Re: [Discuss-gnuradio] AGC

[Johnathan Corgan]

Johnathan Corgan wrote:
> Matt Ettus wrote:
> 
>> I don't have the agc code in front of me, but the definition 
>> of the setpoint in important.  Assuming you make the setpoint 1, 
>> and that the agc is setting the average (of either I or Q) to 
>> the setpoint, the amplitude will go from 0 to 2, since this is AM. 
>> You will need to subtract 1 so that you get a signal of +/- 1 for 
>> the audio sink.

> Is that the case?  My brain can't seem to wrap around simple concepts today.

Matt, you're completely right.  Just adding a gr.add_const_ff(-1.0) to
the pipeline cleared it up and let the prior AGC stage operate at it's
default reference of 1.0:

# Convert baseband AGC'd (ref. val. 1.0) AM channel to audio floats
class am_demod(gr.hier_block):
    def __init__(self, fg):
        MAG = gr.complex_to_mag()
        DCR = gr.add_const_ff(-1.0)
        fg.connect(MAG, DCR)
        gr.hier_block.__init__(self, fg, MAG, DCR)

-Johnathan