New K3 Firmware: Pileup-inspired AGC changes
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New K3 Firmware: Pileup-inspired AGC changes
 
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Anyone care to take a guess as to how long an anomoly like this would live in any other mass produced HF transceiver?
My guess - the life of the radio. Maybe the Flex guys would get to it. With Elecraft, the issue was identified on the weekend, and here it is Wednesday of the same week, the engineers understand the effect and offer test software for it. Kudos! [Elecraft] New K3 Firmware: Pileup-inspired AGC changes wayne burdick n6kr at elecraft.com Wed Feb 25 13:45:20 EST 2009 There's been a lot of discussion recently about what happens to multiple closely spaced signals with AGC turned on. We have a new field-test firmware revision available that offers a significant improvement in such situations by reducing the IMD caused by conventional AGC. If you'd like to try it, please send an email to n6kr at elecraft.com. Details: Some operators described a "merging" of multiple, close-spaced signals when listening to pileups, making individual signals hard to copy. Assuming that a narrow crystal filter is in use (close to the DSP bandwidth), this is not "desense". In most cases, we've discovered, the cause is IMD (intermodulation distortion) related to the AGC algorithm. To simulate what happens under pileup conditions, we combined four crystal oscillators with gaps between them of 5, 6, and 7 Hz (a total spread of 18 Hz for the four signals). We then injected the signals into the K3 at an equal level of about S5 and used spectral analysis to examine what happens to the passband. With AGC-F turned on (AGC fast, set to the K3's factory defaults), IMD products came up some 20-25 dB as compared to AGC OFF. The situation could be far worse in an actual on-air situation with more signals, noise, and key clicks. (AGC-S makes only a small improvement.) We ran the same test on several other radios, and verified the AGC-induced IMD characteristics are similar. IMD is generated because AGC can cause mixing between the tones and their harmonics. The faster the decay rate, in general, the more products will be generated. With just one or two signals, most products will be outside the DSP's narrow IF or AF passband. But in a pileup, where signals are greater in number and can be nearly on top of each other, there are many more opportunities for signals to combine. This results in IMD products spaced at 1 to 20 Hz, depending on the time constants, location of the signals, etc. Turning AGC off is one strategy that operators have traditionally used to combat the effects of AGC modulation. It then becomes necessary to "ride" the gain controls. Neither Lyle nor I have that much patience :) So we took a different approach: keep the AGC on, but reduce its modulation effects to negligible levels by adding a very long "hold" time. In the field-test firmware, two changes have been made. First, the AGC HLD menu setting, which used to apply only to voice modes, now applies to CW as well. (It still only affects AGC-S, the slow AGC setting.) Second, we increased the range of AGC HLD to facilitate experimentation. What we found is that an AGC hold time of about 1 second, combined with a slower AGC-S decay time, reduces in-band IMD with closely spaced signals by 20-25 dB, making it very similar to turning AGC off. The *attack* time is unaffected, so there is no "thumping" as you might have with audio-derived AGC. Any new signal peak above the one that starts the "hold" timer will restart the timer. This "hold" AGC appears to be useful in many listening situations. It can make voice signals sound cleaner, as well; after all, a voice signal can have many components, and AGC-induced modulation can add IMD products. It also helps with noisy band conditions. The down side to AGC "hold" is that large signals can charge it up to a high level, reducing gain for the duration of the hold time. But in many cases this is far preferable to the AGC IMD effects, especially if you're listening to many signals at similar amplitudes -- as in a pileup. 73, Wayne, N6KR Lyle, KK7P ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: New K3 Firmware: Pileup-inspired AGC changes
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Don Rasmussen wrote:
> Anyone care to take a guess as to how long an anomoly like this would live in any other mass produced HF transceiver? > > My guess - the life of the radio. > > Maybe the Flex guys would get to it. > > With Elecraft, the issue was identified on the weekend, and here it is Wednesday of the same week, the engineers understand the effect and offer test software for it. > > Kudos! > FT-1000MP suffers from the same (lets call it) AGC IMD. On the MP I have noticed it myself and others too but it is not widely written about. Very glad to see that it possibly can be fixed on the K3. 73 Jim SM2EKM ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Like everything else about the nasty key-click generator FT-1000MP, it's left to the customer to find and fix any problems. Yaesu did nothing about the key clicks for at least 13 years (beginning with FT-1000D until a production change for the MP in 2003)...and Yaesu is now reliving design problems with the roofing filters in the FT-2000. BTW Inrad did implement fixes for both the MP's clicks and the AGC problem (the customer must pay for all Yaesu design errors, of course): "FT-1000MP AGC Improvement Mod Some operators on major DX-peditions have complained about poor readability in large pile ups. From a joint effort between Inrad and some of these operators, we are now offering the AGC mod which improves readability somewhat for both CW and SSB. Details of the history is included in the mod instruction sheets. This new mod increases the decay time, which in the FT-1000MP is so fast that weaker signals can come up to full output between dots and dashes (or speech peaks), causing poor readability in pile ups. It also uses a damping resistor to eliminate a slight over shoot. Please be aware that under "normal" or "average" operating conditions, this mod will make very little discernible difference." The AGC mod is not applicable to the Mark V." http://www.inrad.net/product.php?productid=86&cat=10&page=1 What a horrible contrast Yaesu was to my very pleasant experience with Elecraft! 73, Bill |
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In reply to this post by Don Rasmussen
--- On Wed, 2/25/09, Jim Brown <[hidden email]> wrote: > > Someone just posted that they had trouble in pileups during > the contest > last weekend, but the radio worked better when they turned > on the > attenuator and turned down the RF gain. DUH! I learned > that in 1957 -- > but younger operators never learned it, since modern radios > depend so > heavily on AGC. Nothing personal Jim, but your post is a handy one to add to. I've been licensed for over 50 years so I've been through all of the turn off the AVC (dating myself) and ride the rf gain control business. But I must say that having to turn off the AGC and ride the rf gain control in a modern whiz-bang super-duper multi-kilobuck radio seems oxymoronic to me. Why should I have to ride the gain? I thought all of this DSP stuff was supposed to be smarter than I am. Shouldn’t the radio be smart enough to know when a signal is so strong that the attenuator needs to be inserted to "protect" the DSP or the second mixer, for example? Besides the K3 AGC appears to never be "off" despite what the display reports. For example while listening to a strong AM broadcast station, if I reduce the RF Gain* with the AGC on so that the S-meter stops peaking# and adjust the audio gain for comfortable listening and then turn the ACG off, the signal practically disappears. If the AGC was truly off then there shouldn't be any change. Adjusting the RF Gain higher to bring back the signal level will also result in the S-meter following the signal peaks. Running this experiment also seems to demonstrate a problem with the gain distribution in this radio. If I reduce the RF Gain to the point that the S-meter is just beginning to be affected, there is a distinct reduction in the SNR. It's quite disconcerting to have a S9+50 dB, interference-free signal that sounds noisy. Comparing to my TS870 with the same signal, I can decrease the gain (increase the S–meter reading) by at least 20 dB without noticing any reduction in SNR. * RF Gain seems to be a misnomer; unless I'm mistaken (always a possibility) there isn't a gain-controlled RF amplifier in the radio. The only hardware that is obviously gain-controlled is the second stage in the first i-f amplifier. # I'm seeing 5 to 6 dB of increase in meter reading between no modulation and modulation peaks. I guess I'm old fashioned but I thought that the AM carrier strength should set the AGC level. This peak-reading AGC may also be a contributor to the distorted audio that has been widely reported. Wes Stewart, N7WS ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: New K3 Firmware: Pileup-inspired AGC changes
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> # I'm seeing 5 to 6 dB of increase in meter reading between > no modulation and modulation peaks. I guess I'm old fashioned > but I thought that the AM carrier strength should set the AGC > level. It seems to me that this is exactly what one would expect. AM PEP = 4 x carrier (e.g. 6 dB). If an S-meter did not respond to peaks but rather responded to the "no modulation" signal level, it would be completely useless for CW or SSB. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Wes Stewart > Sent: Thursday, February 26, 2009 10:32 AM > To: [hidden email]; Jim Brown > Subject: Re: [Elecraft] New K3 Firmware: Pileup-inspired AGC changes > > > > > --- On Wed, 2/25/09, Jim Brown <[hidden email]> wrote: > > > > > Someone just posted that they had trouble in pileups during the > > contest last weekend, but the radio worked better when they turned > > on the > > attenuator and turned down the RF gain. DUH! I learned > > that in 1957 -- > > but younger operators never learned it, since modern radios > > depend so > > heavily on AGC. > > Nothing personal Jim, but your post is a handy one to add to. > > I've been licensed for over 50 years so I've been through all > of the turn off the AVC (dating myself) and ride the rf gain > control business. > > But I must say that having to turn off the AGC and ride the > rf gain control in a modern whiz-bang super-duper > multi-kilobuck radio seems oxymoronic to me. Why should I > have to ride the gain? I thought all of this DSP stuff was > supposed to be smarter than I am. Shouldn’t the radio be > smart enough to know when a signal is so strong that the > attenuator needs to be inserted to "protect" the DSP or the > second mixer, for example? > > Besides the K3 AGC appears to never be "off" despite what the > display reports. For example while listening to a strong AM > broadcast station, if I reduce the RF Gain* with the AGC on > so that the S-meter stops peaking# and adjust the audio gain > for comfortable listening and then turn the ACG off, the > signal practically disappears. If the AGC was truly off then > there shouldn't be any change. Adjusting the RF Gain higher > to bring back the signal level will also result in the > S-meter following the signal peaks. > > Running this experiment also seems to demonstrate a problem > with the gain distribution in this radio. If I reduce the RF > Gain to the point that the S-meter is just beginning to be > affected, there is a distinct reduction in the SNR. It's > quite disconcerting to have a S9+50 dB, interference-free > signal that sounds noisy. > > Comparing to my TS870 with the same signal, I can decrease > the gain (increase the S–meter reading) by at least 20 dB > without noticing any reduction in SNR. > > * RF Gain seems to be a misnomer; unless I'm mistaken > (always a possibility) there isn't a gain-controlled RF > amplifier in the radio. The only hardware that is obviously > gain-controlled is the second stage in the first i-f amplifier. > > # I'm seeing 5 to 6 dB of increase in meter reading between > no modulation and modulation peaks. I guess I'm old fashioned > but I thought that the AM carrier strength should set the AGC > level. This peak-reading AGC may also be a contributor to > the distorted audio that has been widely reported. > > Wes Stewart, N7WS > > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: New K3 Firmware: Pileup-inspired AGC changes
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In reply to this post by n7ws
On Thu, 26 Feb 2009 07:32:03 -0800 (PST), Wes Stewart wrote:
>But I must say that having to turn off the AGC and ride the rf gain >control in a modern whiz-bang super-duper multi-kilobuck radio >seems oxymoronic to me. Some do like to run the radio that way (W1UE guested at my QTH for CW Sprint a few weeks ago and that's how he did it), but I've never liked what I heard with the AGC off. But I DO like what I hear when I properly set RF and AF gains for the band conditions, in EXACTLY the same way that I would set the gains in the most modern and sophisticated audio mix console I use to do live recording! In the console, I set those gains for the mic I'm using on each input, what instrument/voice it will be picking up, how the musician plays (or speaker talks), how far they will be from the mic, etc. I do this to optimize that mix channel for the signal that I'm feeding it. In the K3, I'm optimizing the signal path for the range of signals it is seeing. No electronic product, and no AGC, can handle an INFINITE range -- if we want optimum performance from the radio, we must set the radio's gains to match signal conditions to the optimum range of the radio. That's nothing more than "Electronics 101!" To expect otherwise is to deny the laws of physics. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: New K3 Firmware: Pileup-inspired AGC changes
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In reply to this post by Bill W4ZV
I did that FT-1000MP mod and the improvement was marginal. It didn't correct
the problem of AGC "mush" in the passband with big pileups. Lots of IMD in big contests with that radio, too. 73, Dick WC1M > -----Original Message----- > From: Bill W4ZV [mailto:[hidden email]] > Sent: Thursday, February 26, 2009 6:32 AM > To: [hidden email] > Subject: Re: [Elecraft] New K3 Firmware: Pileup-inspired AGC changes > > > > > Jan Erik Holm wrote: > > > > Don Rasmussen wrote: > >> Anyone care to take a guess as to how long an anomoly like this > would > >> live in any other mass produced HF transceiver? > >> > >> My guess - the life of the radio. > >> > >> Maybe the Flex guys would get to it. > >> > >> With Elecraft, the issue was identified on the weekend, and here it > is > >> Wednesday of the same week, the engineers understand the effect and > offer > >> test software for it. > >> > >> Kudos! > >> > > Indeed! Just one example. As I understand this problem the Yaesu > > FT-1000MP suffers from the same (lets call it) AGC IMD. On the > > MP I have noticed it myself and others too but it is not widely > > written about. > > Very glad to see that it possibly can be fixed on the K3. > > > > > > 73 Jim SM2EKM > > > > Like everything else about the nasty key-click generator FT-1000MP, > it's > left to the customer to find and fix any problems. Yaesu did nothing > about > the key clicks for at least 13 years (beginning with FT-1000D until a > production change for the MP in 2003)...and Yaesu is now reliving > design > problems with the roofing filters in the FT-2000. > > BTW Inrad did implement fixes for both the MP's clicks and the AGC > problem > (the customer must pay for all Yaesu design errors, of course): > > "FT-1000MP AGC Improvement Mod > > Some operators on major DX-peditions have complained about poor > readability > in large pile ups. From a joint effort between Inrad and some of these > operators, we are now offering the AGC mod which improves readability > somewhat for both CW and SSB. Details of the history is included in > the mod > instruction sheets. > > This new mod increases the decay time, which in the FT-1000MP is so > fast > that weaker signals can come up to full output between dots and dashes > (or > speech peaks), causing poor readability in pile ups. It also uses a > damping > resistor to eliminate a slight over shoot. Please be aware that under > "normal" or "average" operating conditions, this mod will make very > little > discernible difference." > > The AGC mod is not applicable to the Mark V." > > http://www.inrad.net/product.php?productid=86&cat=10&page=1 > > What a horrible contrast Yaesu was to my very pleasant experience with > Elecraft! > > 73, Bill > -- > View this message in context: http://n2.nabble.com/New-K3-Firmware%3A- > Pileup-inspired-AGC-changes-tp2387110p2389115.html > Sent from the Elecraft mailing list archive at Nabble.com. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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