Symbol Length

The -symbollength flag sets the how many samples make up each symbol and the default is 72.

The sample rate (fs) is determined from the symbol length and data rate according to the following:

fs = 32768 * Symbol Length

Rtl-sdr dongles have two ranges of valid sample rates:

225 kHz < fs < 300 kHz
900 kHz < fs < 3.2 MHz

Due to the nature of some optimizations in the decoder, symbol lengths must be multiples of 8. So there are a limited set of valid symbol lengths. They are given below:

Symbol Length	Sample Rate
8	262.144 kHz
32	1.048576 MHz
40	1.310720 MHz
48	1.572864 MHz
56	1.835008 MHz
64	2.097152 MHz
72	2.359296 MHz
80	2.621440 MHz
88	2.883584 MHz
96	3.145728 MHz

Depending on your dongle, symbol lengths above 72 may drop samples. The default 72 is a fairly reliable value for most dongles.