Three different USRP2 nodes are transmitting with almost exactly 1 MHz frequency offset

GNU Radio
1

Hello,

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.

Thanks,

Nazmul

–
Muhammad Nazmul I.

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

2

On Wed, Feb 08, 2012 at 06:39:24PM -0500, Nazmul I. wrote:

./benchmark_tx.py -f 2.4G -r 1M -m gmsk -M 10 -a “addr = 192.168.10.2”
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?
(uhd_usrp_probe --version)

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

Jason

3

Thanks for the reply, Jason. The uhd_usrp_probe --version command gave
the
following result:

linux; GNU C++ version 4.4.5; Boost_104200; UHD_003.004.000-71810ad

003.004.000-71810ad

Do I have to download the latest UHD image? The image that I am using
right
now was downloaded by one of my colleagues and I think that he did it
recently.

Also, I tried running the benchmark_tx and benchmark_rx codes with a 1
MHz
frequency offset input, i.e., I gave the following commands:

./benchmark_tx.py -f 2.4G -r 1M -m gmsk -a “addr = 192.168.10.2”

./benchmark_tx.py -f 2.401G -r 1M -m gmsk -a “addr = 192.168.10.2”

Since the uhd_fft.py and the my lab spectrum analyzer show a 1 MHz
frequency offset, I assumed that the above commands would work.
Unfortunately, this did not help either!

Suggestions will be very appreciated.

Thanks,

Nazmul

On Wed, Feb 8, 2012 at 7:37 PM, Jason A. [email protected] wrote:

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

Jason

–
Muhammad Nazmul I.

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

4

Hello Ben,

Shantharam, my colleague, installed the latest UHD image. Now I don’t
see
the 1 MHz frequency offset any more. The benchmark_rx program is also
receiving packets correctly from the benchmark_tx code.

Thanks a lot for your help. We really appreciate your effort.

Nazmul

On Thu, Feb 9, 2012 at 12:44 PM, Ben H. [email protected] wrote:

$ git checkout master
On Wed, Feb 8, 2012 at 8:52 PM, Nazmul I. [email protected]wrote:

recently.
Unfortunately, this did not help either!
On Wed, Feb 8, 2012 at 7:37 PM, Jason A. [email protected] wrote:

them are transmitting with 1 MHz frequency offset! I have attached two

exactly

Wireless Information & Networking Laboratory
Rutgers, USA.

Discuss-gnuradio mailing list
[email protected]
Discuss-gnuradio Info Page

–
Muhammad Nazmul I.

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

5

Nazmul -

Your version of UHD is from November 22nd. Will you try updating your
UHD
install?

I’m not sure how you installed, or how familiar you are with git / Linux

here is a quick command list, assuming you used Git to checkout the code
to
begin with, and it is in a directory called uhd.git/

$ cd uhd.git
$ git checkout master
$ git remote update; git pull
$ rm -rf build
$ mkdir build; cd build
$ cmake …/ && make

Let us know how it goes!

Cheers,
Ben

6

Hi Ben,

I am happy to hear from Nazmul that the image works.

Thanks a lot for your help.

Have a nice weekend

7

Hi all -

I’m glad the update fixed it for you!

Cheers,
Ben

On Sat, Feb 11, 2012 at 3:56 PM, shantharam balasubramanian <