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Double sideband

Started by openshort 2 weeks ago4 replieslatest reply 2 weeks ago161 views
i am trying to understand a problem that i believe i have with my DAC setup.

I am taking a tone from a RF signal generator and capturing it using a 9002 transceiver (adc and dac).

it spits out 16bit IQ for RX and accepts 16bit IQ for tx all at basedband.

I take that same IQ data and send it back out the DAC to a spectrum analyzer. 

I see the tone offset above center freq as expected but also an equal tone at the negative offset below the center freq and its of equal power. 


The input is say a 2001 mhz signal capturing at 25 msps. then the Tx is coming out at 3300 mhz. 

I am not sure how to explain why i don't see the same signal coming out. So i am not sure where to start since i not sure what a possible problem could be.  

Is it a swapped IQ data? 


thanks

[ - ]
Reply by kazFebruary 13, 2024

you say "The input is say a 2001 mhz signal capturing at 25 msps. then the Tx is coming out at 3300 mhz.".

Can you explain such low sampling rate, are you undersampling?

[ - ]
Reply by openshortFebruary 13, 2024

yes the transceiver chip takes baseband IQ 25 msps and up converts it, filters, interpolates to get it to 2ghz or whichever freq you pick.and the reverse to go from some center freq back down to baseband. all automagically. assuming its configured right lol

my current tests lead me to think the Q data is not getting sent or read.

i guess my question is if i send an I only signal with zeros for Q then it should be symmetric correct?

I made an fs/4 tone using 4 samples and got plus and minus tones at 6.25mhz. expecting just the positive.

i got no output when i send Q data only. i.e. 0 for I and non zero numbers for Q



[ - ]
Reply by kazFebruary 13, 2024

Your conclusion that "I" only is sent to a "mixer" makes sense. Check your mixer setup if it is correct. "I" will end up mirrored if Q is null.

[ - ]
Reply by openshortFebruary 13, 2024

thank you for confirming that.


greatly appreciated