I want to capture and replicate IR signals of various electronics. There are various guides out there. However, I realize that there are various carrier frequencies, which I dont see discussed. How do I know what frequency of my target electronics in order to buy the right IR receiver and transmitter? Thanks.
You buy a common phototransistor that does not depend on a particular modulation scheme, add a biasing resistor, and observe the signal on an oscilloscope.
If you want to produce a universal remote control, you can't really make any assumptions about the frequency required.
A simple infrared photodiode will accept any frequency. It's then up to you to amplify the tiny signal they produce, digitise it and store it in memory.