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rtl: remove residue DC component introduced by RTL chip 

received from Juha Vierinen:

A student here noticed that there is dc bias even with the rafael tuner.
We looked into this issue and found that using 127.4f instead of 127.5f
removes this bias. I assume this is associated with a bug in the digital
downconversion of the RTL chip. This change fixes the problem.
This commit is contained in:
Dimitri Stolnikov 2013-07-16 23:31:29 +02:00
parent ffd2bbf424
commit 2d02ae9b83
2 changed files with 5 additions and 5 deletions
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8
lib/rtl/rtl_source_c.cc
View File

@ -170,11 +170,11 @@ rtl_source_c::rtl_source_c (const std::string &args)
// create a lookup table for gr_complex values
for (unsigned int i = 0; i <= 0xffff; i++) {
#ifdef BOOST_LITTLE_ENDIAN
_lut.push_back( gr_complex( (float(i & 0xff) - 127.5f) * (1.0f/128.0f),
(float(i >> 8) - 127.5f) * (1.0f/128.0f) ) );
_lut.push_back( gr_complex( (float(i & 0xff) - 127.4f) * (1.0f/128.0f),
(float(i >> 8) - 127.4f) * (1.0f/128.0f) ) );
#else // BOOST_BIG_ENDIAN
_lut.push_back( gr_complex( (float(i >> 8) - 127.5f) * (1.0f/128.0f),
(float(i & 0xff) - 127.5f) * (1.0f/128.0f) ) );
_lut.push_back( gr_complex( (float(i >> 8) - 127.4f) * (1.0f/128.0f),
(float(i & 0xff) - 127.4f) * (1.0f/128.0f) ) );
#endif
}

2
lib/rtl_tcp/rtl_tcp_source_f.cc
View File

@ -130,7 +130,7 @@ rtl_tcp_source_f::rtl_tcp_source_f(size_t itemsize,
d_temp_buff = new unsigned char[d_payload_size]; // allow it to hold up to payload_size bytes
d_LUT= new float[0xff+1];
for(int i=0; i <=(0xff);++i){
d_LUT[i] = (((float)(i&0xff))-127.5f)*(1.0f/128.0f);
d_LUT[i] = (((float)(i&0xff))-127.4f)*(1.0f/128.0f);
}
// create socket
d_socket = socket(ip_src->ai_family, ip_src->ai_socktype,