Interpolator half band FIR filter optimization
The process has been optimized by using only the non null samples for calculation. This closes ticket #24
This is explained here: https://dspguru.com/dsp/faqs/multirate/interpolation/
And graphically here: http://home.etf.rs/~milic/Solution_Manual/Chapter_7_exercises/fig_07_06.gif
This results in a significant improvement for all sink plugins when the software interpolator is engaged. This concerns BladeRF, HackRF and LimeSDR output plugins. In addition all output channel plugins also benefit from it for their half-band interpolation chain (excludes the rational interpolator).
HackRF plugins start/stop fix
Rationalize the start/stop sequences of the HackRF input and output plugins. This also uses the latest version of libhackrf (commit 9bbbbbf) that fixes the start and stop rx/tx streams bug. You will need to upgrade your HackRF to the 17.02.1 firmware.
WFM demodulator improvements
- added a signal gauge
- added an audio mute button with green lighting when squelch is open
- fixed excursion handling and use the atan2 approximation for the discriminator
Other changes
- CW Keyer: specifiy char signedness to fix error with some compilers
- LimeSDR input and output plugins are available in the .deb package for ARM