rtl dongle output a 8bit unsigned interger for both I/Q signals.
To convert it to float man must remove the zero value.
A signed 8bit is normally between -128 and 127 so the convertion must
be something like :
I=(float)rtlinbuff[i++]-128.0; /* with rtlinbuff the input 8bit
unsigned buffer */
Q=(float)rtlinbuff[i++]-128.0; /* and I/Q float values */
But, I try to find that 0 level by a very simple low pass filter.
something like :
IM=0.99999*IM+0.00001*(double)rtlinbuff[i++];
QM=0.99999*QM+0.00001*(double)rtlinbuff[i++];
and after a few seconds of running with antenna disconnected , I find a
value around 127.35 for a first dongle and 127.4 for a second.
I do some differents runs and these values seem consistant.
So,
1) is it something true with other dongles ?
2) Is it documented somewhere and I just discover what everybody knows ?
3) It will be interesting to modify rtl_test to show this value if it
vary from one dongle to another.
