stevecrmParticipantstevecrm September 11, 2018 at 9:34 am
I’m using the API to pull raw IQ samples and I couldn’t find the A/D output range in the manual.
I’m trying to troubleshoot some things and one thing I notice is that my IQ samples have suspiciously low values.
I’m putting in a ~2MHz wide QPSK signal at ~-30dBm, Spike gives me a nice beautiful constellation so I know my signal level must be good. My IQ samples range from -0.00662 to +0.006358. Is this correct? I was expecting something more like -1 to 1.
stevecrm September 11, 2018 at 9:36 am
- This reply was modified 10 months, 1 week ago by stevecrm.
For reference these are my capture settings
`bb_api.bbConfigureCenterSpan(id, 70000000, 4.0e6); //center hz, span hz
bb_api.bbConfigureLevel(id, -20.0, bb_api.BB_AUTO_ATTEN);
bb_api.bbConfigureIQ(id, bb_api.BB_MIN_DECIMATION, 4.0e6); //bandwidth hz
AndrewModeratorAndrew September 11, 2018 at 11:11 am
The I/Q data is scaled to mW. To calculate the power of any given I/Q value in dBm, use the formula
dBm = 10*log10(I*I + Q*Q)
Let me know if you have follow up questions.
MaksymParticipantMaksym January 11, 2019 at 7:13 am
Probably it formula has error.
dBm = 10*log10(mW)
dBm = 10*log10(mW^2)
May by I/Q data is scaled to mW^0.5 ?
Justin CrooksModeratorJustin Crooks January 11, 2019 at 9:07 am
I and Q values are voltage rather than power, so you have to square them to get a power unit.
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