013 at 12:03 PM, Martin Braun (CEL)
<martin.braun@kit.edu> wrote:
>
> Hi Howard,
>
> have you made sure the wifi stations are actually transmitting? Do you
> have a real spectrum analyzer which shows energy transmitted?
> And are you on the correct centre frequency?
>
> MB

Also remember that Wifi is bursty and can be fairly low power. You
won't see it constantly and will only see bursts of energy. If you do
a peak/max hold you'll start seeing something and a
spectrogram/waterfall plot will show you the the signal bursts.

Tom
7d89a70df32c0ae27c1235016f9e5441?d=identicon&s=25 marcus (Guest)
on 2013-11-11 12:49
(Received via mailing list)
Hi Howard,

as for things that can cost you a lot of time to figure out, until you
start all over again with calibration:

Have you made sure that you attach the antenna to the correct RF port
of the USRP, and connect that port to the correct connector on the
daughterboard?

Greetings,
Marcus
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