++++++++++++++++++++ Date: Sat, 06 Apr 2002 13:22:26 -0800 From: "John Grebenkemper, KI6WX" To: Elecraft Mailing List Subject: [Elecraft] Improvements To The K2 SSB 2nd XFil Mod The Elecraft web site contains a modification to improve the SSB response of the K2 in receive by changes to the Second Xtal Filter on the K2 RF Board. While this change is much better than the original filter response, there is still some difference between the LSB and USB. Using some simulation software to guide me, I was able to reduce the measured SSB ripple of the Second Xtal Filter to 1 dB peak-to-peak from 4914 to 4916 kHz. Now, I can not hear any difference when switching between LSB and USB. If you want to try this change, the steps for doing it are listed below. This change has been applied to two K2's, but it has not been checked or approved by Elecraft. The change will increase the Second Xtal Filter insertion loss by 2 dB, but it will not have any effect on receiver sensitivity since this filter is at the end of the IF amplifier. The change may be installed with the following steps: 1. Install the 2nd Xfil Mod described in http://www.elecraft.com/Apps/new_fil_docs/k2_2nd_xfil_ssb_mod.pdf 2. Replace the 120pF capacitor in the above mod with a 100pF capacitor (10% tolerance or better). 3. Install a 5.6k resistor from pin 1 of U11 to pin 2 of U11 on the RF board. 4. Check the adjustment of L34. In CW mode, tune to the weak birdie heard at 7 MHz. Set the filter bandwidth to 0.1 kHz and tune L34 for maximum signal relative to the background noise. Your K2 now has a much flatter response when receiving SSB signals through the OP1 filter. A plot of the K2's Second Xtal Filter response in the OP1 setting is available on my home page at http://home.pacbell.net/johngreb/KI6WX.html . The plots were done with original filter configuration, the 2nd Xfil Mod as described on the Elecraft web site, and my change to this mod with the 100pF capacitor and 5.6k resistor. You may want to check your LSB and USB response with Spectrogram before and after the change. With my K2, the Spectrogram LSB and USB curves fall nearly on top of each other. -John KI6WX +++++++++++++++++ Date: Sat, 20 Apr 2002 09:41:30 -0500 To: elecraft@mailman.qth.net From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: [Elecraft] KS 2nd Xfil SSB Mod Folk: You may have missed John (KI6WX's) recent post regarding fruther flattening of the K2 SSB filter response. I am including it below. NOTE that John assumes that you have ALREADY made the previouly-posted "2nd Xfil SSB Mod", which also REQUIRES that RF-C180 be removed as well. So, if you are just now going to perform the mod, download the docs for the original mod from the Elecraft web site, follow them, as shown in that document, BUT use 100pF IN PLACE OF the 120pF cap originally specified and follow the rest of John's instructions. 73, Tom N0SS __________________ --- see above entry --- +++++++++++++++++++ From: "Don Brown" To: "Elecraft" Subject: Re: [Elecraft] RE: K2 SSB mod question - parts Date: Sat, 20 Apr 2002 10:21:22 -0500 Hi Gang After reading Toms post it looks like the mod has changed. OK I will supp= ly the 100 pf rather than 120 pf plus a 5.6k resistor. Same price. Don KD5NDB ----- Original Message ----- From: Don Brown Sent: Saturday, April 20, 2002 9:16 AM To: Elecraft Subject: Re: [Elecraft] RE: K2 SSB mod question - parts Hi Gang I am already making several small kits for Elecraft Radios: Speaker Grill Cloth Mod - SASE #10 Envelope Noise Generator Kit - $15 Solar Charge Controller - $25 I would be willing to put together a kit of parts for the 2nd filter mod.= 120 pf cap, .01 uf cap , 2n3904, 3.9 k resistor. How does SASE #10 envelope and $1 sound. Send to : Don Brown 19132 Falls Creek Drive Flint, Texas 75762 Thanks Don KD5NDB ++++++++++++++++++++++ Date: Sat, 20 Apr 2002 13:31:45 -0700 From: "John Grebenkemper, KI6WX" Subject: Re: [Elecraft] K2 SSB mod question - parts To: Elecraft Mailing List Kirby; Several weeks ago I published a message on the reflector about an improved version of the 2nd Xfil Mod that produces an even flatter response for the OP1 filter. On my K2 there is no change in the pitch of the background noise when you switch between LSB and USB. A frequency plot of the two responses using Spectrogram shows that they line up on top on each other. I will put the full mod up on my web site in the near future, but the summary of how to do it is below. The 120 pF cap is replaced with a 100 pF. You may still use a 120 pF, but the response will not be quite as flat; do not use a capacitor less than 100 pF (such as 82 pF) or the response will deteriorate significantly. 1. Install the 2nd Xfil Mod described in http://www.elecraft.com/Apps/new_fil_docs/k2_2nd_xfil_ssb_mod.pdf 2. Replace the 120pF capacitor in the above mod with a 100pF capacitor (10% tolerance or better). 3. Install a 5.6k resistor from pin 1 of U11 to pin 2 of U11 on the RF board. 4. Check the adjustment of L34. In CW mode, tune to the weak birdie heard at 7 MHz. Set the filter bandwidth to 0.1 kHz and tune L34 for maximum signal relative to the background noise. -John KI6WX ++++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'george winship'" , Subject: RE: [Elecraft] K2 SSB 2nd Xfil mod ? Date: Wed, 3 Jul 2002 21:14:08 -0700 Was going to do this mod but RS did not have the 120pf cap. Will 100pf work or do I need to find a 120pf? 73, George WA5UIH, K2-2217 At first I paralleled a couple of caps to make up 120 pf. But then John Grebenkemper, KI6WX, came up with a variation to the mod that produces a slightly flatter bandpass using a 100 pf cap! All you need is one more resistor at 5.6k. Make the mod according to the original instructions you have, using the 100 pf cap instead of the 120 pf cap. The 5.6 k resistor goes from pin 1 and pin 2 of U11 on the r-f board. When the mod is installed, set your CW filter narrow bandwidth to 0.1 kHz and tune in the birdie at 7 MHz. Adjust L34 for maximum signal to noise ratio. So there, you can use the 100 pf cap and get a slightly flatter response! Ron AC7AC K2 # 1289 ++++++++++++++++++ Date: Thu, 11 Jul 2002 22:41:30 -0700 From: "John Grebenkemper, KI6WX" To: Elecraft Mailing List Subject: [Elecraft] Mods To The KSB2 For the last 6 months I have worked on a set of changes to the KSB2 that provide increased SSB performance for the K2. These changes are not required for the K2 to function well in the SSB mode, but are intended for those who wish to obtain the best possible performance. There are four major changes discussed in the document. The first allows the builder to select different SSB bandwidths for the KSB2 filter. This may be especially useful if you desire a wider SSB filter. The second improves the flatness of the 2nd Xtal Filter. I had posted this change to the reflector a few months ago and several people have implemented it in their K2. The change makes the LSB and USB response in receive nearly identical. The third change increases the RF gain of the KSB2 so that it will function with lower output microphones without resorting to various resistor changes that have been tried by a number of people. It also allows the K2 to achieve a slightly higher SSB output on 10 meters. The fourth change reduces the in-band audio intermodulation distortion that occurs in the KSB2 modulator by 15-20 dB. This change is most important for data modes, but should also increase the audio fidelity of the KSB2 in SSB transmissions. All of these changes are described in a document "Improving the Performance of the KSB2" which may be downloaded from my website at http://home.pacbell.net/johngreb/KI6WX.html -John KI6WX +++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'Helmut Usbeck'" , Subject: RE: [Elecraft] 2nd XFil SSB MOD Date: Sun, 29 Sep 2002 08:17:49 -0700 It's a case of some talented ops all working to improve the rig over time , Helm. The original mod was developed by Wayne and Eric at Elecraft. Some months later John, KI6WX, did some additional testing of the original modification and came up with those changes to make the response still flatter. You can find the details along with comparative plots at http://home.pacbell.net/johngreb/KI6WX.html. Ron AC7AC K2 # 1289 ======================================================== There is a take-off on the mod that uses a 100 pf cap instead of 120 pf that the original mod describes. Also the mod with the 100 pf adds a 5.6K resistor across pins one and two of U11. I presume that this resistor is for terminating the filter. Is it really needed? If so, why not terminate the original mod the same way? Regards, Helm. WB2ADT +++++++++++++++++ Date: Sun, 29 Sep 2002 19:02:34 -0700 From: "John, KI6WX" Subject: Re: [Elecraft] 2nd XFil SSB MOD To: Elecraft Mailing List Helm; The resistor is needed to properly terminate the Xtal filter. My simulations showed that the smaller cap produced a flatter response than 120 pF used in the original design. -John KI6WX ----- Original Message ----- From: "Helmut Usbeck" To: Sent: Saturday, September 28, 2002 9:19 PM Subject: [Elecraft] 2nd XFil SSB MOD > There is a take-off on the mod that uses a 100 pf cap instead of 120 pf > that the original mod describes. Also the mod with the 100 pf adds a > 5.6K resistor across pins one and two of U11. I presume that this > resistor is for terminating the filter. Is it really needed? If so, > why not terminate the original mod the same way? > > Regards, > Helm. WB2ADT +++++++++++++++++ Date: Sat, 02 Nov 2002 10:10:53 -0600 To: Paul Saville , elecraft@mailman.qth.net From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] What's in 2nd Filter Upgrade for K2 mod kit? Hi Paul: >The spare parts and mod kits page shows a K2 2nd filter upgrade kit for >$10. What's in the kit? If it only contains the 4 parts listed in the app. >note, then it would be cheaper to buy the parts locally. But maybe it's a >bit fancier than that? It's not, and there's no reason you can't obtain the parts locally. The 'kit' was mainly for those who don't have direct access to components. The 'kit' helps to 'flatten out' the response of the SSB filter, and regardless of how/where you get the parts is WILL WORTH installing. You can find the docs for this mod posted on the Elecraft web site, at: http://www.elecraft.com/Apps/new_fil_docs/k2_2nd_xfil_ssb_mod.pdf Cheers, Tom N0SS +++++++++++++++ Date: Sat, 09 Nov 2002 07:07:10 -0800 From: lhlousek Subject: [Elecraft] Spectrogram V5 - 2nd XFIL Flattening mod To: elecraft list Without the KSB2, the filter flattening mod reduces to removal of C180 on the RF board since the transistor switches in the padding cap only when the OPT1 filter on the KSB2 is selected. I removed it and found that it lessened the filter tilt and increased USB LSB filter symmetry. Lou W7dzn +++++++++++++++ From: "Todd Gahagan" To: Date: Sun, 12 Jan 2003 12:51:39 -0700 Subject: [Elecraft] Comment on 2nd filter mod Well, after changing all the crystals and up grading the 2nd filter mod to the latest specs I honestly don't see much fattening of the filter when viewed with Spectrogram. I have checked the voltage on the transistor in the mod and it is working properly. I have changed the cap from 120 pf to 100 pf. Maybe I'm expecting too much but in looking at another K2 that has the mod without the crystal change I'm finding that mine does not look nearly as flat. Just a comment and wondering what to try next. Thanks, Todd-WA7U +++++++++++++++ Date: Sun, 12 Jan 2003 12:12:20 -0800 From: "John, KI6WX" Subject: Re: [Elecraft] Comment on 2nd filter mod To: Elecraft Mailing List Todd; The final version of the mod should produce a very flat response. See http://home.pacbell.net/johngreb/modifications_to_the_ksb2.pdf for graphs of the measured response of the second Xtal filter with the various changes. -John KI6WX ----- Original Message ----- From: "Todd Gahagan" > Well, after changing all the crystals and up grading the 2nd filter mod to > the latest specs I honestly don't see much fattening of the filter when > viewed with Spectrogram. +++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'Elecraft Mailing List'" Subject: RE: [Elecraft] Comment on 2nd filter mod Date: Sun, 12 Jan 2003 12:33:53 -0800 I'll add to John's comments to make SURE that you are picking up the audio from the Aux Speaker jack, NOT the "phones" jack. The caps in the phones output circuit in the K2 roll of the response quite a bit, giving the Spectrogram display a "tilt" that really isn't in the filters. Of course, if you took all your measurements through the phone's jack, you should see an improvement, but it won't be as flat as a lot of the images you will see of the "improved" filter. The biggest thing I noticed after installing the mod was in how the two sidebands SOUNDED, without even looking at Spectrogram. The "2nd Xfil Flattening" mod came about right after I got my K2 assembled and noticed that the two sidebands sounded totally different. Just listening to the background noise told me that one had a LOT of high emphasis that the other sideband lacked. To me, it made listening to SSB on the upper bands irritating. Then the mod appeared on the reflector here and I installed it immediately. I could still hear a slight difference in the sound of the background noise when switching from USB to LSB (that was before the more carefully matched filter crystals were available) but the audio of a SSB signal sounded the same to my ear on either sideband. Ron AC7AC K2 # 1289 +++++++++++++++++ From: "Todd Gahagan" To: , "'Elecraft Mailing List'" Subject: Re: [Elecraft] Comment on 2nd filter mod Date: Sun, 12 Jan 2003 15:04:46 -0700 Thanks Ron and John, I was using the headphone jack and the filter does look flatter using the external speaker jack. I appreciate the help. I had no idea that using the headphone jack could affect things. I checked SSB receive on WWV and the sidebands do sound the same. Guess that's all I can ask for. Thanks again, Todd ++++++++++++++++++