not going to repeat what everyone has already posted:
One begins with an RF signal which has modulation (easiest to consider the modulation SSB and even easier if you take the example of a two-tone test signal for SSB).
The first step in producing IQ output is to spit the RF into two parallel mixers that use the same frequency LO, but one is shifted 90-degrees in phase. The LO is the same frequency as the RF so one gets audio as an output (same thing one does in an SSB demodulator). The two resulting audio outputs are 90-degree out of phase with each other. In the typical SDR the next step it convert to digital using a analog to digital converter (ADC)(hams are using their soundcard as a ADC). The resulting two digital signals are out of phase with each other and can be processed by a computer (called an DSP = digital signal processor).
Due to the unique mathematical properties of the two digital signals one can recover CW/DSB/SSB/AM/FM/PSK modulation types (and I may have left out others).
This is a very rudimentary (non-mathematical) description. The true beauty of using IQ is its versatility. No longer does the receiver have to have a product detector, discriminator, envelope detector, etc. The DSP does it all in digital form and re-converts the demodulated signal back to audio (or displays the signal on a screen).
http://www.kl7uw.com/MAP65.htm the diagram may help understanding. 73, Ed - KL7UW http://www.kl7uw.com "Kits made by KL7UW" Dubus Mag business: [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
