4 ms·

Not sure I understand the I/Q comment. What would the phase shifter do to the signal? Just overlap I on top of Q?

• mikewarot 2y ago
  If you only have a real signal, you're going to have to delay it 90 degrees to get the imaginary part before you do any frequency shift or filtering if you want to avoid image frequencies, negative frequencies, etc. Digital Signal processing is far easier if you have a complex signal. Without it, any frequency shift results in 4 output frequencies, f1+f2, f1-f2, f2-f1, and -(f1+f2), it gets geometric quite quickly. Things are much simpler when you have a good I/Q stream to work with. You do a complex multiply and it's always f1+f2
  • Neywiny 2y ago
    I understand that. Why do you think this isn't already a good IQ stream? The max2830 has the 90 degree hybrid built in (like every IQ demodulator I've ever seen)
    • mikewarot 2y ago
      Because at baseband they go around the max2830. A 90 degree hybrid for 100 khz all the way to 25 mhz isn't going to be small, so I can see why they didn't include it.
      • Neywiny 2y ago
        Ah. I missed that. But you wouldn't put a filter, you'd do what's called digital downconversion or DDC. This is doing the IQ demodulation in software. It's not a phase shift, it's a different type of block.