This commit adds the function rtlsdr_set_direct_sampling()
which can be used to enable/disable a mode where the
RTL2832 acts as a direct sampling receiver.
This mode disables the tuner, and by attaching a long
wire, or better, a 50Ω to 200Ω transformer and a lowpass-
filter to the In-phase ADC input (pin 1 or 2 of the RTL2832,
whereas pin 1 is at the molded dot) it is possible to listen to
shortwave radio stations. The coupling capacitors can be
left in place, but for better results they should be removed.
Tuning in this mode is done with the DDC, and since the
ADC samples with 28.8 MHz, tuning is possible from 0 to
28.8 MHz.
Signed-off-by: Steve Markgraf <steve@steve-m.de>
