Bitrates

Example configurations:

desired bitrate	sample rate	samples per symbol	modulator sensitivity h=1	h=0.5
50kbps	200k	4	0.8	n/a
50kbps	250k	5	0.62	n/a
50kbps	400k	8	0.4	n/a
50kbps	500k	10	0.4	n/a
50kbps	800k	16	0.2	n/a
50kbps	1000k	20	0.15	n/a
50kbps	1.6M	32	0.15	n/a
100kbps	400k	4	0.8	0.4
100kbps	800k	8	0.4	0.2
100kbps	1000k	10	0.312	0.156
100kbps	1.6M	16	0.2	0.1
100kbps	2.0M	20	0.156	0.078
100kbps	3.2M	32	todo	todo
200kbps	800k	4	0.8	0.4
200kbps	1000k	5	0.62	0.312
200kbps	1.6M	8	0.4	0.2
200kbps	2.0M	10	0.312	0.156
200kbps	3.2M	16	0.2	0.1
200kbps	4.0M	20	0.156	0.0.78

Modulator sensitivity is only concern for transmitter deviation. h is modulation index, the ratio of (FM) frequency deviation to bit rate.

Different combinations of sample rate and samples per symbol is given because different RF bandwidths may be desired, or radio hardware is only capable of certain sample rates. Yet the newer SDR hardware has more flexible PLL clocking and should be more capable than this table.

Because bit rate is fixed to sample rate, its critical to ensure that the desired clock rate is actually selected on hardware, especially with older hardware without PLL clocking.

When using modulator sensitivity >= 0.8, take care of drive level into radio sink device (IQ baseband complex).

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This following table for 300kbps is for (older) hardware not capable of 1.2Msps, 1.5Msps, 1.8Msps etc, resampler is used.

desired bitrate	sample rate	samples per symbol	modulator sensitivity h=0.5	resampler RX
300kbps	1.6M	4	0.385	interp:6 decim:8
300kbps	2.0M	5	0.2	interp:6 decim:5
300kbps	3.2M	10	0.16	interp:15 decim:16
300kbps	4.0M	12	0.13	interp:10 decim:9
Rational resampler can be used if hardware sample rate wont achieve desired bit rate.

RX example is when hardware is sampling at 1.6Msps, but 1.2Msps is desired but cannot be precisely achieved. Rational resampler is configured interpolator to 6 go up to 9.6Msps, and then decimate 8 to 1.2Msps, the sps=4 gives 300kbps.

For transmit the interpolator value is swapped with decimator.