RX IQ data phase angles

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norsecode
Posts: 3
Joined: Fri Jan 06, 2017 11:45 am

RX IQ data phase angles

Post by norsecode » Tue Jul 16, 2019 4:29 am

Hi,

I am new at this and been searching the forum but can't seem to find any threads on this. Please point me to one if it exists.
I have generated IQ samples and using the bladeRF board to both transmit and receive.
I'm trying to create BPSK modulation, so I have fixed my IQ values at 500. So "0" is encoded as I=500, Q=0 and "1" is encoded as I=-500 and Q=0. Hope this is the correct way of thinking about it. My IQ files basically contain these entries (0x0F0F):

Code: Select all

500, 0
500, 0
500, 0
500, 0
-500, 0
-500, 0
-500, 0
-500, 0
500, 0
...
..

When I plot the magnitude and angle of the received samples I get this (pretty close to what I expect)
Image

No, I'm trying to do the same in an FPGA and send the samples to the RF chip. I am getting something very different. Does the plot tell anyone here what might be wrong? As far as I can tell by sending 0xFFFF in one session and 0xFFF0 in another, the inner "ring" seems to present "0" and the outer ring "1".
Image

I have tried to compare the registers between my custom setup and the BladeRF card and can't really find any big differences. Using different PAs and different charge pump currents ( I am using defaults). Have I misunderstood how to generate IQ samples?
Any help would be greatly appreciated.

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