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[Discuss-gnuradio] Three different USRP2 nodes are transmitting with alm

From: Nazmul Islam
Subject: [Discuss-gnuradio] Three different USRP2 nodes are transmitting with almost exactly 1 MHz frequency offset
Date: Wed, 8 Feb 2012 18:39:24 -0500


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 ="

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.



Muhammad Nazmul Islam

Graduate Student
Electrical & Computer Engineering
Wireless Information & Networking Laboratory
Rutgers, USA.

Attachment: Cropped_node_20_1_tx_shift.png
Description: PNG image

Attachment: Cropped_node1_1_shift.png
Description: PNG image

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