The rty decoder for SDRuno is - as the name suggests - a plugin for decoding rtty signals transmitted on shortwave
Since rtty is a small band signal (for amateur modes 170 Hz in this plugin), the samplerate used as input for the plugin is 192000 samples/second. The plugin uses the SP1 stream, provided by the SDRuno framework, a data stream with a rate of 192000. Further filtering and decimation is dome by the plufgin. Note that on a spectrum width a width of 2 MHz, the minimum of the SDRplay devices. a signal withd a width of a few 100 Hz is hard to detect, so use the zooming facility on the main spectrum display to zoom in.
The plugin itself can be stored in the folder for community plugins
The plugin is - as other plugins - developed under MSVC. Its functioning depends on lots of other "dll's" (Dynamic Load Libraries);
If a 0x000012f error is encountered on trying to load the plugin, it means that dll's from the Visual C++ Redistributable(VS 2015) are not found.
RTTY can be heard (a.o) around 14080 Khz. The signal is a phase shift keying signal, a signal a mark and a space signal. While on e.g. 4583 these is a signal with nautical information with a shift of 850 Hz between the mark and the space signal, signals from amateurs ususally have a shift of 170 Hz.
As seen, the plugin has a number of comboboxes with which shift, baudrate etc can be set, default settings are for the signal aas appearing in the amateur bands.
Tuning to amateur signals, e.g. around 14085KHz, requires some training. The large spectrum display is 62.5 KHz, the shift of most rtty transmissions in amateur bands is 170 Hz, so while one can - usually clearly - see the signal on the big screen, tuning to app the middle between the mark and space signal is not always easy. Happily, the SDRuno platform provides a "zoom" function on the main spectrum display, and a smaller display with a button to zoom in. As can be seen on the picture, the zooming factor choosen was such that the spectrum showed 1.6 Khz, and the mark and space signals are clearly recognizable around the center, i.e.the "0".
The rtty plugin has a combobox with which the afc can be set. The picture shows that the afc is on, and the computed frequency offset (used for correction) is 7 Hz, the remaining frequency error (the second label) is then zero.
The easiest way to tune is by coarse tuning on the main display, and - looking at the soom display - adapting the frequency with the mousewheel.
While most amateur transmissions use a shift of 170 Hz and a baudrate of 45, there are other transmissions on shortwave that use different shift/rate pairs. On 4583 e.g. there is a transmission with some nautical information that uses 850 Hz as shift, a baudrate of 50 and with the mark and space signals reversed.
The implementation of the decoder is taken from the rtty decoder of the swradio-8 implementation.