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I am currently working with a USRP B200 mini-i to receive 802.11 signals from various usb wifi devices. When sending packets with the USB device over a channel, lets say 2.412GHz, i can't really see pakets that look like a typical OFDM signal (e.g. with the distinctive preamble). What I rather see is some strange looking signals like seen here Gnu Radio window

These signals only show up if I am transmitting with the USB device so it is pretty shure that these signals are coming from the device. Also communication works fine between two usb devices so I assume they are not broken. Does someone know what that is? It is saturating the whole rx-end. I tried different sampling rates (10, 20, 40 and 50 Ms/s) and different frequency channels for transmission and reception. I tested several different usb devices and they all show a similar kind of pattern. My Idea was that this is some kind of bad side emission of the device but its amplitude is pretty high. Just a hint would be awesome !

Cheers Lucas

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  • $\begingroup$ well, clipping happens because the signal is strong at the receiver. does it look normal when you reduce RX gain? $\endgroup$ – Marcus Müller Jan 15 at 13:29
  • $\begingroup$ @MarcusMüller Yes, clipping is not the issue. The saturation diminishes if I reduce gain, increase distance between devices or put my hand inbetween for example. But the waveform by itself looks strange. Or am I missing something? $\endgroup$ – Lucas Jan 15 at 15:06
  • $\begingroup$ hm, for me it's hard to tell whether this is unexpected or expected – for a very regular structured OFDM symbol like a Schmidl&Cox preamble, things don't look like white noise, in time domain. $\endgroup$ – Marcus Müller Jan 15 at 15:18

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