PSK31 & DM780
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This probably more DM780 related than K3 but as a newbie to digital modes I thought it might be related. Then again it may be my soundcard too.
Has anyone else using DM780 with a K3 noticed that very strong psk sigs produce other images on the waterfall? It is about 2k further up or down from the original signal and can be decoded on the screen although weaker. I'm also running LP-Pan but don't notice the images on the panadapter. Also related, do strong signals wash out the waterfall display so that weaker ones vanish? I do center signals I wish to work and cut the filter down to 500hz or so to avoid strong signals in the passband and most of the time it works great. I'm just wondering if this seems normal to everyone else or do I have something adjusted incorrectly? Overloading my soundcard maybe? Transmit seems to work FB as I get good signal reports (stating my signal looks clean) and I'm seeing IMD measurements ranging from -28 to -31 on the KK7UQ IMD meter. Thanks & 73, Dave W8FGU ______________________________________________________________ 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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> Has anyone else using DM780 with a K3 noticed that very strong psk sigs produce other images on the waterfall? It is about 2k further up or down from the original signal and can be decoded on the screen although weaker. I'm also running LP-Pan but don't notice the images on the panadapter.
Could be LINE OUT level too high or sound card IMD. > Also related, do strong signals wash out the waterfall display so that weaker ones vanish? This is due to AGC action. > I do center signals I wish to work and cut the filter down to 500hz or so to avoid strong signals in the passband and most of the time it works great. I often narrow it down to 100 Hz and sometimes 50 Hz! 73, 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 |
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In reply to this post by Dave Van Wallaghen
On Thu, 19 Feb 2009 17:59:38 +0000, Dave Van Wallaghen wrote:
>Has anyone else using DM780 with a K3 noticed that very strong psk >sigs produce other images on the waterfall? It is about 2k further >up or down from the original signal and can be decoded on the >screen although weaker. I'm also running LP-Pan but don't notice >the images on the panadapter. That's harmonic or intermod distortion. Something in your audio chain is being overdriven. Could be the sound card. Or if it's an older K3, it could be the radio. Older versions of the K3 produce a LOT of audio distortion at the Line Out for settings of Line Out gain greater than about 10. Distortion starts showing up weakly with a setting around 5, and is bonkers up around 50. I've heard that's been fixed in recent production, but don't know what serial number. I think it's also fixed with the audio mod that you can buy. To fix your situation, first turn the Line Out gain at 3. Now, turn the sound card input gain down until you no longer see signals, then bring it back up until they all start decoding well. This same distortion vs level thing occurs on transmit, so be VERY careful not to overdrive the sound card or the radio. If you overdrive anything, you'll produce multiple copies of your own signal. One good way to set levels on your sound card is to listen to the sound card with headphones while you tell it to transmit. You should hear some extra sharpness or raspiness when the sound card level is too high. Listen carefully to it and pull the sound card playback level down until the raspiness goes away. That should be a good setting. You can also look at it on a scope and adjust the level so that there's no squaring or rounding of the top of the sine wave. Or you can crank the gain up until the waveform clips, then back it down until the waveform is half that height. All of these methods should get you to clean audio out of the sound card. Once you have that level right, hook it up to the K3, pull the Line In gain down, then bring it back up slowly as you watch the RF level. When the level stops increasing, you've gone too high. Back it off a bit. That should get you close. 73, Jim 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 |
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In reply to this post by Dave Van Wallaghen
Thank you very much Jim for the nicely detailed explanation and process. I have K3 #338 but did apply all of the applicable hardware mods to date. So hopefully the distortion is not hardware related but operator error in driving my soundcard too hard.
I will follow the process you outlined here first thing in the morning and hopefully eliminate the harmonics. And then back to happy PSK31 :-) Thanks again & 73, Dave W8FGU ------Original Message------ From: Jim Brown To: [hidden email] To: [hidden email] Subject: Re: [Elecraft] [K3]PSK31 & DM780 Sent: Feb 19, 2009 1:38 PM On Thu, 19 Feb 2009 17:59:38 +0000, Dave Van Wallaghen wrote: >Has anyone else using DM780 with a K3 noticed that very strong psk >sigs produce other images on the waterfall? It is about 2k further >up or down from the original signal and can be decoded on the >screen although weaker. I'm also running LP-Pan but don't notice >the images on the panadapter. That's harmonic or intermod distortion. Something in your audio chain is being overdriven. Could be the sound card. Or if it's an older K3, it could be the radio. Older versions of the K3 produce a LOT of audio distortion at the Line Out for settings of Line Out gain greater than about 10. Distortion starts showing up weakly with a setting around 5, and is bonkers up around 50. I've heard that's been fixed in recent production, but don't know what serial number. I think it's also fixed with the audio mod that you can buy. To fix your situation, first turn the Line Out gain at 3. Now, turn the sound card input gain down until you no longer see signals, then bring it back up until they all start decoding well. This same distortion vs level thing occurs on transmit, so be VERY careful not to overdrive the sound card or the radio. If you overdrive anything, you'll produce multiple copies of your own signal. One good way to set levels on your sound card is to listen to the sound card with headphones while you tell it to transmit. You should hear some extra sharpness or raspiness when the sound card level is too high. Listen carefully to it and pull the sound card playback level down until the raspiness goes away. That should be a good setting. You can also look at it on a scope and adjust the level so that there's no squaring or rounding of the top of the sine wave. Or you can crank the gain up until the waveform clips, then back it down until the waveform is half that height. All of these methods should get you to clean audio out of the sound card. Once you have that level right, hook it up to the K3, pull the Line In gain down, then bring it back up slowly as you watch the RF level. When the level stops increasing, you've gone too high. Back it off a bit. That should get you close. 73, Jim 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 |
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Also, don't forget that Compression is a no-no on data modes. It can cause
distortion as well. Jim K5HTK -----Original Message----- From: Dave Van Wallaghen [mailto:[hidden email]] Sent: Thursday, February 19, 2009 1:35 PM To: Jim Brown; [hidden email] Subject: Re: [Elecraft] [K3]PSK31 & DM780 Thank you very much Jim for the nicely detailed explanation and process. I have K3 #338 but did apply all of the applicable hardware mods to date. So hopefully the distortion is not hardware related but operator error in driving my soundcard too hard. I will follow the process you outlined here first thing in the morning and hopefully eliminate the harmonics. And then back to happy PSK31 :-) Thanks again & 73, Dave W8FGU ------Original Message------ From: Jim Brown To: [hidden email] To: [hidden email] Subject: Re: [Elecraft] [K3]PSK31 & DM780 Sent: Feb 19, 2009 1:38 PM On Thu, 19 Feb 2009 17:59:38 +0000, Dave Van Wallaghen wrote: >Has anyone else using DM780 with a K3 noticed that very strong psk >sigs produce other images on the waterfall? It is about 2k further >up or down from the original signal and can be decoded on the >screen although weaker. I'm also running LP-Pan but don't notice >the images on the panadapter. That's harmonic or intermod distortion. Something in your audio chain is being overdriven. Could be the sound card. Or if it's an older K3, it could be the radio. Older versions of the K3 produce a LOT of audio distortion at the Line Out for settings of Line Out gain greater than about 10. Distortion starts showing up weakly with a setting around 5, and is bonkers up around 50. I've heard that's been fixed in recent production, but don't know what serial number. I think it's also fixed with the audio mod that you can buy. To fix your situation, first turn the Line Out gain at 3. Now, turn the sound card input gain down until you no longer see signals, then bring it back up until they all start decoding well. This same distortion vs level thing occurs on transmit, so be VERY careful not to overdrive the sound card or the radio. If you overdrive anything, you'll produce multiple copies of your own signal. One good way to set levels on your sound card is to listen to the sound card with headphones while you tell it to transmit. You should hear some extra sharpness or raspiness when the sound card level is too high. Listen carefully to it and pull the sound card playback level down until the raspiness goes away. That should be a good setting. You can also look at it on a scope and adjust the level so that there's no squaring or rounding of the top of the sine wave. Or you can crank the gain up until the waveform clips, then back it down until the waveform is half that height. All of these methods should get you to clean audio out of the sound card. Once you have that level right, hook it up to the K3, pull the Line In gain down, then bring it back up slowly as you watch the RF level. When the level stops increasing, you've gone too high. Back it off a bit. That should get you close. 73, Jim 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 |
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In reply to this post by Dave Van Wallaghen
>Jim Brow wrote: That's harmonic or intermod distortion. Something in your
audio chain is being overdriven. Could be the sound card. Or if it's an older K3, it could be the radio. Older versions of the K3 produce a LOT of audio distortion at the Line Out for settings of Line Out gain greater than about 10. Distortion starts showing up weakly with a setting around 5, and is bonkers up around 50. Jim, your K3 and mine seem a bit different. Before I put the audio modification in my K3 [ser 508] I would see obvious IMD on the DM780 waterfall or Spectrumlab with Line Out set anywhere above 3, 10 was problematic. Even at 3 I could see harmonics of S9 tones. After the modification I run Line Out about 10 and see I see slight IMD above band noise 60-70dB below the carrier tone, passable. I have played with sound card gain to try and make sure that the sound card is not being over driven but I have to admit that I don't really know how to distribute the gain between the sound card and the K3 Line Out. DM780 has a soundcard Receive Signal Level; I run it in the lower 25% of the scale and seem to see nice traces. Mike Scott - AE6WA Tarzana, CA (DM04 / near LA) K3-100 #508/ KX1 #1311 ______________________________________________________________ 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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In reply to this post by Dave Van Wallaghen
>Dave Wrote...but did apply all of the applicable hardware mods to date. So
hopefully the distortion is not hardware related but operator error in driving my soundcard too hard. Dave, When I have my K3 Line Out plugged into my sound card rear microphone input I see IMD products that I don't see when I plug into the Line In on the PC soundcard. It is difficult for me to know which one I am plugged into because I do not understand the color code on the PC sound input output panel. The only way I make sure I am plugged into Line In is to bring up the Windows microphone panel and mute all inputs but Line In and make sure that I am getting a waterfall trace with only Line In selected. If no noise on the waterfall I plug into another socket until I finally arrive at Line In. I found this made quite a difference on my set up when I finally plugged into the correct place. Mike Scott Tarzana, CA ______________________________________________________________ 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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In reply to this post by Mike Scott-7
On Fri, 20 Feb 2009 10:49:40 -0800, Mike Scott wrote:
>Jim, your K3 and mine seem a bit different. Before I put the audio >modification in my K3 [ser 508] I would see obvious IMD on the DM780 >waterfall or Spectrumlab with Line Out set anywhere above 3, 10 was >problematic. Even at 3 I could see harmonics of S9 tones. I doubt that our radios were different, only a question of degree. The harmonics at an output setting of 3 were in the noise level of my measurement. For Line Out, the level of distortion at 3 (or even 5) is VERY unlikely to be a problem. >After the modification I run Line Out about 10 and see I see slight IMD >above band noise 60-70dB below the carrier tone, passable. Remember, there's a transformer in line. 60-70 dB is WAY down, and quite respectable IMD performance! Of course, I'd still like the transformers to go away. There's no good reason for having them, they add to cost, and they subtract from performance! >I have played with sound card gain to try and make sure that the sound card >is not being over driven but I have to admit that I don't really know how to >distribute the gain between the sound card and the K3 Line Out. DM780 has a >soundcard Receive Signal Level; I run it in the lower 25% of the scale and >seem to see nice traces. Some sound cards are better than others. Based on having used them with some high power audio testing software, I can say that the one in my IBM T41 is better than the one in my T22. I suggest that you run the K3 as cool as you can (that is, a low value of Line Out gain) and adjust the input of the sound card to get good decoding. 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 |
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In reply to this post by Dave Van Wallaghen
On Thu, 19 Feb 2009 17:59:38 +0000, Dave Van Wallaghen wrote:
> Has anyone else using DM780 with a K3 noticed that very strong psk sigs produce other images on the waterfall? It is about 2k further up or down from the original signal and can be decoded on the screen although weaker. I'm also running LP-Pan but don't notice the images on the panadapter. > Also check your NB settings, I've found that the more aggressively the noise blanker is working the more likely the ghost signals are to appear. OTOH, I have not yet gotten to the AF mods so I am probably seeing a combination of factors. 73, Steve AD7OG K3 S/N 1544 ______________________________________________________________ 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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Thanks for the suggestion Steve. I usually default the NB and NR off
until I need them and I rarely use them. But that makes sense. As an update to this topic, first, thanks to everyone here who made suggestions. It was a great learning experience for me. I did go back and adjust the input to my soundcard. It is on a laptop and the only input is a mic connection. Looking at the setup on the computer, I found that the gain was turned up all the way at 100% with some special processing enabled for voice. I turned it down to about 35% and disabled the special processing on the line. I also found that my CONFIG: LIN OUT was set at 20! I don't know when I did that, but I went through the setup of my soundcard as Jim described by starting out with everything at a minimum. I then brought the levels up until I could see decoding with DM780. I then wound up with the CONFIG: LIN OUT setting at 4 with good decoding and no noticeable harmonics on the screen. On my DM780 waterfall, the noise level is just visible on the bottom of the Spectrum & Grid window and weak signals are now fairly visible in the waterfall. The audio level monitor on DM780 now shows in the low 20% range as opposed to the upper 60's and occasional Overload as it did before. As a test, I then worked back to back Italian stations on 40m at 30 watts. Works for me :-) Thanks again & 73, Dave W8FGU Steve Ward wrote: > On Thu, 19 Feb 2009 17:59:38 +0000, Dave Van Wallaghen wrote: > >> Has anyone else using DM780 with a K3 noticed that very strong psk sigs produce other images on the waterfall? It is about 2k further up or down from the original signal and can be decoded on the screen although weaker. I'm also running LP-Pan but don't notice the images on the panadapter. >> > Also check your NB settings, I've found that the more aggressively the > noise blanker is working the more likely the ghost signals are to > appear. OTOH, I have not yet gotten to the AF mods so I am probably > seeing a combination of factors. > > 73, > Steve > AD7OG > K3 S/N 1544 > ______________________________________________________________ > 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 |
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