Issues with rtl_tcp

Leif Asbrink leif at sm5bsz.com
Wed Sep 26 19:33:43 UTC 2012


Hi All,

The GNU licencing of rtl-sdr is the GNU GENERAL PUBLIC LICENSE.

There is also the GNU LIBRARY GENERAL PUBLIC LICENSE that 
better specifies some of the concepts used by the Free 
Software Foundation, Inc.

The library license states that one can change from it to
the general license but that one then not can change back:

"Once this change is made in a given copy, it is irreversible 
for that copy, so the ordinary GNU General Public License 
applies to all subsequent copies and derivative works made 
from that copy."

I am not a lawyer, but it seems to me that this statement
implicates that the library license is more restricted and
that things you are allowed to do under the library license
are still allowed under the general license.

In the library license we can read this:
"5. A program that contains no derivative of any portion 
of the Library, but is designed to work with the Library 
by being compiled or linked with it, is called a "work 
that uses the Library".  Such a work, in isolation, is 
not a derivative work of the Library, and therefore falls 
outside the scope of this License."

This means you are free to use the rtlsdr dll available
at osmocom but you can not distribute an executable in
which the library is linked in.

Likewise can I distribute Linrad under Linux and give
the user the instructions how to link in librtl.so 
from the osmocom site or from a complete and somewhat
modified version that I will supply myself in case
the modifications to the library I will propose will not
be accepted. The e4k tuner works very well, actually it is 
very competitive when compared to the FUNcube Pro dongle, 
but only with a modified library.
http://www.sm5bsz.com/linuxdsp/hware/funcube/funcube.htm

At the moment I am working with the FC0013 code. So far I 
found these things:

The original code uses AGC. To disable it I change the
init for registers 0x0cc and 0x0d:

[0x0c]=0x78 (normal) or 0xb8 (-35 dB gain)
[0x0d]=0x81 (normal) or 0x89 (-60 dB gain)    

Regards 

Leif  /  SM5BSZ

PS. The reason I worry about the GNU license is that 
Linrad is free software. Free for anyone to use for
any purpose. I do not want to discourage people from
using my sdr algorithms in commercial products. For that
reason I claim no copyright and do not include a GNU
license. DS.




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