Post by mdunn on Oct 22, 2005 7:48:04 GMT -5
First I would like to compliment you on a great website! I really appreciate the intuitive approach rather a strictly mathematical one.
I do have a question, however, on something that is confusing me. In your Tutorial #8 "All about Modulation Part 1" when you go through the example of QPSK I get confused on page 18. In this page, specifically step 3 you mention that the I channel is multiplied by a cos. What confuses me is that when looking at Figure 19 the phase of the I channel modulated signal is having an abrupt phase changes even though the I bit isn't changing i.e. between 500 and 650 (the I bit is staying at -1) or 325 and 400 (the I bit is staying at 1) or conversely in the Q channel between 400 and 500 (Q bit staying at -1) or 700 and 750 (Q bit staying at 1). I'm sure there is something obvious I am missing. In step 3 you even write that for the I channel the "signal transitions at symbol bit boundaries are solely due to I channel amplitude changes". When you multiply the I channel by a cosine I would not expect aprupt phase changes expept when the I bit changed state (1 to -1 or -1 to 1) and then I would expect a 180 degree shift. What am I missing?
I do have a question, however, on something that is confusing me. In your Tutorial #8 "All about Modulation Part 1" when you go through the example of QPSK I get confused on page 18. In this page, specifically step 3 you mention that the I channel is multiplied by a cos. What confuses me is that when looking at Figure 19 the phase of the I channel modulated signal is having an abrupt phase changes even though the I bit isn't changing i.e. between 500 and 650 (the I bit is staying at -1) or 325 and 400 (the I bit is staying at 1) or conversely in the Q channel between 400 and 500 (Q bit staying at -1) or 700 and 750 (Q bit staying at 1). I'm sure there is something obvious I am missing. In step 3 you even write that for the I channel the "signal transitions at symbol bit boundaries are solely due to I channel amplitude changes". When you multiply the I channel by a cosine I would not expect aprupt phase changes expept when the I bit changed state (1 to -1 or -1 to 1) and then I would expect a 180 degree shift. What am I missing?