On Jun 6, 2007, at 9:16 PM, Jan Erik Holm wrote:
Lets hope Elecraft got it right!
/SM2EKM
-------------------------------------
Sherwood Engineering just put up their Dayton 2007
presentation on DSP and how it isn't everything it is
cracked up to be. See:
http://www.sherweng.com/documents/Dayton2007w.pdf
The thing is, what he is talking about would be very easy to fix. You
just need a smoothing algorithm to keep your AGC from responding to
transients by slewing too rapidly. Smoothing algorithms are easy to
do. Here is one:
AGC' = 0.9 * AGC + 0.1 * signal
What the above says is:
take 1/10 of the signal level (signal) and add it to 9/10 of the
previous AGC value to produce the new AGC value. We change the
response time by varying the ratio. Want faster AGC? Do this:
AGC' = 0.5 * AGC + 0.5 * signal
Want really slow AGC? Do this:
AGC' = 0.99 * AGC + 0.01 * signal
By changing the coefficients depending on whether signal is greater
or less than AGC you can change attack and decay times. Here:
if (AGC < signal)
{
# Attack
AGC = 0.9 * AGC + 0.1 * signal;
}
else
{
# decay
AGC = 0.99 * AGC + 0.01 * signal;
}
This is a really simple problem and I have a hard time believing that
this is the real problem. You want the AGC to prevent the A:D from
clipping but just barely. That will give you the maximum dynamic
range. If the A:D is allowed to clip then all bets are off.
I just have a hard time believing that any competent engineer would
fail to understand this.
73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
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