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Re: [Discuss-gnuradio] Different amplitude on two USRPs

From: Jamie Wo
Subject: Re: [Discuss-gnuradio] Different amplitude on two USRPs
Date: Tue, 22 May 2012 23:56:45 +1000

Hi Marcus,

Thanks for your reply.  However, I already set the gain to 30 on the two USRPs.  I mean the pictures I attached before is based on the same gain setting. Is there any other method to control this? The big difference in amplitude looks really strange. Should be a way to solve this.



On Tue, May 22, 2012 at 11:46 PM, <address@hidden> wrote:

One of the controllable parameters of a USRP source/sink is gain. 

If you're using rx_samples_to_file, then yes the "--gain" argument is the one you want--this controls the analog RF gain of the board.




On Tue, 22 May 2012 23:42:40 +1000, Jamie Wo wrote:

Hi Marcus,

Thanks. The daughter boards I am using are WBXs.

I can understand how to use multiply-const block to change the amplitude of the received signal, but what does the first method mean?

Does it mean to set the parameter in help message "- - gain arg       gain for the RF chain"  or on hardware level? I did not see any button on motherboard or daughterboard for adjusting RF gain.



On Tue, May 22, 2012 at 11:27 PM, <address@hidden> wrote:

You don't say what daughtercards you're using --many of them allow you to set the RF (analog) gain on the card.

YOu can also modify the magnitudes of the signals using a multiply-const block in Gnu Radio.




On Tue, 22 May 2012 23:23:49 +1000, Jamie Wo wrote:

Thanks for your reply.

I understand the received signals on two USRPs are not likely to be exactly the same. I wonder is there a way to adjust either USRP or modify software setting in gnuradio to make the amplitude close?

Actually, what I got from two USRPN210s has a big difference in amplitude, as shown in the attachment. How can I handle this?



On Tue, May 22, 2012 at 10:56 PM, <address@hidden> wrote:

On Tue, 22 May 2012 22:40:11 +1000, Jamie Wo wrote:

Hi all,
I met a werid problem when receiving. When I ran 'rx_samples_to_file' example to receive signal from a signal source, e.g. radio station, on two USRPN210s, the amplitude of received signals are different, seen from gnuplot. 
Does anyone know why this happenes? I guess this is the problem of USRP, because I ran the same program, set the same parameters for 'rx_samples_to_file', receive the same signal source and the two USRP N210s were placed next to each other on the table. 
Is there a way to set USRP/daughterboard so that the received signals have the same amplitude on two USRPs or adjust other parameters in gnuradio/uhd to do that? 

Analog electronics can have variability in gain response, perhaps as much as 2dB for nominally-identical daughter-cards, and identical gain settings.

Furthermore, propagation can often lead to variations in signal strength between two identical receivers, with identical antennae even in the same physical area, especially in the presence of multi-path signal propagation.


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