# Problem setting USRP transmitting signal power

**URL:** <https://www.ruby-forum.com/t/problem-setting-usrp-transmitting-signal-power/226896>\
**Category:** GNU Radio\
**Created:** [February 25, 2013, 4:38am UTC](https://www.ruby-forum.com/t/problem-setting-usrp-transmitting-signal-power/226896 "2013-02-25T04:38:01Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![warren4300137](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3e96dc/32.png) [@warren4300137](https://www.ruby-forum.com/u/warren4300137)\
**Post date:** [February 25, 2013, 4:38am UTC](https://www.ruby-forum.com/t/problem-setting-usrp-transmitting-signal-power/226896/1 "2013-02-25T04:38:01Z")

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Hi~

I found some strange problem setting USRP transmitting signal power. The  
method I change the transmit power is to use a constant to multiply the  
signals. the problem is that I use bigger constant like 2.0, the SNR  
value i  
calculate is lower than using constant like 1.0. the transmit signal  
values  
are 0.005,-0.005. my experiment platform is USRP N210 plus motherboard  
RFX2400. Is there anything wrong or there are better method to setting  
USRP  
transmiting power?

thanks!!!

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**Author:** ![warren4300137](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3e96dc/32.png) [@warren4300137](https://www.ruby-forum.com/u/warren4300137)\
**Post date:** [February 25, 2013, 3:48pm UTC](https://www.ruby-forum.com/t/problem-setting-usrp-transmitting-signal-power/226896/2 "2013-02-25T15:48:13Z")

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On Sun, Feb 24, 2013 at 10:36 PM, warren4300137  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> thanks!!!  
> The USRPs take in normalized signals, so you want to scale your  
> signals to +/-1 at most. If you want increased power, adjust the gain  
> of the USRP itself.

The reason you’re seeing a bad signal as you increase the amplitude is  
that you are causing nonlinearities in the hardware from a signal  
that’s too large. So even though the USRP will take in a +1 signal,  
you’ll want to back off some to keep the signal in the linear range of  
the transmitter.

Tom

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<div class="post-metadata">

**Author:** ![warren4300137](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3e96dc/32.png) [@warren4300137](https://www.ruby-forum.com/u/warren4300137)\
**Post date:** [July 4, 2013, 1:49pm UTC](https://www.ruby-forum.com/t/problem-setting-usrp-transmitting-signal-power/226896/3 "2013-07-04T13:49:44Z")

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Hi,

> that’s too large. So even though the USRP will take in a +1 signal,  
> you’ll want to back off some to keep the signal in the linear range of  
> the transmitter.
> 
> Tom

So how much should one want to back off? Can u please quantize the  
complex sample amplitudes that would map to the linear region of the  
transmitter? I am using USRPN210 with XCVR2450. Thanks.