HackRF I and Q receiver output signals
Hi everyone, I have recently received an H4M kit with the HackRF One on board.
I'm trying to understand the I and Q signals that are present at the receiver. I see that they are differential outputs. When I apply a large signal in NBFM receiver mode (-47dBm,150MHz, 3kHz deviation) and I look at the I and Q lines, I see a 750kHz sine wave, 400mV pk-pk in quadrature on the receiver outputs. I understand that this is a zero IF design, is the down-conversion to baseband done digitally?
Can someone help me (a beginner with SDR) understand why the 750kHz signals are present, and not a zero IF, (which is what I was expecting)? Is it because it prevents a DC offset or have I measured something incorrectly? Is this related to the sample rate?
I am no expert on SDR code, but if i'm pointed in the right direction, I'll try to figure it out.
Thanks for the assistance!