[USRP-users] b210 tx power

Marcus Müller marcus.mueller at ettus.com
Thu Oct 30 07:02:36 EDT 2014


Hi Ralph, Hi Dmitry,

I don't have measurements for the b210, but the ones for the b200 tx
(which should be pretty identical to the b210) indicate that the
variation of TX power between 100MHz and 2GHz is about 6dB max (for the
30dB gain case). So, depending on what you consider to be remarkable,
you might call this a remarkable drop; however, I don't think TX power
is that critical for GSM; what are the operational differences you see
at 1.8GHz?

Regarding Dmitry's Measurements:

DBPSK might not be the measurement tool of choice, here, as sending
modulated data with (I'm assuming two samples per symbol, no further
filtering), 250k symbols/s cannot work well if your analyzer measures
the energy per frequency spot for only 20µs at best.
As Ralph said, you should go for something easier to recognize sprectrally.
UHD comes with a handy example, tx_waveforms, which you can use like:

tx_waveforms --rate 0.5e6 --gain 75 --wave-type SINE --wave-freq 1e3
--freq 433e6

If you're already using GNU Radio, you could also generate noise (using
the noise source) and feed that directly into your USRP sink, and that
should give you something broad.

Another thing that happened to me a few times and made me question my
sanity was connecting to the wrong port of my USRP (that was with N210s,
though).

Greetings,
Marcus

On 30.10.2014 08:19, Ralph A. Schmid, dk5ras via USRP-users wrote:
> First of all you need to know that  your signal occupies a large bandwidth,
> so the energy is spread and does not reach the 20dBm line on your analyzer.
> To see the real peak power the easiest way is to transmit an unmodulated
> carrier and watch this with the analyzer. 
>
> Then of course the PA does not have identical gain over the whole frequency
> range, you can get an idea by having a look at the data sheet of the MMIC.
> So it will drop with higher frequency. Without having measured it, I expect
> a remarkable drop when going above 1 GHz. My quick comparison with OpenBTS
> using 900 and 1800 MHz for GSM transmissions seems to prove this.
>
> Ralph.
>
>> -----Original Message-----
>> From: USRP-users [mailto:usrp-users-bounces at lists.ettus.com] On Behalf Of
>> Dmitry via USRP-users
>> Sent: Thursday, October 30, 2014 7:27 AM
>> To: usrp-users at lists.ettus.com
>> Subject: [USRP-users] b210 tx power
>>
>> 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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