Guy K2AV and Dave AB7E! Your comments are incredibly helpful. I and many others would be very grateful if you would post all your Config setting related to coping with RX mush.
73, Dick WC1M 73, Dick WC1M > On Mar 3, 2017, at 1:59 PM, David Gilbert <xda...@cis-broadband.com> wrote: > > > I agree with your comments. Thanks for the clarifications! > > And I did indeed forget to mention the attack/decay speed influences. I even > posted comments here about that myself back shortly after I bought my K3 ... > that the time rate of change in gain is itself a non-linearity. I think my > settings are similar to yours (too lazy to check right now). > > 73, > Dave AB7E > > >> On 3/3/2017 11:28 AM, Guy Olinger K2AV wrote: >> There is some conflation of two quite different concepts going on here. >> >> The first thing you need to know about an AGC response graph is the speed >> that the incoming signal was varied to produce the curve. In many cases, the >> input signal was steady state from a signal generator, set to a list of >> input levels, observing output levels, both recorded in Excel, and the >> resultant data pairs used to create a graph line. In this case the input >> variation speed is zero. This is a static analysis. >> >> If the input signal was **amplitude**-swept at audio rates, and together >> with the output signal, used to provide the X, Y values to drive an >> oscilloscope, then you have a dynamic analysis. >> >> At this point it is good to make a note of what test equipment you are >> familiar with that will provide an **amplitude**-swept, steady frequency >> signal. >> >> Inferences from a static AGC analysis and AGC induced IMD are apples and >> oranges. >> >> The second thing that bears heavily is the attack and decay speeds. >> >> Attack speeds are usually quick. If the attack and decay are **BOTH** quick, >> and that actual attack/decay is at an audio rate, then there is a case for >> distortion, because the variable gain can actually work at an audio rate. >> >> The question is whether the attack/decay cycle can continuously recur >> because the decay goes down as fast as the attack goes up, then intermod is >> indeed possible on a grand scale. However if the decay effectively holds the >> AGC gain level at a point set by the attack, delaying even as little as 100 >> milliseconds, then the AGC cannot create audio distortion products except >> very short low frequency distortion products only at AGC attacks. >> >> Since well before the significant AGC changes in firmware 4.7x (or whatever >> that one was), I have been running my slow AGC (CONFIG: AGC-S) at maximum >> fast, and my fast AGC (CONFIG: AGC-F) at maximum slow. In retrospect, that >> was probably why I never heard the stuff that a lot of people were >> complaining about. >> >> In contests I always use my max fast setting slow AGC, and back off the RF >> gain when I have primarily very loud signals in pile-ups to get the signals >> out of hardware AGC range, which has zero intelligent tweaks available. >> >> [And yes I have just about guaranteed pile-ups in contests with for-credit >> USA to USA QSO's, because of RBN spots which pick up everyone. Those are >> "spotting pile-ups" and assisted or unlimited class folks using point and >> click on the band map or control characters to move to the next unworked >> station.] >> >> My exception to using max fast setting slow AGC is when I'm trying to copy >> through lightning static, and need to hear weaker stations down in between >> the crashes. Then I use my max slow setting fast AGC. >> >> To summarize, in order for AGC to create audio distortion products strictly >> from the AGC, the AGC must be responding at an audio rate. Frankly, why >> would anyone want to set it that way escapes me. >> >> To Wayne, I would like to be able to set a minimum hold for fast AGC as >> well. That with a fast decay, would be better than what we have. >> >> Decay rate is something left over from analog days, when the way you decayed >> AGC was letting a capacitor discharge. >> >> 73, Guy K2AV >> >> On Fri, Mar 3, 2017 at 3:02 AM, David Gilbert <xda...@cis-broadband.com >> <mailto:xda...@cis-broadband.com>> wrote: >> >> >> I've had my K3 since 2008 or so, and over the years I've seen >> people describe different forms of "mush". One set of comments >> indeed involved complaints about the hard limit at the upper end >> that has nothing to do with AGC. It is, as you say, simply a hard >> limit ... pretty much a clipper to protect the ears (and maybe >> also to help protect the output stage in the speaker driver before >> that issue got addressed). That creates a distortion, but it's >> not really what I would describe as "mush." >> >> The nonlinearity I described in my earlier post was at the >> opposite end of the curve ... down where the AGC just begins to >> kick in. As W6LX says, it's a nonlinearity in the curve, and no >> matter what you call it that contributes to the generation of >> mixing products from multiple signals that happen to be at roughly >> the same level within the passband. The low end of Jack Smith's >> plots showed that pretty clearly. During some of my contest runs, >> individual signals were perfectly clear and distinguishable, two >> not terrible, but even three signals could generate enough mixing >> products to cause problems if they were low enough in volume and >> close enough in frequency. Since I typically operate with a very >> narrow passband (about 150 HZ on CW), the mixing products end up >> very close to the real signals. For example, 2x500Hz - 510 Hz >> gives another phantom signal at 490 Hz. Things get really messy >> with three or more signals. >> >> It is also, possible, of course, to get mixing anywhere there is a >> knee in the AGC curve, but if you put the knee up higher there is >> less likelihood that multiple signals will be of the same >> amplitude to cause a problem (one will dominate), and their >> amplitude swings will range further afield of the knee ... meaning >> that a lower percentage of the energy will be mixed. At the low >> end, you're pretty much screwed ... any signal you hear will be at >> that nonlinearity and the amplitude swings will be small enough >> that they spend all their time in the nonlinearity. As I said >> before, reputedly the new synths greatly improve this. >> >> The bottom line is that if you have two or more signals within a >> passband that traverse a nonlinearity, you get mixing products >> within the same passband that blur the individual signals ... >> i.e., "mush." And since the mixing products on CW only occur when >> both (or more) of the signals are keyed, the mixing products >> aren't even intelligible. ;) >> >> At least this is how I understand the situation. I'd be happy to >> get corrected if my comments are flawed. >> >> 73, >> Dave AB7E >> >> >> On 3/2/2017 3:19 PM, Don Wilhelm wrote: >> >> >> Now that you mention hard limiting, there is a limiter in the >> K3 that if turned on will protect your ears. I am wondering >> if some instances of reported receiver mush did have limiting >> set on - that would be particularly true for those who chose >> to ride the RF Gain and/or run with AGC off. >> >> 73, >> Don W3FPR >> >> On 3/2/2017 3:37 PM, ab2tc wrote: >> >> Hi, >> >> Where in Smith's article does it say that AGC with the >> slope set for 15 acts >> as a hard limiter? There is a huge difference between AGC >> action (which is >> simply a reduction in gain with linearity retained) and >> hard limiting. >> >> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> <http://mailman.qth.net/mailman/listinfo/elecraft> >> Help: http://mailman.qth.net/mmfaq.htm >> <http://mailman.qth.net/mmfaq.htm> >> Post: mailto:Elecraft@mailman.qth.net >> <mailto:Elecraft@mailman.qth.net> >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to k2av....@gmail.com <mailto:k2av....@gmail.com> >> >> > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
