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Re: [Discuss-gnuradio] Three different USRP2 nodes are transmitting with
Re: [Discuss-gnuradio] Three different USRP2 nodes are transmitting with almost exactly 1 MHz frequency offset
Wed, 8 Feb 2012 16:37:47 -0800
On Wed, Feb 08, 2012 at 06:39:24PM -0500, Nazmul Islam wrote:
> I am running the benchmark_tx.py codes and looking at the spectrum of the
> signals using uhd_fft.py. I am using the latest image of GNU radio
> (GNUradio 3.5) and I have XCVR2450 daughterboards. I ran the
> benchmark_tx.py code in three transmitter nodes and surprisingly, all of
> them are transmitting with 1 MHz frequency offset! I have attached two
> screenshots with the email (I hope that they go through). I give the
> following input parameters to run the benchmark_tx code.
> ./benchmark_tx.py -f 2.4G -r 1M -m gmsk -M 10 -a "addr = 192.168.10.2"
> Both uhd_fft.py and the spectrum analyzer of my laboratory show that the
> received signal is centered at 2.401 GHz. I varied the frequency to 2.45
> GHz, 2.41 GHz, but this 1 MHz frequency shift persists.
> When I run the benchmark_rx.py code at the receiver nodes, they don't
> receive/detect any packets (due to the frequency offset, I guess). I even
> tried to run the transmitter at 2.4 GHz and the receiver at 2.401 GHz.
> However, that did not help either!
> I will try to modify the control loop gain parameters using Tom's blogs
> suggestions and see if that helps. However, I am really surprised to see
> how all three different transmitter nodes can transmit with almost exactly
> 1 MHz frequency offset. Any suggestion will be appreciated.
Can you tell us which version of UHD you are using?
We have heard reports of such an issue and my best guess is that it was
related to an accidental swap of I and Q in the XCVR2450 transmitter
code. This went in after the 3.3.2 release and is fixed on latest UHD
master since 837437c65ce36d418cceb3df5b093f9497b3af5f