[USRP-users] b210 tx power

Stefano Speretta s.speretta at isispace.nl
Thu Oct 30 07:19:26 EDT 2014


Hello Dmitry,
what you see from your analyzer is the power at a particular frequency 
(for example marker 1 is at 432.974 MHz) over a bandwidth equal to your 
resolution bandwidth (18 kHz) and  that value is -8dBm.
But your signal is much wider than 18 kHz (it seems about 360 kHz) so 
you are not measuring the full power transmitted by the radio but only a 
tiny fraction of it.

Please check if your analyzer has a channel power meter option such that 
you can calculate the integral of the power over the full signal 
bandwidth or make your resolution bandwidth wider such that you account 
for all the power transmitted.

 From what I see, I would say that your output power is close to few dBm 
(approximating your signal to have a flat power output over 360 kHz).

Furthermore, what is the absolute accuracy in power of your analyzer? 
Generally it's quite bad on analyzers that do not have a dedicated power 
meter (sometimes up to 1-2 dB).

Regards,
Stefano

On 10/30/2014 07:27, Dmitry via USRP-users wrote:
> Hello!
>
> There were a few topics about b210 TX power. And mentioned value about 50mW. But...We got a very small output power on the different frequencies.
>
> We using an agilent spectrum analizer for power measurement.
> GNUradio DBPSK flowgraph running on the host PC, with gain power control via UHD Sink block, carrier frequency 433MHz, sample rate 500k. On max gain 89dB we see the spectrum with average power -3 dBm.
> B210 and analizer connected via cable with loss about 0.5 dB. Input impedance of analizer 50 Ohm.
> To check the analizer we filed it with  almost the same signal from generator with power 10 dBm and the analizer measured 9.5 dBm (0.5dB loss in cabel).
> The message includes the screenshot in case of Tx_gain=75dB.
>
> Maybe someone spent such measurements and got something like that? What measurement tools u use? What kinds of signal u use? What power value u get?
>
>
> Thanks in advance.
> Dmitry.
>
>
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