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[Discuss-gnuradio] File format question

From: Bahn William L Civ USAFA/DFCS
Subject: [Discuss-gnuradio] File format question
Date: Tue, 14 Aug 2007 14:57:46 -0600

I have a few questions, but they mostly come down to: What is the data file 
format when using a file as a signal source?

>From http://www.nd.edu/~jnl/sdr/docs/tutorials/9.html#tth_sEc3.3

2.5  File sources
Block: gr.file_source
gr.file_source ( size_t         itemsize,
                 const char *   filename,
                 bool           repeat )

Notes: gr.file_source reads the data stream from a file. The name of the file 
is specified by filename. The first argument itemsize determines the data type 
of the stream, such as gr_complex, float, unsigned char. The argument repeat 
decides whether the data in the file is sent repeatedly. As an example, we can 
use the block in this way in Python:
src = gr.file_source (gr.sizeof_char, "/home/dshen/payload.dat", TRUE) 

Question #1: What is the syntax for the itemsize argument?

Since the example doesn't use one of the data types mentioned, it is hard to 
tell what the syntax is supposed to be. For instance, if I want to use 
gr_complex, do I specify gr.sizeof_gr_complex? If I want to use unsigned char, 
is it "gr_sizeof_unsigned_char" so as to eliminate the space?

Question #2: What are all of the options for the itemsize argument?

It lists "gr_complex", "float", and "unsigned char" yet the example uses one 
that is not in the list. Are there others?

Question #3: Does the data file format for transmitting match the data file 
format when receiving?

Can I take a file that is recorded, say using receive_file_c.py (may not have 
the file name exactly correct) and use that as a source without modification? 
If so, what does it mean to use IQ pairs as input data? What does the USRP do 
with them?

If I use a data size of "gr_sizeof_float" does that mean that my data file 
should consist of a list of floating point values stored as IEEE single 
precision values where each value represents a time-sampled baseband data point?


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