[USRP-users] USRP transmission power

Marcus Müller marcus.mueller at ettus.com
Thu Apr 30 08:40:27 EDT 2015


Hello Alok,

> Would you please comment that how can i get the transmission power at
> the above mentioned setup.  
use a calibrated measurement device -- as I explained, there's nothing
else you can do.
> However, i am able to get the avg received power per sample at
> receiver. say for eg. 8.8836e-06.
No! What you get are digital samples, which are,  proportional to the
voltage that the ADC saw. That voltage in turn might be proportional, in
the best case (which you're free to assume in most of the operating
range of the USRP), to the voltage seen at the antenna port, but that's
just a "proportional to" relationship, and by no means the power itself.
>  SO can I simply square the avg received power 
you're mixing things up. You receive samples having a magnitude that is
proportional to voltages at the ADC. If you square that magnitude, you
get something that is proportional to the square of these voltages, and
hence proportional to the power of the signal.
> to get the transmitted power at that particular frequency and gain??
No. You need to use a measurement device that is calibrated to calibrate
your system.

Best regards,
Marcus

On 04/30/2015 12:25 PM, alok ranjan via USRP-users wrote:
> Hello Marcus,
>
> Thank you for your prompt reply on the mentioned question.  Since, I
> am new to the USRP community so I need some more expert suggestion
> from your end. I am just using the benchmark python script i.e.
> benchmark_tx.py and benchmark_rx.py  for sending and receiving. Please
> Find below my complete set up,
>
> Say, benchmark_tx.py -f 500e6 -M 0.5 --tx -gain=30  --tx-amplitude=0.8
> -m qam
>
> using the same for benchmark_rx.py also.
>
> Would you please comment that how can i get the transmission power at
> the above mentioned setup. 
>
> However, i am able to get the avg received power per sample at
> receiver. say for eg. 8.8836e-06.
>  SO can I simply square the avg received power to get the transmitted
> power at that particular frequency and gain??
>
>
> Thank you , Best Regards
>
> Alok
>
>
>
>
> ------------------------------------------------------------------------
> Date: Thu, 30 Apr 2015 11:53:45 +0200
> To: usrp-users at lists.ettus.com
> Subject: Re: [USRP-users] USRP transmission power
> From: usrp-users at lists.ettus.com
>
> Hi Alok,
>
>     How can I calculate the transmission power?
>
>
> the power you transmit of course depends primarily on the signal you
> transmit, on the TX gain you set, on your individual antenna, on the
> frequency you're on, and to a certain degree on individual component
> tolerances on the transmitting WBX. The only way of /knowing/ your
> power is measuring in exactly the set up you have.
> However, the USRPs/daughterboards are quite linear over quite a large
> range, so if you take a signal, measure the power, and then use the
> same signal but multiplied with 0.5, you'll get one fourth of the
> energy -- thus, you can generally assume signal energy to be
> proportional to the square of your digital samples' magnitude.
>
>     Another question i have,  can i change the transmission power for
>     every transmission purpose?
>
> Of course. Just change the signal you're transmitting, or change the
> TX gain, or do both.
>
> Best regards,
> Marcus
>
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