I think the topic I/Q modulation is damn interesting so I fiddelt a little bit around with the topic.
I/Q modulation is the summing of two amplitude modulated 90° phase shifted signals.
The experiments for an I/Q modulator started at the phase splitter, beacuse I don’t own a frequency/signal generator which can output a 90° phase shifted signal.
Phase Splitter
I’ve built the phase splitter as a lossy type with a capacitor and an inductor directly wired against some sma edge connectors.
keep an eye on the v/div
The performance isn’t quite optimal – practically 93.2° phase shift – and the lossiness results in a ten times lower signal amplitude for which I need some makeup gain. If I stick a little bit to the project, I will built one of those active ones like here. For this needs to do the job.
I came way faster back to this topic as I’ve recognized how crucial the signal amplitude of the in phase and the quadrature shifted signal is.
I found some articles about the internal construction of quadrature mdemodulators using poly-phase filters.
Poly-phase filters are simply to filters – one low-pass and one high-pass filter at exactly the same corner frequency to perfectly get the in-phase and quadrature phase signal.
So I’ve built one, but I had no matched components so I for now changed the frequency until I’ve got a component match.
