Re: [Discuss-gnuradio] Inquiry about automatic gain control

[bdannan]

Brian,

If you refer to the usrp\fpga\sdr_lib\adc_interface.v

this is a comment stating: \\level sensing for AGC
on line 67 of the verilog code file.

I have read on the wiki that AGC can be implemented by moving resistors around,
can you elaborate on this: which resistors, and on what board?

I am assuming that there is some sort of feedback loop for the FPGA to an
amplifier which uses the RSSI, is there not one? 

Thanks for your time and help.

-Benjamin Dannan

Quoting Brian Padalino <address@hidden>:

> On Mon, Dec 1, 2008 at 10:53 PM,  <address@hidden> wrote:
> >
> > I am trying to achieve a goal of controlling the AGC, please help.
> >
> > Here is what I have so far, for the automatic gain control (AGC):
> >
> > I have found in the module adc_interface (which is in
> > fpga\sdr_lib\adc_interface) a comment about level sensing for the AGC.
> >
> > I am assuming the module rssi and module adc_interface is where the AGC is
> > controlled?
> >
> > If not where do I go about turning on or off the AGC. The rssi is used to
> sense
> > the signal strength in the fpga and that is feedback to the ADC which
> controls
> > the AGC, is that correct?
> 
> I don't believe there is any AGC actually going on at all.  Please see here:
> 
>     http://gnuradio.org/trac/ticket/66
> 
> > After I know how to turn on and off the AGC, how do I adjust the gain of
> the
> > amplifier?
> 
> You need to familiarize yourself with the gain settings of the
> different daughterboards and how their gains are controlled.
> 
> The Python db code is probably a good place to start looking.
> 
> > If I wanted to make a block diagram, or refer to a schematic that involves
> the
> > AGC, where should I start?
> >
> > Is the AGC located before the ADC, and the ADC is contained in the fpga,
> right?
> 
> The ADC is an external chip.  The data feeds into the FPGA where it is
> then processed.
> 
> > Thank you so much for your time and help,
> 
> Good luck.
> 
> Brian
>