++++++++++++++++++++ See also: K2 KI6WX CW Filter Mod K2_KO0B CW Filter Mod K2 Ki6WX-KO0B CW Filter Mods ++++++++++++++++++++ Date: Thu, 28 Feb 2002 12:52:59 -0800 From: Vic Rosenthal Organization: Transparent Software To: Mark Rozmilowski Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] filtering Mark Rozmilowski wrote: > > I like my K2 very much. However we must be objective. There is a problem with filter "blow by" > when you tune off very strong signal and this takes place on CW and SSB. I consider this a major > problem, > which we should try to eliminate perhaps with help from Eric or Wayne. See for a simple mod reduced leakage around the filter IN MY K2 to a negligible amount. 73, Vic, K2VCO Fresno CA ++++++++++++++++++++++ Date: Thu, 28 Feb 2002 21:42:31 -0800 From: "John Grebenkemper, KI6WX" Subject: Re: [Elecraft] Filtering To: Elecraft Mailing List Mark; Measurements I have done on the K2's Xtal filters indicate that they would have extremely high rejection at 6 kHz away from the received signal. They would certainly be down over 80 dB, and probably over 100 dB. I have also checked the oscillator phase noise and it is good enough that it does not degrade the SSB filter response. The problem is not likely in the K2 unless there is a flaw in the radio. However, on the transmit side, the FCC only requires that spurious signals be down by 40 dB. I would expect that most transmitters 6 kHz away from their transmission frequency will be down more than that. Suppose the transmitter has spurious signals down 60 dB at a 6 kHz offset. If your S9+20 signal follows standard S-units, the spurious signal 6 kHz away will be copied at an S2 level. There is one well known Texas station that runs at least a kW whose spurious output I can hear 50 kHz from his transmission frequency. -John KI6WX ----- Original Message ----- From: "Mark Rozmilowski" > Does anybody know why when you tune K2 away (6 kHz for example) from strong signal 59 +20db and > there are many of those on SSB you can still hear high freq. "noise" from that station. > Is it because filter doesn't attenuate enough or signal is going around the filter. > I would like to eliminate this problem but not by adding audio filtering. This should be eliminated > at its origin. > I think that there is similar problem on CW but I have to do more experiments. > > Thanks and 73! Mark WQ7X > K2 SN#2507 +++++++++++++++++++ Subject: Re: [Elecraft] Filtering To: KI6WX at pacbell.net Cc: elecraft at mailman.qth.net From: "Mark Rozmilowski" Date: Fri, 1 Mar 2002 09:59:19 -0700 John, I agree, K2's xtal filters on CW are as you stated-very high rejection few KHz away from received signal. I was able to confirm that yesterday evening. However, in my K2 I'm hearing signal for few KHz on both sides of center frequency. This signal is bypassing crystal filter. This signal is not very strong but strong enough. I'm very happy that this is not the problem with the cw filter. I have found the solution for this problem and I will publish this hopefully over the weekend. Now my K2 CW filtering works like on FT1000D- no bypassing. If this is just in my radio then is OK with me. Please confirm the following. Insert the signal from the generator or from second radio to the K2 so the S meter shows S +35 to 40db on K2 (I calibrated K2 S meter using my FT1000D as a reference). Put K2 in CW mode, try any filter bandwidth. Tune up and down +/_ 10kHz from the center freq. and let me know the results. Perhaps other owners of K2 could do this experiment and send me email, so if there is no problem than I wouldn't have to waste my time describing the solution that eliminates the "bypassing"issue completely just in my radio SN2507. I HAVE SO MUCH FUN WITH MY K2. Reminds me old days(you know-being very young) when I designed and build my own Transceivers. 73! Mark WQ7X +++++++++++++++++ From: "mark" To: "Elecraft Mailing List" Date: Sat, 2 Mar 2002 18:11:50 -0700 Subject: [Elecraft] K2 CW filter "blow by" solution I have installed the KI6WX modification a week ago.=20 However, I still didn't like the fact that I could hear the signal of = the strong station when I was listening to the week signal a few kHz = away. This probably wouldn't be as noticeable on a very crowded band. My house = is on a hill and I'm using a large 4 el 20 to 10m and a 2el 40m quad = antenna. There are many signals S9 +20db and stronger on K2 or FT1000D S meter. The experiment: K2 CW version only, with W2 and W3 installed. (SSB option not installed) Signal S9 +30db freq 28060.00 Mhz Filter BW 400Hz audible signal from 28056.4 to 28064.0 Mhz almost 8kHz = (that is not the filter response but rather the signal bypassing the = filter). With 700 or 100Hz BW is about the same. The amplitude of the signal beyond the bandpass of the filter is audible = but much lower in amplitude. Next I installed a 1 inch copper tape. With the tape: Same set up as above: Filter 700Hz audible signal from 28058.2 to 28060.0 MHz Filter 400Hz - - - - - - - --- - - - - 28058.7 to 28060.0 MHz Filter 100Hz - - - - - - - - - - - - 28058.9 to 28060.0 MHz NOT BAD 1.1 to 1.8 kHz BW depending on which filter is used. Since I can't place the drawing of my installation, I will try to = describe it; Copper tape L=3D2.1" W 1" Face the front of the K2 One corner of the tape is soldered to the top of X5 left side and the = other corner to the top of X11, in the middle of the can.=20 The right front corner of the tape is cut L 0.65" W 0.5" so that the = tape wouldn't cover the J10. Also, left back corner is cut just enough so TP2 wouldn't be covered. Solder only small area of the tape, 0.1" or so, to X5 and X11. Do not = overheat X5 / X11. I covered the top and bottom of the copper tape with kapton tape so it = wouldn't short anything.=20 In my K2, this mod works very well. Now the cw filters work almost as = well as the filters in the ft1000D. Please try this and let me know how it works in your K2. NOW THE BAD NEWS: THIS MODIFICATION DOESN'T WORK IF SSB MODULE IS INSTALLED. THERE IS A = "BLOW BY" PROBLEM ON CW AND SSB FILTER WHEN SIGNAL IS ROUTED THROUGH SSB = MODULE. IT'S A SHAME, BECAUSE I LIKE THE CW FILTERING AFTER MODIFICATION VERY = MUCH. THE ONLY HOPE IS THAT THERE ARE ENOUGH (CW ONLY) OPERATORS SO THAT THEY = COULD ENJOY THIS IMPROVEMENT. 73! Mark WQ7X=20 ++++++++++++++++++++ From: "Don Brown" To: "Elecraft" Subject: Re: [Elecraft] K2 CW Filter Grounding mod... Date: Wed, 11 Sep 2002 09:17:42 -0500 Hi I have built several K2's and I ground the crystal cans by soldering the = wire to the board then running the wires up both sides close to the can a= nd flowing solder quickly on the side of the can. I solder only one side = of each can, allow them to cool then solder the other side. Any excess wi= re is then clipped flush with the top of the can so as to not interfere w= ith the SSB module. This technique seems to work for me. As was stated in= the original mod description adding the shield wires to the bottom of th= e board and chip bypass capacitors do not really help all that much so I = don't do that part of the mod. The mod does work and it's effect is measurable with Spectrogram so I thi= nk it is worthwhile to do. Elecraft has not approved it probably because = of the possibility of damage to the crystals. If you are careful (and qui= ck) you can do the mod safely. You can always buy another set of crystals= if you screw it up. I have never had a problem with it and I have built = 4 K2's and 3 K1's using the same method. =20 I have seen crystals with grounding wires spot welded to their cans as an= option from the manufacturer. Maybe Elecraft could look into obtaining t= his type of crystal and then we would not have to risk damaging a crystal= by overheating it. =20 All of the other mods should be done after the radio is completed except = this one. It is much easier to do this mod when building the radio than g= oing back and reheating and moving the wires (much safer for the crystals= also) Don Brown KD5NDB ----- Original Message ----- From: Tom HammondN=D8SS Sent: Wednesday, September 11, 2002 8:28 AM To: George, W5YR; elecraft at mailman.qth.net Subject: [Elecraft] K2 CW Filter Grounding mod... Sorry folks, last message carried an INappropriate Subject line. Trying again... _____________________ GM George: At 12:05 AM 9/11/02, you wrote: >Is the delta improvement obtained from grounding at the base instead of = the >top due to the lowered inductance of the shorting wires? And/or their >parasitic capacitance to other circuit components? I cannot knowledgeably answer this. However, I suspect that it it due to =20 the added lead length, which would tend to imply the first of your two =20 choices, above. >Is it acceptable to ground the crystal cases both at the top and the >bottom? If you ground on both sides of the xtal can, as suggested, I don't think =20 there'll be any additional available holes for grounding at the top as we= ll. >Would there be any merit to fashioning some sort of shield can around th= e >filter components? I believe I recall that this has been tried and found to be lacking. >Getting a K2 in a few days and this mod seems to be of such importance t= hat >I want to do it right . . . Were it me, I'd follow the grounding at the bottom recommendations and be= =20 done with it. 73, Tom N0SS ++++++++++++++++++++ From: "Stuart Rohre" To: "Charles Greene" , Subject: Re: [Elecraft] Grounding wire for xtal cans soldering tips Date: Wed, 11 Sep 2002 18:07:07 -0500 With a temperature controlled soldering iron, good sized flat blade tip, and Multicore solder, I found it easy to tin the cans first slightly above the seal, out of harm's way, and then solder the bus wire that had already been soldered in the provided hole on the board. At the frequency of the filter, the length of bus wire thus used will not impair the filter response. Make sure the cans are clean before tinning, to facilitate doing this with minimum heat. I tend to like to use the higher heat setting on my station, and solder more quickly before heat can build up in the can too much. Also, pretin the bus wire end, and you will need minimal heat to join the can and wire. 72, Stuart K5KVH +++++++++++++++++++ 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 +++++++++++++++++