Re: [Discuss-gnuradio] GRC and unit of signal amplitude in USRP

[Martin Braun]

On Thu, Jan 15, 2009 at 03:23:09PM +0100, Bruhtesfa Ebrahim wrote:
> 2. What is the unit of the amplitude that we use in transmitting and
> recieving waveforms in USRP. For instance, in usrp_siggen.py the
> waveform amplitude is set to a default value 16000, so what is this
> number, is this millivolt? Also in usrp_fft.py a reference amplitude
> scale 0f 13490 is used. So, what is the unit of these numbers?

No unit, this is scaling a signal in [-1;1] to +-2^(b-1), where b=16 is
the number of bits we feed or receive from the DAC/ADC. Remember
although most GR blocks use float values, anything talking to the USRP
will eventually have to send integers.
Of course, this relates to volts, but calibrating your hardware to
actually measure an output voltage of your antenna is... difficult to
say the least.

MB

-- 
Dipl.-Ing. Martin Braun           Phone: +49-(0)721-608 3790
Institut fuer Nachrichtentechnik  Fax:   +49-(0)721-608 6071
Universitaet Karlsruhe (TH)       http://www.int.uni-karlsruhe.de/

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