[Discuss-gnuradio] confusion about set_rx_freq()

[Sachi]

Hi, Matt and Eric

Today when I looked at the wfm_rcv_gui.py code again,
I suddenly got confused by the IF frequency we used.

Suppose the FM station we are interested in is
centered at 100MHz, then for the 64MHz ADC, it should
be mapped to 100-128 = -28MHz, right?

My confusion is here: src.set_rx_freq (0, IF_freq).
If I remember correctly, Matt has told me that when we
use a negative frequency here, we actually move the
positive IF band "Down" to baseband.  So my
understanding is, if we use -28MHz here, we move
something around 28MHz, downto baseband.  But what we
should do is to use set_rx_freq(0,28MHz) to move the
band around -28MHz, "Up" to baseband.  Otherwise, we
invert everything.

Could you please help resolve my confusion? Or do I
make any mistakes here?

Thanks

Sachi


                
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