Re: [Discuss-gnuradio] AGC settings explanation?

[Johnathan Corgan]

On Wed, Jun 17, 2009 at 08:00, Jamin Chan<address@hidden> wrote:

> I want to use AGC to control RF output level to be at a set value no
> matter what the input level.  I see the gr.agc_cc module has the
> following settings and defualt values:
> rate (1e-4)
> ref (1.0)
> gain (1.0)
> max_gain (0.0)
>
> can somebody explain what these settings do?  I assume reference sets
> the desired output level, but not sure about the other settings
> thanks

The AGC block works by measuring a smoothed power history, then
adjusting an output gain to achieve constant power.

The 'rate' parameter is the 'smoothing factor'.  This should probably
be named 'alpha', as it is the value of an exponential averaging
filter tap that calculates the running average of the instantaneous
signal power.  It has a default but you'll want to adjust this to your
signal characteristics.

The 'ref' parameter is the desired output power, and defaults to 1.0.

The 'gain' parameter should really be called 'initial gain', and is
what the gain starts at.  The default is 1.0, but is probably better
to set to 0.

The 'max_gain' parameter limits the gain so it doesn't grow without
bound if the input signal power goes to zero.

This block, as a software AGC, is only really suitable for adjusting
the dynamic range of a continuous, slowly varying signal such that it
remains constant power for the remainder of a flowgraph.  It doesn't
affect daughterboard gain, and doesn't work well for bursty signals.

Johnathan