Hi,
Maybe have a look at the datasheet of the obsolete for years Plessy
sl621 AGC chip. I have seen a discrete transistor version published
somewhere, however it is not simple using about a dozen transistors!!
Cheers,
Will
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On 09/05/2017 11:27 PM, Weddig, Henning-Christof wrote:
Concerning control loop? instabilities:
my post was just a general warning to possible instabilities, as i know
from experience when working in my old QRL about 30 years ago on such
problems within a commercial main maritime receiver (Hagenuk RX 1001M 10
kHz to 30 MHz).
In contrast to its predecessor (RX1001) the actuator was placed in the
module in front of the filterbank (xtal filters of various bandwidth,
minimum 6 pole filters).
In this configuration the AGC control loop got unstable if narrow
bandwidth filters were used. The cure was a so called lead lag filter in
the AGC control loop, eliminating the extra negative phase shift by
partly introducing a positive phase shift, but also affecting the high
frequency ripple of the filtered AGC voltage.
I am not an expert in control theory but just wanted to show that to
construct a fast attack acting and slow decay (with a hang time in
between of severals 100 ms not only some milliseconds) is not an easy
task!!
In addition this type of control loop is non-linear or should I say
"dB-linear"?
Henning
