You may be thinking of mixing the real signal with cosine and sine signals at 1/4 the sampling rate. The sequence can be +1, 0, -1, 0 and 0, +1, 0, -1 for cosine and sine or +1, +1, -1, -1 and +1, -1, -1, +1. In the first case, computation can be minimized if the next stage is a FIR filter as all the odd taps are zero in one channel and all the even taps are 0 in the other.
73, John KD6OZH ----- Original Message ----- From: Rud Merriam To: digitalradio@yahoogroups.com Sent: Monday, October 15, 2007 22:04 UTC Subject: [digitalradio] Dev: Real to I/Q How do I change from a real signal to quadrature? I know I have read how to do this but cannot find a reference that goes beyond multiplying by cos/sin to get I/Q. I seem to recall a trick with alternating sign sequence of 1's. I actually implemented the cos/sin technique but get 0s in alternating values so if I decimate to reduce the frequency on of the complex values is going to become 0, so it does not seem right. Also, do I remember that after the conversion the sampling rate is 1/2 the original sampling rate? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net