Radio and TV uses full spectrum, so they set channels to 0, this will
define a center frequency only. The spectrum is then processed by the
applications and not by libsdr.
The sample rate must be a factor of 1e9, so that time stamps work
and signal has no gaps/glitchs.
If one channel is used, shift the center frequency down by half of the bandwidth.
If more channels are used, select a center frequency between two channels close to the center, but equal distance.
Show the spectum layout on startup.
This patch reverts f1292a985b
LimeSDR mini (and maybe others) do not want IQ data to become a value below
-1 or above 1. This happens slightly when applying the IIR filter after
upsampling. To prevent this, we scale down the IQ level a little bit.
To test the problem:
- set the scale level to 1.0, so it does not take effect
- use LimeSDR mini
- use upsampling (sample rate differs SDR sample rate)
- run loopback mode 2 (-l 2)
- IIR filter must be initialized with 2 or more iterations to take effect
- check linear IQ graph; it will then plot dots inside the circle