++++++++++++++++ See Also K2_Receiver_Images ++++++++++++++++ Date: Tue, 27 Nov 2001 10:30:47 EST From: N2EY at aol.com Subject: Re: [Elecraft] image rejection In a message dated Tue, 27 Nov 2001 7:55:22 AM Eastern Standard Time, Sam Smith writes: > I think that's what it's called :-) When you are tuning down on a band, > and all the CW notes are going up in pitch, there will sometimes be a > very strong station that goes down in pitch to nothing, and then up as > normal. That's not an image in the normal sense of the word. What you're describing is lack of rejection of the undesired sideband. > > So I'm hearing the image of the strong station. The term "audio image" is sometimes used. The -74 dB (or whatever) figure is for the RF image. For example, suppose you are listening to a signal on 7000 kHz. The LO in the K2 is at 11915 kHz or so. (7000 + 4915 = 11915. If a VERY strong signal shows up on 16930 kHz (11915 + 4915) it will be heard, too. The -74 dB figure is the amuont of rejection the 16930 kHz signal will experience compared to a 7000 kHz signal. I've never heard an audio image on a K2 that was set up properly. Improper BFO settings will allow it, though. 73 de Jim, N2EY Is this normal for the > K2 or did I goof in assembly? > > The ARRL review says image rejection (preamp off) is 74 db - the actual > number doesn't mean a whole lot to me :-) > > Sam N4MAP ++++++++++++++++++ Date: Tue, 27 Nov 2001 07:48:15 -0800 From: Vic Rosenthal Subject: Re: [Elecraft] image rejection Sam Smith wrote: > > I think that's what it's called :-) When you are tuning down on a band, > and all the CW notes are going up in pitch, there will sometimes be a > very strong station that goes down in pitch to nothing, and then up as > normal. > > So I'm hearing the image of the strong station. Is this normal for the > K2 or did I goof in assembly? 'Image rejection' usually refers to IF images. In other words, if a receiver is designed to produce a 5 MHz difference signal by mixing a 21 MHz desired signal with a 16 MHz local oscillator, you might also hear an undesired 11 MHz signal at the same place on the dial. This is not your situation. What you are hearing is an 'audio image', and probably it is because your BFO frequency is incorrect. Redo your CAL FIL procedure. 73, Vic, K2VCO Fresno CA +++++++++++++++++ Date: Tue, 27 Nov 2001 09:44:45 -0600 From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] image rejection Sam: >I think that's what it's called :-) When you are tuning down on a band, >and all the CW notes are going up in pitch, there will sometimes be a >very strong station that goes down in pitch to nothing, and then up as >normal. > >So I'm hearing the image of the strong station. Is this normal for the >K2 or did I goof in assembly? > >The ARRL review says image rejection (preamp off) is 74 db - the actual >number doesn't mean a whole lot to me :-) In this instance, it's probably not an image, but just that the station's so strong that he "leaks" past the ultimate rejection of the CW filter... The CW filter can provide only so much (ultimate) rejection... say 70dB. If the signal you're tuning thru is stronger than the available rejection, you will hear him after you tune thru him (on the other sideband). This is not unusual. Quite often it can be eliminated, or at least reduced significantly, by hitting the ATTENuator! Finally, if you have not performed the KO0B/KI6WX CW Filter Grounding Mod, I'd strongly encourage you to consider it. It's EASY to perform, NO parts, other than a couple lengths of tinned copper wire, and it can provide another 10dB (or so) of added ultimate rejection. I must add the comment that while some users have reported NO noticeable improvement, the improvement I noted in my personal K2 (s/n 00008) was well worth the small effort to perform the mod. If you cannot find a source for the mod on the Elecraft web site, I can supply it if no one else already has it available on their web site. 73 - Tom Hammond N0SS +++++++++++++++++ Date: Tue, 27 Nov 2001 11:36:46 -0500 From: "Mark J. Dulcey" Subject: Re: [Elecraft] image rejection N2EY at aol.com wrote: > > I've never heard an audio image on a K2 that was set up properly. Improper BFO settings will allow it, though. I have, but only on really strong signals. We're talking well over S9 here, and that actually means something on the K2's relatively stingy S-meter. But I prefer a relatively low CW note, which does make them a bit more likely, since it means that the audio image isn't as far away in frequency (and therefore not quite as far down the filter slope) as it would be if I used a higher note. That falls into the realm of "operator preference", not "improper BFO settings". +++++++++++++++++ Date: Tue, 27 Nov 2001 13:09:08 -0500 From: Sam Smith Subject: Re: [Elecraft] image rejection It's possible I'm using too low a CW frequency - 650 HZ. I really noticed it listening to the CQWW contest. I found the KO0B mod at this web page: http://www.rt66.com/~hypoxic/K2stuff/ultreject.html I'll try it and report back. Sam N4MAP +++++++++++++++++ Date: Tue, 27 Nov 2001 10:37:42 -0800 From: "Ron D' Eau Claire" Subject: RE: [Elecraft] image rejection Tom wrote: > In this instance, it's probably not an image, but just that the station's > so strong that he "leaks" past the ultimate rejection of the CW filter... I've heard that too, if I choose a low sidetone frequency. I happen to like to listen to beat notes in the range of 400 Hz. That's too low for the filter to provide full rejection of the signal on the other sideband near zero beat. A very strong station will occasionally be heard for a couple of hundred Hz on the "wrong side". Ron AC7AC K2 # 1289 ++++++++++++++++++ Date: Tue, 27 Nov 2001 15:53:59 -0500 From: "David A. Belsley" Subject: Re: [Elecraft] image rejection Sam: 650 Hz is not at all too low. I use 680 Hz and all is fine. The problem is likely to be the way you have your filters set. Do you hear this using all of the filters? or only the broadest one? The broadest filter (FL1, say, at 1.5 Hz) should not be centered on your sidetone, but set up band. If you use spectrogram, you will see the edges of the filter, and you can see if the edge slips down across the zero Hz mark. If it does, or gets close, it will allow some of the other sideband to slip through. You should offset the filter so that the edge is above the zero Hz mark. Since these filters are so broad, it won't harm your signal at the sidetone frequency. best wishes, dave belsley, w1euy +++++++++++++++++++ Date: Tue, 27 Nov 2001 13:20:49 -0800 From: Phil Wheeler Subject: Re: [Elecraft] image rejection Sam Smith wrote: > > It's possible I'm using too low a CW frequency - 650 HZ. I really > noticed it listening to the CQWW contest. > I use 600 Hz and do get single sideband (no images) reception .. with both the K1 and K2. I suspect the suggestion is that it relates to BFO settings is on target. Phil ++++++++++++++++++++=