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Re: [Discuss-gnuradio] benchmark_xx.py Transmits Images at +/- 0.5MHz Wh

From: Josh Blum
Subject: Re: [Discuss-gnuradio] benchmark_xx.py Transmits Images at +/- 0.5MHz When Center Freq Is 2.4GHz [USRP N200 and XCVR2450]
Date: Wed, 02 May 2012 21:14:13 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120410 Thunderbird/11.0.1

On 05/02/2012 07:42 PM, jasonatran wrote:
> Hi All,
> I have a pair of USRP N200s with XCVR2450 daughterboards running the latest
> GNU Radio version with UHD. This is an odd problem, but I'm wondering if
> anyone has seen this before.
> When I run the benchmark_rx.py/benchmark_tx.py specified at 2.4GHz, the
> transmitter is transmitting images of lower magnitude at +/- 0.5MHz, and the
> receiver isn't able to decode any radio packets. Some frames are received,
> but they are all "ok=FALSE" with the lengths lower than the length of the
> actual packet sent. These images persist when I set the XCVR2450's to tx/rx
> within its specified frequency range. 

Do you have a screencap of the problem spectrum? Maybe from the
perspective of the receiver.

> note: the benchmark scripts are from
> ~/gnuradio/gr-digital/examples/narrowband/
> However, when I run the benchmark scripts at "--freq 0" on both sides, the
> transmitter says it is automatically set to "4800MHz" (although this is
> outside of the XCVR2450's range), and the receiver says it is automatically
> set to "2400MHz." Somehow, the transmitter is transmitting at 2.4GHz and the
> receiver is tuned to 2.4GHz. The signal is clean, and there are no images in
> sight. I used both uhd_fft.py and a spectrum analyzer to check.

Well XCVR2450 has a dual band. I think you are seeing some weirdness
with the code either trying to auto select the middle frequency, and the
actual frequency being coerced.


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