[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] Re: uses gr.file_sink 32 bit or 64 bit

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Re: uses gr.file_sink 32 bit or 64 bit
Date: Fri, 27 Mar 2009 09:16:32 -0700

Just to make this completely clear:

The complex baseband samples that come from the USRP1 source block
usrp.source_c(), and the from USRP2 source block usrp2.source_32fc(),
are complex numbers.  The real portion of the sample (the "in-phase",
or "I" portion), is a 32-bit floating point number.  The imaginary
portion of the sample ("quadrature", or "Q" portion) is also a 32-bit
floating point number.

The sample, then, is a vector quantity.  While there is a "total" of
64 bits between the two numbers, when one uses bit depth to describe
these, one still refers to the bit depth of the individual dimensions,
not the aggregate.  To describe the storage requirements of a sample,
in memory or on a block device, one typically uses bytes.  Thus, it is
correct to say, "a 32-bit complex floating point sample takes 8 bytes
of storage, 4 for the I portion and 4 for the Q portion."

Your earlier post showing the captured samples from the USRP as an
array in Octave was correct.  (The magnitude spike in the first 20 or
so samples is an artifact of the the USRP when it is first enabled,
and can be ignored.)

Hope this helps.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]