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:[email protected]] Sent: Thursday, February 19, 2009 1:35 PM To: Jim Brown; [email protected] 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: [email protected] To: [email protected] 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
