Re: [Discuss-gnuradio] [USRP-users] Getting a -135 dBm/Hz noise spectral
From:
Nazmul Islam
Subject:
Re: [Discuss-gnuradio] [USRP-users] Getting a -135 dBm/Hz noise spectral density in USRP N210
Date:
Wed, 27 Jun 2012 11:17:44 -0400
You are exactly right! We were using TX/RX antenna port in the WBX receiver daughterboard. I get almost -170 dBm/Hz noise spectral density when I select RX2. This is almost perfect!
Thanks! Your email increased my pathloss calculation range by 30 dB :)
Nazmul
On Wed, Jun 27, 2012 at 9:22 AM, Jason Roehm <address@hidden> wrote:
Do you have the correct antenna port selected? I believe that RX2 is
the default for the SBX. If you are injecting signal into the port
that isn't selected, then you'll see ~30-40 dB of isolation in the
front-end antenna switch. That seems to be in the neighborhood of
the difference that you're seeing.
Jason
On 06/27/2012 01:51 AM, Nazmul Islam wrote:
Hello,
I am trying to measure channel path loss using two USRP N210. I
need to measure the noise floor so that I can find the threshold
for pathloss measurement. I am using the attached flowgraph to
calibrate the receiver signal strength. I tried two ways to
calibrate the receiver power and both show me approximately -135
dBm/Hz noise spectral density.
1. At first I don't transmit anything and measure the power of the
floating point numbers that is coming out of rx USRP block. Then
I transmit a PN sequence of -5 dBm power at 17 MS/s from an USRP.
I connect this USRP through a 60 dB attenuator to the receiver
USRP. This input (-65 dBm) seems to double the power of the
floating point numbers. I infer that the my USRP noise floor is
equivalent to -65 dB at 17 MHz.
2. I also apply an external 1 MHz noise source of -75 dBm power to
the receiver USRP. This leads to an increase of 3 dB power in the
receiver FFT plot. This also suggests I have -75 dBm noise power
at 1 MHz.
Both these experiments suggest -135 dBm/Hz noise spectral density
in my rx USRP. However, this is very far from theoretical noise
spectral density (approximately -170 dBm/Hz). My Rx USRP N210 has
a WBX daughterboard and my Tx USRP has an SBX daughterboard. The
ettus websites suggest only 6 dB noise figure (http://code.ettus.com/redmine/ettus/documents/16).
If my USRP daughterboard is not faulty, I must be giving some
wrong parameters. I put the RX gain as 30 dB to get the full range
of WBX daughterboards (http://files.ettus.com/uhd_docs/manual/html/dboards.html).
Shall I increase it more?
Thanks for your help.
Nazmul
--
Muhammad Nazmul Islam
Graduate Student
Electrical & Computer Engineering
Wireless Information & Networking Laboratory
Rutgers, USA.