++++++++++++++++++++++++ Date: Sun, 13 May 2001 22:09:13 -0400 From: "Babe" Subject: [Elecraft] CW Filter Rejection Mod. Has anyone tried the mod entitled "Improving The Elecraft K2's CW Filter Ultimate Rejection" by KO0B? http://www.rt66.com/~hypoxic/K2stuff/ultreject.html I'm looking for some feedback, it looks like a useful and faily quick and easy mod. Larry WA2DGD K2 #1672 ++++++++++++++++++++++++++++ Date: Mon, 14 May 2001 10:21:12 -0500 From: "Timothy A. Raymer" Subject: Re: [Elecraft] CW Filter Rejection Mod. Larry, I have discussed the mod with Tom Hammond, N0SS. We are both really intrigued by it, but have not had time to perform it. It definitely would be worth doing and testing. Tim Raymer +++++++++++++++++++++++++++++++++++ Date: Fri, 18 May 2001 09:23:58 -0700 From: "Bob Tellefsen" Subject: [Elecraft] KO0B cw filter mod On Sunday Larry WA2DGD asked if anyone had tried the KO0B filter mod. I hadn't heard of it, so I followed the URL he gave, http://www.rt66.com/~hypoxic/K2stuff/ultreject.html and got the details. In a nutshell, I tried it and it works. You can get the details from the web page. It is easy to do and didn't take very long. For results, my first check was subjective. Before the mod, when I would tune past a signal I could hear it for quite a ways past its frequency. The pitch would be rising and growing fainter, but it hung in for quite a while. Now, when I tune past a signal, I can hear the pitch rise a little bit, then it sort of winks out. After the mod, I took the following measurements to see what was happening. I used the filter peak at 580 Hz with the narrowest setting, 00 bandwidth, for the 0 reference. At 10 db down, bandwidth is 170 Hz. At 20 db down, bandwidth is 210 Hz. At 30 db down, bandwidth is 270 Hz. At 40 db down, bandwidth is 320 Hz. At 50 db down, bandwidth is 390 Hz. At 60 db down, bandwidth is 500 Hz. In addition, the passband curve is more symmetrical than it had been before the mod. After doing the mod, I checked it out with Spectrogram, and could see the improvement in the shape of the response and in the noise in the stop band outside the passband. Try it, I think you will like it. 73, Bob N6WG K2 s/n 12 +++++++++++++++++++++++++++++++++++++++++ Date: Sat, 19 May 2001 09:08:21 -0400 From: Ken Wagner Subject: [Elecraft] KO0B cw filter mod K2ers: I have to admit that I was a bit of a skeptic 'cuz my K2 sounded just fine to me. However, when I read the report from N6WG, I decided to try it. Besides, I have as much or more fun tinkering with stuff as I do operating. It's easy to do if you take reasonable care. It took about 45 minutes from start to finish to do the mods. I do believe that there is an improvement. The quality of the audio was pretty much the same (I had not experienced the "underwater" sound mentioned... all of my sea time was spent on the water, not under it) but the cut off characteristic of the tightened up filter was noticeably improved. Using spectogram, I roughly measured the response (using noise generator source) and got the same results as N6WG reported (within reasonable tolerance). I tried it.... I like it. 73, Ken Wagner K3IU K2 #920 +++++++++++++++++++++++++++++++++++++++ Date: Sun, 20 May 2001 09:46:39 -0600 From: "Santa Fe" Subject: [Elecraft] Re: KO0B CW Filter Mod. ??? The mod calls for a .001 capacitor, which is a 102, but the capacitor is labeled a 103 which is a .01 So which is it??? Fred W5YA / KT5X +++++++++++++++++++++++++++++++++++++++++ Date: Sun, 20 May 2001 18:32:45 -0600 From: "Santa Fe" Subject: [Elecraft] KO0B filter mod Regarding the discrepancy, I used .01 (103) not .001 (102). My results have been gratifying. Before the mod, an S-7 signal trailed off FB as the filters narrowed, but an S-9 signal leaked by. In fact, at .5 khz away from center, regardless of filter width, that signal could be heard albeit weakly. Now, with each filter narrowing, the distance away from center that an S0+ signal can be heard is less, quite a bit less. Spectrogram clearly shows slopes that stay steeper, and stay steep right to near the noise floor. TNX KO0B 72, # 700 ++++++++++++++++++++++++++++++++++++++ Date: Mon, 21 May 2001 23:02:15 -0600 From: Kevin Ferguson Subject: [Elecraft] ko0b thanks filter modders, and ? for Eric. How nice to come home from vacation and find several positive comments about my CW filter mod waiting in my mailbox. Sorry about the confusion on capacitor value (I have just fixed that) Thanks to all for making the time I spent writing up the article worth it. Glad you liked the results. Eric, I would like to link reflector discussion about this mod to the article. I know you don't run qth.net, but perhaps you know if this is the sort of thing they like, or something they frown on?? Please drop me a line. (yeah, I know I didn't ask about linking to elecraft.com....but hey, who's gonna object to free advertising?) - -73- ko0b ++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 21 May 2001 23:10:28 +0000 From: hypoxic at rt66.com Subject: Re: [Elecraft] Radio Shack 0.01uF-filter mod? OK, I am back from a great attitude-adjusting vacation. Sorry to have missed the erlier question vis. correct cap value. Glad to see it was resoloved. I'll be fixing this error in the instructions as soon as I wade through my now very full in-box. > Are the 0.01uF Ceramic Disc Capacitors sold by Radio Shack acceptable > for the KO0B CW filter mod? They are a 20% part. What is the difference > between these caps and the ones that are supplied in with the K2? nearly ANY ceramic disc capaciter should be fine in this application Anything between .1 and .001 will probably be fine. The parasitic resistance and inductance of the capaciter will determine if, and how well it works, not the exact value. Remember, these caps go in paralell with C166. Thier function is to lower the inductance to ground, not to increase the capacitance. Keep the leads short. The value is not at all critical....just don't use an electrolytic. I am not sure the exact cap you are talking about, so can't make comparison to elecraft supplied units....besides I suppose elecraft will occassionally supply various brands etc. depending on availability. - -73- de ko0b +++++++++++++++++++++++++++++++++++++++++ Date: Mon, 21 May 2001 23:34:40 +0000 From: hypoxic at rt66.com Subject: Re: [Elecraft] KO0B cw filter mod > I wonder if something similar would help the SSB filter? Maybe I'll do a > little experimenting... This will almost certainly shift the passband slightly, as any improvement WILL involve altering stray reactances. I know Wayne and Eric have issues with this, as it is very important that the BFO match the filter response correctly in order to keep carrier and opposite sideband suppression up to spec. If there is actual improvement in ultimate rejection, though, both of those numbers should improve. ONLY IF, the BFO is re-aligned to compensate for any shifting of the SSB filter passband. Use spectrogram and carefully note where the SSB XFIL1 skirts fall, both on USB, and LSB. BEFORE any modding, and put them back there_ exactly_ before putting the rig on the air. Mark the filter at some fairly low (-10 dB perhaps) attenuation level, as the goal of such modding will be to change the filter shape at the lower ends of the skirts, so the lower edges should shift inward. One thing I notice on the SSB filter is that some of the xtal cans are grounded in pairs. This gives a very low Z path between those two cans, and a higher Z path to ground. Improvement might be had by breaking the connection between the two cans, and giving the now floating can it's own low Z (short wire) path to ground. Haven't looked into where such connecton might be made. It is REAL tight in there, but I won't say it can't be done. I think it is NOT a good idea to randomly add a bunch of wires tying all the cans togethor. Be aware that shielding can be done wrong and make things worse. Make sure any added shielding has very short path (s) to ground. A piece of foil that is just floating (electrically) will likely have exactly the opposite of the desired effect, because it will serve to link parts of the circuit you need to isolate. - -73- ko0b +++++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 17:53:25 -0400 From: John Subject: [Elecraft] KO0B K2 filter mod, thanks. More or less finished up K2 #2012 yesterday, still need to run it thru Spectrogram. During alignment and test part II, I noticed some filter blow by on 7mhz, kind of like my old pre Sherwood filtered Drake R4C's. I didn't really like it, but what to heck, there weren't many receivers better than an R4C, even without the Sherwoods. I learned to live with the blow by on the R4C until I could afford the Sherwood filters.I figured if the K2 was as good on receive as advertised, a little blow by could be tolerated. (it is slight). Enter the KO0B mod. I wondered if a couple of caps and some wire could make a difference. After reading some posts on the reflector, indicating the mod provided improvement, I contacted Fred, KT5X, exchanged emails with him on the subject. Upon describing his results, he convinced me to do the mod while doing construction part III. When I finished with part III yesterday and fired the K2 up, no more filter blow by, none that I could hear with my old ears. Is the mod worth doing, yes! Have you ever bought Sherwood filters? A couple .01 caps and wire are a lot cheaper. Thanks a ton Fred, for inspiration, and KO0B for a great simple mod. The radio sounds good. So connected #2012 to a 20M antenna, rolled the power up to 5 watts and worked 4Z4DX, first call. Not bad from southern NM. John, K7UP K1#637 K2#2012 ++++++++++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 23:44:54 -0600 From: Kevin Ferguson Subject: [Elecraft] ko0b filter mod article has been revised. The article has been revised to encorporate some things from the list discussion, and also, very importantly, I have added links to the data KT5X supplied me with. The new article is now much shorter too, becuse I took out a lot of my "going off on a tangent" stuff and put it into (linked) sidebar articles. If you are considering this mod, please be sure you check out the latest version now available at: http://www.rt66.com/~hypoxic/K2stuff/ultreject.html Thanks to the list for all your input on this. Hopefully I can stop working on this now...I've got KNOBS to design! - -73- ko0b +++++++++++++++++++++++++++++++++++++++++++++ Date: Sat, 26 May 2001 09:24:22 -0700 (PDT) From: Jeff Burns Subject: [Elecraft] KO0B mod I applied the KO0B mod to my K2 last night, and did not see an improvement. It may have even made things slightly worse. I used 0805 size surface mount 0.001uF chip caps. At first, I used five caps between the various pins. The 0805 chips are just a little bit longer than the distance between pins. After not seeing an improvement I took out all the caps, and raised the cross bar. The bar was a little lower than the recommended 1/16 inch. I was also concerned that the two caps at the ends might be shorting out to the nearby trace. I reapplied only one cap to each end. This time they were above the bar so they could not short to a trace. Even with the change, I saw no improvement. All my before spectrogram pictures were taken around 7140 MHz. After making the modes, I looked at the response at 14047 MHz. At this frequency, the plots look very good. Unfortunately, I do not have a before picture at this frequency. I also made the KSB2 IMD mod at the same time. It should not make any difference. If anyone would like to see my spectrogram plots I can email them directly. Jeff Burns AD9T +++++++++++++++++++++++++++++++++++ Date: Sat, 26 May 2001 16:07:01 -0500 From: "George, W5YR" Subject: Re: [Elecraft] KO0B mod If anyone is really interested in using SpectroGram, I strongly urge them to get the new 6.0.8 release. The demo is still free but it quits after 10 minutes - then it can be rebooted. Registration is only $25 and the program is MUCH better than previous free releases. Same source as always. Remember that you can always measure the actual amplitude of a signal with a scope and then see what Spectrogram gives you - it is a rough calibration but better than nothing. 72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6 Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR, in the 55th year and it just keeps getting better! Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437 Ron D' Eau Claire wrote: > That's my experience with Spectrogram too. It's excellent for showing > relative values, but I can make it do just about anything I want in terms of > 'absolute' level measurements. +++++++++++++++++++++++++++++++++++++++++++ Date: Sat, 26 May 2001 18:06:35 -0600 From: "Santa Fe" Subject: [Elecraft] Re: KO0B; unrelated problem? KO0B is on holiday in Colorado. He will be back Tuesday. Send him your scans and follow this through with him. If I understood Kevin correctly (in conversation this morning while he was visiting), he said you should NOT be able to "see" the filter without a noise source connected to the radio. If you ARE seeing the filter with NOTHING connected to the antenna, I think he is saying you have an internal noise source of some kind (that shouldn't be there and that is greater than filter leakage therefore masking it). He mentioned something about a zener in the second IF. Now, I have seen scans from another radio that had no filter leakage in the before. In that radio, there was no leakage to fix so he experienced no effect from the mod. Anyone who would like to see my before and after scans, e-mail me directly, or they are posted on KO0B's URL. IF your before's look like mine THEN maybe you have reason to consider Kevin's mod ELSE (if your scans look like my afters), the mod is not going to fix a problem that isn't there! 73, Fred # 700 +++++++++++++++++++++++++++++++++++ Date: Sat, 26 May 2001 18:52:52 -0700 (PDT) From: Jeff Burns Subject: RE: [Elecraft] Ko0B mod - unrelated problem? The band dependent behavior I observed was due to the pre-amp. On 160m and 40m it was turned off. On all the other bands, the pre-amp was on. The pre-amp seams to be a good noise source. With an antenna attached, the filter response looks much better with the pre-amp on. I do not understand why this is. The noise I see with the pre-amp off is more than what comes from the audio stages. So the pre-amp is not just busting the IF noise enough to mask noise from later stages. Does anyone have an idea what is happening? KT5X was your pre-amp on when you made the plots that are posted on Ko0B's web page? AD9T - --- Ron D' Eau Claire wrote: > Jeff, AD9T asked: > >When I reported that the Ko0B mod had not improved my filter > > performance someone suggested that I try running spectrogram > without an > > antenna attached. I just did that, and found the results > interesting. > > > > The results on 160m, and 40m band were different than all the other > > bands. On every other band the noise was shaped as I would expect > by > > the filter. On 160m and 40m the noise was relatively uniform across > the > > audio spectrum - drooping off at the higher frequencies some. The > > noise level was also noticeably less - according to spectrogram 8 > to 10 > > dB less. > > Interesting that it would vary according to the band. Were you sure > that the > setup was the same on all bands (preamp off, same filter, etc.)? > > My Spectrogram shows the computer noise floor (no plug in from the > radio) at > about -60 dB. Connecting the radio with the r-f gain at minimum and > running > up the audio to full gain brings the noise up to about - 50 dB at the > peak > (around 500 Hz) with a gradual roll off with frequency. That's what > I'd > expect in high frequency roll-off from the audio channel. Nothing > should be > coming through the i-f and filters at that point. > > Turning up the "r-f" gain (actually it's adjusting the gain of the > i-f > stages in the K2) brings up the noise to about -20 dB with the audio > still > wide open. Mind you, that level will vary according to how 'hot' your > audio > amp is in the K2, and previous posts suggested that they very a GREAT > deal! > My K2 usually has an attenuator plugged into the headphone jack > because > otherwise I am running the audio gain control down against the > minimum stop > all the time to keep from breaking my ears. Elecraft has suggested > that ops > put some resistors in place of the jumpers for the AF filter board to > cut > the gain on many K2's. So the audio channel noise contribution is > usually > pretty slight. Running the audio gain at a "normal" listening level, > having > no antenna and the r-f gain full up (AGC off) puts the noise at just > a > little below -50 dB. > > At all times it is quite flat, trailing off as the frequency > increases. It > is important to be sure the preamp is off, though. It produces > visible noise > in the filter passband even without an antenna. > > To be fair when checking any rig this way, there should be a dummy > load on > the antenna to properly terminate the receiver front end, although it > does > not seem to be required on the K2 (nice stable design). > > If that's not a typical response, I'd like to know. K0OB also > suggested to > me that my second i-f filter (responsible for reducing the broadband > noise > at the i-f output) might be malfunctioning, allowing too much noise > to slip > through and masking the improvement his mod is supposed to provide. > > Ron AC7AC > K2 # 1289 ++++++++++++++++++++++++++++++++ Date: Sat, 26 May 2001 13:33:08 -0700 From: Phil Wheeler Subject: Re: [Elecraft] KO0B mod Jeff Burns wrote: > > I applied the KO0B mod to my K2 last night, and did not see an > improvement. It may have even made things slightly worse. I've not tried that. > I also made the KSB2 IMD mod at the same time. It should not make any > difference. > The IMD mod did make a huge difference in the IMD reports I receive with the K2 on PSK31 (assuming that's what you are referring to). Phil W7OX ++++++++++++++++++++++++++++++++++ Date: Sun, 27 May 2001 09:12:30 EDT From: WA9GQT at aol.com Subject: [Elecraft] K0OB CW Mod Hi All! Just wanted to let you know that I performed the K0OB cw mod on my K2 after installing the 2nd X Fil Mod. I am very pleased with both of these modifications. I noticed definite improvement with the cw mod; no more sonar type sound. I have never used spectrogram; strictly tune filters by ear or by the book(cw). After doing the cw mod, I set all filters for cw & cwn per manual. Like I said I could definitely tell a difference. I have used the K2 on cw during CQ WW WPX contest and seems to perform quite well. By the way; I used 0.01 uf capacitors from Radio Shack-RS 272-1065 & followed Kevin's procedure to the "T". Thanks again Kevin. 73, Rod WA9GQT K2 #1900 ++++++++++++++++++++++++++++++++++++++ Date: Mon, 28 May 2001 07:18:22 -0600 From: "Santa Fe" Subject: Re: [Elecraft] Noisy K2. Boy... mine is NOTHING like that! > Clearly, when picking "nits" in the K2, different rigs are quite different! > > I use CW filters at 1100 Hz, 600 Hz and 100 Hz bandwidths. The 600 Hz filter > is virtually identical to the 1100 Hz filter, and the 100 Hz filter is no > more than 3 dB down from the 600 Hz filter The OPT1 is about 2 dB below the > 1100 Hz filter, at least at the sidetone frequency. > > Ron AC7AC > K2 # 1289 It WAS, though, before Kevin's mod. Let's see. For CW, now, I originally set the widest at 1.2 kHz. Never liked the way it sounded. Eventually I realized that at that width there was a double bumped peak. I fussed while watching it on Spectrogram and observed that at about 1.0 the peak rounded up and was symmetrical, so settled on that. Then I chose 600, 300, and now for the narrow one. I noticed that any narrower than 50, the slopes overlapped, and that was when I began to lose sensitivity in the narrow filter, so settled on 50, not zero as some have done. Before Kevin's mod to clean up blow-by, I could hear a loud signal on up the band the same distance from center no matter which filter I used, just like you say. After the mod, however, now such signals disappear progressively sooner and very soon indeed in the narrow filter. I used spectrogram on my MP INRAD filters. Those filters are, without a doubt, steeper skirted. The 250 cycle INRAD has the same width at the bottom of its slopes as the K2 variable filter set at 50 cycles has! At -6 db, however, the K2 filter is more narrow. With the filter blow-by cured, what I am telling you is that the K2 filter is over-all more narrow than the INRAD 250 cycle filter. (Lest one forget, the MP can throw in a 50 cycle DSP filter that is, uhhh, shall we say, STEEP!) Also, I neither hear nor see any difference in sensitivity between any of the filters, inclduing OPT1. Rarely operate SSB, but when I do, I do not bother with any of the variable filters as their varied peaks are not good to work with. Speaking of OPT1... How wide is it? It sounds 2.4. I wonder what is involved making it, say 2.2 ??? 73, FD # 700 ++++++++++++++++++++++++++++++++++++ Date: Mon, 28 May 2001 11:05:16 -0400 From: Ken Wagner Subject: [Elecraft] NO0B Filter Mod K2ers: In an earlier post I said that I had tried the mod and I liked it. However, I only had Spectrogram images from "after" the mod. AG1L let me use his K2 (s/n 917) for some "before" info and then I modified the 917 and got "after" data. The images from Spectrogram were disappointing. They showed virtually no change in the response of the filter. However, my ears seemed to perceive a difference. So, I tried something different. Using my TR7 into a dummy load to generate a test signal, I carefully tuned the K2 up and down from the filter center(600 hz) and measured the level and frequency using Spectrogram. The results in the blow-by area are remarkable. Before the mod, I could still see the test signal at 7500 hz. It was 'way down there, but I could see it. After the mod, the test signal disappeared at around 4500 hz. For those interested, navigate to this URL to look at the images and get more info on how I did it. http://users.ids.net/~kewagner/917/ 73, Ken Wagner K3IU ++++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 28 May 2001 12:29:13 -0700 From: "N7SG K7FD" Subject: [Elecraft] Bye bye Blow-by? OK, I just finished up Ko0B's K2 filter mod and I'll give it a thumbs up, if only that it sounds better to my ears. I haven't looked at it with Spectrogram, and I'll leave that to the computer guru's to decipher. Wish I'd done the mod before the WPX...not many strong signals on the band today to 'field' test it with... 73 John K7FD Ko0B mod http://www.rt66.com/~hypoxic/K2stuff/ultreject.html +++++++++++++++++++++++++++++++++++++++ Date: Mon, 28 May 2001 19:29:29 -0700 From: "John Grebenkemper, KI6WX" Subject: [Elecraft] Setting Audio Levels in Spectrogram Recently a number of folks on the reflector have been using Spectrogram to make measurements of the K2's filter response. If the audio input level is set too high, clipping will occur in the sound card which will create intermodulation distortion and incorrect readings from Spectrogram. This problem is particularly apparent when measuring broadband noise which is done when making filter response measurements of the K2 filters. For making filter measurements, Spectrogram should be set to 11K Sampling Rate, 16 bit, Mono, and 512 FFT. You can set the other parameters where you want, but I would recommend using the 90 dB dynamic range since it will provide valid measurements as long as you don't overdrive the audio input. For some reason, v6.0.9 displays levels that are 10 dB less than v5.1.6 for the same audio input signal. All measurements given below are for v5; v6 users should set the following guidelines 10 dB lower. When making measurements with the SSB filter, intermodulation distortion will occur when the noise level exceeds -35 dB on the Spectrogram scale.. To leave some headroom, I would recommend taking these measurements with a maximum level of -40 dB. The narrower CW filters with a bandwidth <1kHz provide less noise power so one can measure to higher levels without clipping. These filters start to show intermodulation distortion when the Spectrogram level exceeds -30 dB. Again to provide some headroom, the audio level should be set so that the narrow CW filters do not exceed -35 dB in Spectrogram. A pure tone can be measured to somewhat higher levels in Spectrogram. One measurement I made showed that an over the air carrier received by the K2 started to show intermodulation distortion when the level approached -20 dB on the Spectrogram scale. Any sort of complex modulation would show intermodulation distortion at lower levels. To be absolutely safe, the Spectrogram levels for noise can be followed and you will be guaranteed not to have intermodulation distortion problems in the Spectrogram measurements. In summary, if you use Spectrogram to make K2 filter measurements, make sure that the displayed signal level in Spectrogram does not exceed -35 dB (-45 dB for version 6) for filter bandwidths less than 1 kHz and -40 dB (-50 dB for version 6) for bandwidths wider than 1 kHz. - -John KI6WX ++++++++++++++++++++++++++++++++++++++ Date: Wed, 30 May 2001 07:39:46 -0400 From: Ken Wagner Subject: [Elecraft] Ko0B Filter Mod (My Last Posting) K2ers: After swapping a couple of emails with John, KI6WX, and reading his "tutorial" on Spectrogram(Thanks, John, I needed that!), I decided that I needed to do some more work on the before/after measurements that I reported the other day. Actually... only the AFTER measurements got redone (I'm not gonna undo the mod). The results still show a marked improvement but not nearly as dramatic as previously indicated. The web page has been updated... http://users.ids.net/~kewagner/917/ This is far as I'm gonna take this. It's been fun, but I gotta find something else to play with... xyl suggested the lawn mower. 73, Ken K3IU K2 #920 +++++++++++++++++++++++++++++++++++++++++ Date: Wed, 30 May 2001 21:22:53 -0600 From: Kevin Ferguson Subject: [Elecraft] Sigh...anotherk2 cw filter mod update. It has become clear that that the mod doesn't work for everyone/everyrig. I have updated the article to reflect this, and linked in a compendium of postings where there was no improvement. I wish I knew why some hams are not benifitting from this....but feel it is important to present all sides regardless. - -73- ko0b http://www.rt66.com/~hypoxic/K2stuff/ultreject.html +++++++++++++++++++++++++++++++++++++ Date: Thu, 31 May 2001 06:56:05 -0600 From: "Santa Fe" Subject: [Elecraft] Re: cw filter mod observations For what it is worth, here is what I think I have observed: I have seen scans from a handful of radios that I think I can put in three categories... 1) Radios with before scans that suggest there is already little filter blow-by. These builders when questioned have said to me they elected to use very short ground leads on filter crystals at the risk of possible damage to the crystal. These radios did not benefit from the mod. This suggests that the majority of benefit MAY be from the second ground lead. 2) Radios with before scans that suggest there may be noise getting past the crystals at less than 30 db down from the peak. If there is benefit from the mod in these radios, it may be masked. These radios reported no improvement from the mod. 3) Radios with before scans showing noise creeping into the slope of the filter down close to the noise floor. Radios like this seem to benefit from the mod. I am NOT an engineer, and I have made scans only on my own radio. Spectrogram settings and noise sources vary making data from different people hard to accurately correlate. Several knowledgeable contributors have suggested the K2 AGC and gain settings can contribute to inconsistent scans from one radio to the next. All these things make analysis just a tad unscientific. The one thing I can say for sure... the mod helped my radio and I sure appreciate Kev's contribution! 73, Fred # 700 > It has become clear that that the mod doesn't work for everyone/everyrig. > > -73- > ko0b > > http://www.rt66.com/~hypoxic/K2stuff/ultreject.html ++++++++++++++++++++++++++++++++++++ Date: Thu, 31 May 2001 19:40:44 -0700 (PDT) From: Jeff Burns Subject: [Elecraft] Ko0B CW Filter & Spectrogram Previously when I reported that I had not seen any improvement with the Ko0B CW Filter mod I was basing that on Spectrogram output - not on listening. Others comments made me suspicious that my measurement methods were at fault. I have improved my measurement methods and now suspect that any improvement was masked by noise in the audio setup. Without removing the mod I cannot verify that any improvement was made. Perhaps someone else can make better before and after measurements. The biggest problem I had was an audio amplifier between the K2 and the computer sound card. It was generating significant noise. Removing it made a significant improvement. To make my final measurements I made a N0SS type noise generator. I included an attenuation pot on the output of the noise generator. The ACG was turned to off, and the pre-amp to on. I repeated the measurements at three different audio gain levels. At each AF gain level I adjusted the pot on the noise generator so that the peak signal read -15dB in Spectrogram. I found that as the audio gain was increased the noise floor raised considerably. With the AF Gain at max the noise was greater than -60dB. This is enough to make the "Good" plots that others have reported look "Bad." I suspect that the differences that people see are related to the amount of audio gain in the measurement setup. Even with high audio derived noise levels the RF section may be attenuating off the air signals that previously made it through. This could explain why it sounds better, but sometimes does not look better in Spectrogram. Jeff Burns AD9T +++++++++++++++++++++++++++++++++++++++++++++++ Date: Thu, 07 Jun 2001 07:16:45 -0700 From: Louis Hlousek Subject: Re: [Elecraft] Mod to K2 CW Filter To Improve Rejection >From what I understand the danger in soldering the crystals near their bases is the possibility of damaging the can seal. I don't know how easy it is to damage the xtals with heat but using low temp indium solder might be a way to avoid potential damage. Alloys are available with melting temperatures raging from below room temp to over 250 C. Indium Corp is one manufacture. www.indium.com/ . I used this stuff in graduate school to solder directly to metalized piezoelectric materials. I don't know how readily available this stuff is in small quantities but it might be useful for soldering the grounding leads to the xtal cans if they can indeed be easily damaged by normal soldering temps. Anybody else have experience with low temp solders? Lou W7DZN +++++++++++++++++++++++++++++++++++++++++++++++ Date: Thu, 07 Jun 2001 07:25:29 -0700 From: Wayne Burdick Subject: [Elecraft] KO0B/KI6WX mod to K2 CW filter I wanted to thank John for doing such a comprehensive job in updating KO0B's original mods. The plots show the mod to be working well, and the extra insertion loss is not likely to be an issue for most ops. John will be visiting me this weekend so we can compare the KO0B/KI6WX crystal filter mod to the N6KR audio filter ;) In case you didn't recognize his call or name, John is the designer of the "Tandem Match," an accurate directional wattmeter, that has been featured in the ARRL Handbook. In the 1996 Handbook it can be found on page 22.36. 73, Wayne N6KR "John Grebenkemper, KI6WX" wrote: > > A month or two ago, KO0B sent out a modification to the CW filter that > improved its sound quality, but there were no measurements... > > One thing led to another, and I have come up with a somewhat different > modification... +++++++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 13 Jun 2001 08:19:18 -0600 From: Kevin Ferguson Subject: [Elecraft] (K2) Insertion loss and CW filter mod. At first I was puzzled at the increased insertion loss John Grebenkemper (KI6WX) measured after modifications to improve the ultimate rejection. The text of John's write-up indicated that he had accurate instrumentation, and (more importantly) the skill and experience to make valid 100+dB dynamic range measurements....I did not doubt the accuracy of his insertion loss measurements: as I said: Puzzling. I think I have worked out why this is so. Now even though this is based on a lot of experience and knowledge, fits all the observations, and relies only on conventional electronic principles, it is still SPECULATION, and I can't prove it.... See, I know this....there is no need to remind me of it. Note that it is just this sort of gedenken experiment that lead me to start tweaking on the filters in the first place, and a lot (not all of course) of K2 lovers seem to think that was a good thing. Consider the path that out-of-band signals which leak around the filter must take: 1) Some signal couples to the case of X7 from it's input electrode. 2) This signal is partly shorted to ground by xtal grounding wire(s), but some of it still survives, coupling to output electrode of X7, and also to case of X8. It is here that improvements to ultimate rejection are accomplished. Reducing the inductance of the case-to-ground connections strongly attenuates the signal level on the cases. and reduces the efficiency of between-case coupling. 3)Most of what couples back into the (intended) signal path gets attenuated by successive crystals X8-X11. Also, because the signal does not match the crystals resonant frequency, such coupling is fairly weak. 4) This coupling continues in a like fashion down the line, though any signal coupled back into the intended path experiences successively less attenuation, as it must pass through fewer rocks on it's way to the output. 5) Finally, at X11 there are no additional crystals to attenuate whatever might leak back into the signal path...What survives is "blow-by". In a "stock" K2 this is at about - -45dB, or 1/10 of a percent of the in-band voltage present at the output. (based on specrograms of several unmodified K2's) In-band (or GOOD) signals experience the same "leakage path", except that in step 3, the coupling is much more efficient, and any signal that makes it's way back onto the intended signal path early gets a nearly free-ride to the output. However, the improvement in grounding mentioned in step 2 does not distinguish between desired and out-of-band signals! My thesis, then, is that the leakage path for in-band signals is much more efficient than it is for out-of-band stuff. (nearly as efficient as the intended signal path, if I am interpreting John's data correctly) This leakage lowers the insertion loss of the filter. When the leakage of the filter is essentially eliminated, the insertion loss increases to it's "real" value. Now don't misunderstand me...This leaked signal is just as good as what passed through _all_ the rocks, but I'm willing to give it up in order to hear signals "fade-to-nothing" as I tune across the band. Anyway, that's how I see it - -73- ko0b +++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Sat, 15 Sep 2001 13:02:55 -1000 From: John Buck Subject: [Elecraft] KAF2 comments and Test of CW Filter Rejection Mod. per KO0B/KI8WX Finished the KAF2. It tuned as advertised and really does a good job eliminating residual noise outside the desired passband. This filter is a must have for both CW and SSB modes. The listeners noise fatigue is greatly reduced. While I had the system open I decided to incorporate the KO0B/KI8WX shielding suggestions to improve the basic CW filter. K2 #1242 has all currently available options and significant mods, such as XFIL, Sine sidetone and PSK 31 installed. I made the best measurements I could using Spectrogram 6.2.3 The measurement system had a 70db below signal capability using the 90 db range. No Spectrogram or receiver setting changes (except for filter selection) were made during the modification and test process. I used a broadband noise generator as the signal source. Careful measurements were made three times: 1. Before modification; 2. After the crystal ground wires were modified by soldering to the side of the cans; 3. After the addition of the .1uf surface mount capacitors per KI6WX with the Gull Wing shield wires per KO0B. I printed the Display plots for each of the 3 measurements for each of the four filter settings. OP1, 700Hz, 400Hz and 100Hz. FL2, 3, and 4 are centered on 750Hz sidetone choice. When the plots were overlayed using a light box so I could see any differences, the following the conclusions were reached. A. There was no harm of any type due the the changes. I did not see any evidence of the slight broadening of the top of the filter response curve reported by one of the authors. In all cases, each sucessive plot coincided with or fit within the previous plot. B. As expected, the FL1 OP1 filter showed no significant changes. (KSB2 installed) C. The FL2 700 Hz filter shows 2 to 3 db improvement in the 1500 to 2000Hz area. Almost all of the improvement is from the crystal can grounding change. No effect from the gull wing and capacitor additions is seen. D. The FL3 400 Hz filter also shows 2 to 3 db improvement in the 2000Hz area with noticable improvement starting in the 1000Hz region. The gull wing plot is almost identical to the grounding plot but there is a db or so in the 2000Hz area. E. The FL4 100 Hz filter shows about 5 db in the 1800/2000Hz region. About 2 db is due to the gull wing mod. About 1 db overall improvement starts as close as 1000 Hz. Was it worth it? Probably. My K2 now has even better close in rejection of strong signals than before. Knocking down a signal 400 Hz above the center of my filter by another db or two or a signal 1000 Hz higher by 5db could make a real difference. Then I can turn on the KAF2 audio filter for even more help! Who said that K2 does not have bells and whistles? I have .jpg files of the plots on my system if someone really wants to analyze my data. I did not make the .txt spreadsheet readable files however. I freshly downloaded Spectrogram for this effort and did not discover that feature until I was almost done. Aloha, John KH7T ++++++++++++++++ From: "Ferguson, Kevin" To: "'elecraft at mailman.qth.net'" Date: Wed, 11 Sep 2002 17:41:17 -0600 Subject: [Elecraft] re: K2 crystal grounding and blowby. Well, the subject has come up again. As the guilty party that got this whole thing started, allow me to give the history of the mod: My previous rig was a TS-520 that leaked IF through the SSB filter when the CW filter was selected...after fixing that, I felt the K2 was suffering from a similar problem, and set about to see if I could fix it. When I came up with the mod, my idea was to improve the inter-crystal sheilding as much as I could easilly do. I did this by adding a few wires to the board, and using the second set of grounding pads, and adding a second ground wire to the top of the crystal cans, wrapping the ground leads so that the wires would not mechanically interfere with the SSB option board. I also added some additional bypass capaciters to the variactor bias resistor network, and some grounded wires laying on the underside of the board. These changes made a notable improvement to the filters ultimate rejection, as tested by my ears. I was delighted with the result and wrote up the mod for others to enjoy. Then all heck broke loose. Some hams tried the mod and noted a similar improvement....notably Fred, KT5X, an accomplished contester. He made measurments using spectrogram that confirmed his and my own "by ear" estimates of the improvement. I compared the improvement to the difference between good NR analog tape, and CD audio. The tape can be really good, but the CD will be notably better. Fred is an FT-1000 MP owner, and his rig is equipped with inrad filters. He has compared the performance of the modified K2 filter, and was impressed. Spectrogram revealed that the inrad filters have a slightly better shape factor as I recall...However the modified K2 gives a lower noise floor...and of course the K2 does not offer the option of adding DSP filtering to that provided by the IF filters. So why all the fury?...well, some hams noticed NO improvement. And a huge debate insued. In at least one case, (possibly John KI6WX ??) it turned out that the builder had grounded the base of the crystals when the rig was built. Also note that this mod improves the filter performance at a point where it is already providing about 35-40 dB of attenuation. You aren't going to hear a difference if there is a passband signal that is pulling the AGC down by that much, and you may well not hear a difference if you don't have good hearing. If you have less than 40 dB of dynamic range left outside the CW passbands, you CAN'T possibly detect the improvement. Stock, _I_ can hear ~S7 or stronger signals on the opposite side of zero. (other sideband) Modified _I_ can't. Unmodified, I can tune through strong signals and still hear them up to the frequency limitations of my hearing. Modified the amplitude fades to undetectability long before a frequency limitation is detected. Furthermore, when measuring with spectrogram, it is easy to overdrive your sound card, causing distortion products which will mask any improvement. Enter John, KI6WX who has access to some excellent test equipment. His measurements indicated that, up to the limits of his equipment, (~100 dB IIRC) ALL the improvement was due to improved crystal grounding, and grounding the crystals at the base yielded superiour blowby performance. My rig currently has all the CW filter crystals grounded on both sides at thier bases, using short leads. In addition, I shortened the ground leads on the 2nd IF filter, as well as the SSB filter on the option board. The wider filters do NOT allow the blowby to be as easilly heard as the narrow CW filter, however, I figure every little bit helps. I have not removed the capacitors nor the shield wires. It has been mis-stated that these were shown to be ineffective. A correct statement would be that no improvement could be measured. An equally correct statement would be that no degradation could be measured. For those who doubt the efficacy of improved crystal grounding: It is a FACT that ultimate rejection is NOT established by the "intended" circuit design. You can't analyze the circuit schematic and predect what it will be. It is all in the physical implimentation. Parasitic terms, and stray coupling are the culprits. Of course some really industrious soul might be able to model this. Not me. So how does the mod improve ultimate rejection? Can't prove any of this, but here is what my experience tells me: My thinking was that doubling up the ground wires should halve the reactance between the cans and ground...thus yealding a ~6 dB reduction in blowby at each crystal. Don't know if I was correct on the reason behind it, but the expected improvement was (is) real. Another VERY effective way to reduce inductance is by shortening the wires. Grounding the crystals at the base reduces the lead length by much more than half. Adding a second such wire gives a further halving. It should be possible to reduce the inductance between the crystal case and ground to about 1/10 that provided by the instructions. That should result in about 100 dB reduction in the coupling between the cans. Does this improve ultimate rejection by 100 dB? NO! there are other ways signal can sneak past the filter. As you plug the big leaks, the smaller ones contribute a greater share. Also, 100 dB is about the dynamic range limit of good test equipment. Improvement beyond that point won't be measureable. Human hearing has similar limitations...so you probably can't hear any difference between 100 and 120dB ultimate attenuation. Also, I have finally figued out one thing that at first puzzled Fred and myself. On both CW and rev CW the mod improved the low frequency skirt more than the high frequency skirt, as measured using spectrogram. The reason is that the blow-by allows the noise from the opposite sideband to alias into the lower skirt more than the upper skirt, so there is more improvement to be had on that skirt than on the high frequency side. This is becuase the outer skirts still fall off at ~6dB/decade without the mod. (modified they are at around 30 dB/decade, continuing the slope of the intended response) -73- ko0b +++++++++++++++++