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.
For use with the rtl_tcp utility acting as a spectrum server.
The "empty" rtl_tcp= device hint might be used to connect to rtl_tcp
running on local machine.