[digitalradio] Dev: Real to I/Q

2007-10-15 Thread Rud Merriam 
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

Re: [digitalradio] Dev: Real to I/Q

2007-10-15 Thread John B. Stephensen 
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