# Tx-power usrp n210 and wbx doughterboard

**URL:** <https://www.ruby-forum.com/t/tx-power-usrp-n210-and-wbx-doughterboard/231116>\
**Category:** GNU Radio\
**Created:** [July 22, 2014, 10:15am UTC](https://www.ruby-forum.com/t/tx-power-usrp-n210-and-wbx-doughterboard/231116 "2014-07-22T10:15:11Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [July 22, 2014, 10:15am UTC](https://www.ruby-forum.com/t/tx-power-usrp-n210-and-wbx-doughterboard/231116/1 "2014-07-22T10:15:11Z")

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Hi at all,

I have problem to understand how an USRP used as a trasmitter works in  
term  
of transmitted power when we fix a tx\_gain.

Let me explain better:

- The WBX Daughterboard is a wide bandwidth transceiver that provides up  
to  
100 mW of output power and a noise figure of 5 dB. (extracted from  
manual)
- UHD USRP SINK block (in gnuradio) allows to set the tx\_gain(dB)

Which is the relation between these parameters???  
If I want to set a specific transmitted power???

Thanks in advance,

* * *

Ing. Simone Ciccia, PhD Student  
Antenna and EMC Lab (LACE),  
Politecnico di Torino,  
C.so Duca degli Abruzzi 24, 10129 Torino, Italy

removed\_email\_address@domain.invalid

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**Author:** ![Simone\_Ciccia\_S2106](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e495f1/32.png) [@Simone\_Ciccia\_S2106](https://www.ruby-forum.com/u/Simone_Ciccia_S2106)\
**Post date:** [July 22, 2014, 10:47am UTC](https://www.ruby-forum.com/t/tx-power-usrp-n210-and-wbx-doughterboard/231116/2 "2014-07-22T10:47:07Z")

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Simone,

the actual tx power depends on a lot of parameters, and it is not a  
simple setting. For one thing, it depends a lot on the actual signal you  
are generating. If you need a very specific output power, you need to  
calibrate your setup with a tool such as a spectrum analyzer.

In general, the 100 mW (or 20 dBm) is the max possible tx power. The  
gain will reduce that. Obviously, the noise figure is not relevant for  
Tx.

M

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**Author:** ![Simone\_Ciccia\_S2106](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e495f1/32.png) [@Simone\_Ciccia\_S2106](https://www.ruby-forum.com/u/Simone_Ciccia_S2106)\
**Post date:** [July 22, 2014, 4:09pm UTC](https://www.ruby-forum.com/t/tx-power-usrp-n210-and-wbx-doughterboard/231116/3 "2014-07-22T16:09:22Z")

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As Martin said, it really helps to have a spectrum analyzer. What I’ll  
do is  
generate a CW tone (sinusoid) of 0.707 Vp; that is 3 dB backed off from  
DAC  
full scale power. Then I’ll increase the TX gain setting until the TX  
image  
rejection starts to become poor. This will typically be 15 dBm for low  
frequencies (\< 500 MHz), and will increase with frequency. These  
settings  
would be the maximum you want to transmit. If linearity is a concern,  
you’ll want to do the same but generate two tones at 0.35 Vp and look at  
the  
intermod levels, then back off TX gain to maybe -30 dBc intermod.

Once you have that max level set, it really depends on the statistics of  
you  
signal; peak-average ratio or CCDF (see link). If you stay 3 dB backed  
off  
from both DAC full scale and TX chain P1dB, you should be OK for most  
signals unless you are doing OFDM or other multi-carrier stuff.

[http://www.emce.tuwien.ac.at/hfadmin/354059/download/Characterizing\_Digitally\_Modulated\_Signals\_width\_CCDF\_Curves\_\_Agilent\_Application\_Note\_5968-6875E\_.pdf](http://www.emce.tuwien.ac.at/hfadmin/354059/download/Characterizing_Digitally_Modulated_Signals_width_CCDF_Curves__Agilent_Application_Note_5968-6875E_.pdf)

Lou  
KD4HSO

Simone Ciccia S210664 wrote

> - UHD USRP SINK block (in gnuradio) allows to set the tx\_gain(dB)
> 
> Which is the relation between these parameters???  
> If I want to set a specific transmitted power???

–  
View this message in context:  
[http://gnuradio.4.n7.nabble.com/TX-POWER-USRP-N210-AND-WBX-DOUGHTERBOARD-tp49481p49489.html](http://gnuradio.4.n7.nabble.com/TX-POWER-USRP-N210-AND-WBX-DOUGHTERBOARD-tp49481p49489.html)  
Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).

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**Author:** ![Simone\_Ciccia\_S2106](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e495f1/32.png) [@Simone\_Ciccia\_S2106](https://www.ruby-forum.com/u/Simone_Ciccia_S2106)\
**Post date:** [July 22, 2014, 4:26pm UTC](https://www.ruby-forum.com/t/tx-power-usrp-n210-and-wbx-doughterboard/231116/4 "2014-07-22T16:26:04Z")

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I should note that want I really want to do is automate this measurement  
and  
generate a series of curves that show TX\_gain setting vs. intermod, for  
several frequencies, at -3 dB from full scale. The state of GPIB  
support  
under Linux doesn’t seem to be that great though.

I suppose though that you can loop-back the TX to RX via attenuator, and  
offset tune the RX. This assume the RX linearity is much better than  
TX.

Lou  
KD4HSO

–  
View this message in context:  
[http://gnuradio.4.n7.nabble.com/TX-POWER-USRP-N210-AND-WBX-DOUGHTERBOARD-tp49481p49490.html](http://gnuradio.4.n7.nabble.com/TX-POWER-USRP-N210-AND-WBX-DOUGHTERBOARD-tp49481p49490.html)  
Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).