USRP B200 Measurements

Measurements of the USRP B200

B200 output spectrum

Setup

The ODR-mmbTools have been used to generate a DAB transmission with the B200, which was connected to a R&S spectrum analyser.

Versions used:

• 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.

Measurements

All measurement data, parameter and spectrum plots are packaged together: B200-measurements.zip

The meas-parameters.csv file describes the dabmod parameters

• master_clock_rate
• sample rate
• gain mode
• digital gain
• analog TX gain

used for each generated image.

Observations

• 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.

Conclusion

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

The effect of the FIRFilter still has to be measured.

A real world will certainly offer us more insight into these parameters.