USRP B200 Measurements
Measurements of the USRP B200
The ODR-mmbTools have been used to generate a DAB transmission with the B200, which was connected to a R&S spectrum analyser.
- ODR-DabMux v0.6.0
- ODR-DabMod v0.4.3
- UHD release_003_007_000
The USRP B200 was connected over USB2.0 to a thinkpad T420, and was externally powered using a 6V laboratory power source.
The meas-parameters.csv file describes the dabmod parameters
- sample rate
- gain mode
- digital gain
- analog TX gain
used for each generated image.
- digital gain* of 1.0 or *gain mode* 0 lead to spurious signals.
This can be due to clipping in the digital domain.
Some *master_clock_rate* settings are better than others. The decimation factor N = master_clock_rate/sample rate is the important parameters.
For N = 5 (10240000), 6 (12288000), 10 (20480000) and 15 (30720000), we see ugly shoulders next to the transmission.
For N = 8 (16384000), 12 (24576000) and 16 (32768000) the ugly shoulders are not present. N = 4 and below doesn't work.
The analog *TX gain* has to be above 35, but at about 80 we start seeing the shoulders increase. The best value for this parameter has to be found experimentally, in a complete transmitter setup, but is likely to be between 70 and 85.
The best settings seem to correspond to
- gain mode = 2
- master_clock_rate = 32768000
- native DAB sample rate of 2048000
- digital gain = 0.8
- tx gain at most 80
A real world will certainly offer us more insight into these parameters.