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[Discuss-gnuradio] Understand AM signal reception -- No Q component ??

From: senthil murugan
Subject: [Discuss-gnuradio] Understand AM signal reception -- No Q component ??
Date: Sun, 25 Mar 2012 11:11:02 +0530

Hi all,

I have some doubt in understanding working principle of usrp. I just want to confirm my understanding:

1. I have AM modulated singnal x(t)cos(2*pi*fc*t) and i am receiving that signal in antenna.

2. In Daughter board, this signal is multiplied by cos(2*pi*fc*t) and sin(2*pi*fc*t) in two separate branches (assuming Direct conversion -- Baseband conversion)

3. Branch 1: x(t)cos(2*pi*fc*t) * cos(2*pi*fc*t) --> LPF --> x(t) --> FPGA

4. Branch 2: x(t)cos(2*pi*fc*t) * sin(2*pi*fc*t) --> LPF --> 0 (since cos and sin are orthogonal) --> FPGA

5. Since Daughter board is doing direct conversion, no mixing in FPGA (i.e) in DDC.

6. In PC, I will have I component as x(t) and Q component as 0 for AM modulated signal.

Is my understanding correct?

Similarly if I take OFDM modulated signal -- xr(t)cos(2*pi*fc*t) - xi(t)sin(2*pi*fc*t) -- output at Daughter board will be xr(t) at I component and xi(t) at Q component. This will be send to PC. Is it correct?


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