++++++++++++++++++++++++++++++++++++++++++++++++++++++ Fred; The first time I tried to dip C55, the dip was beyond the minimum value of the capacitor. I re-did the one turn loop in T1 by increasing its length by 1/4" so that the loop was at least 1/8" away from the core. This reduced the stray capacitance and I was able to get a two dips on either side of the minimum capacitance. If you still can't get it to the minimum dip, you can adjust R3 or C54 slightly and it should dip. You can compute the approximate null values with the following equation: C55/(C55 + C54) = R3/(200 N) where: C55, C54, R3 are the values of the parts in pF and ohms N is the number of turns on the secondary of T1 (N=10 in the current design) > > 1) When trying to dip C-55 the lowest I can achieve is about 025 and this > occurs with the slot vertical, or at right angle to the panel, such that I > think the null is beyond the range of C-55. I think that I am not the first > to experience this. What is the solution? This could indicate a problem in the circuitry associate with T1. Are both R1 and R2 turned fully clockwise? Do you have the right number of turns in T1 and are the right values in R3, R4, and C54? You should also measure the same transmit voltage at pin 3 of U4. > > 2) The ERRATA sheet following page 16 says the rcv voltage on pin one of > LM-358 should be zero, and it is. It then states that the voltage on pin > one during five watt transmit should be between 3 and 4 volts, but I am > reading 1.7 volts. Is this a problem? - -John KI6WX +++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Marinos: > > >When adjusting my ATU's C55 in the CALn mode and with a 50 ohm > dummy load > >connected in the 40m band (as suggested by the manual), I can not > achieve > >a value lower than 0.04. > > First, some of the tiny tuning capacitors have been found to work > best if > they are rotated through a full 360 degrees of rotation SEVERAL > TIMES > before you actually attempt to 'tune' with them. If this does not > solve > your problem, then... > I had the same problem with that tuning capacitor. After I tooke the capacitor out, I found the axle of the capacitor not well connected to the movable plate. So, when turning the axle, the plate turned only after turning the axle about 30 degrees and the contact between axle and plate was poor. A drop of solder cured the problem completely. P. Gerber HB9BNI ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 14 Nov 2000 06:38:16 -0600 From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] C55 null point question Marinos: >When adjusting my ATU's C55 in the CALn mode and with a 50 ohm dummy load >connected in the 40m band (as suggested by the manual), I can not achieve >a value lower than 0.04. First, some of the tiny tuning capacitors have been found to work best if they are rotated through a full 360 degrees of rotation SEVERAL TIMES before you actually attempt to 'tune' with them. If this does not solve your problem, then... Depending upon whether you have made the C50/C51 mod (changing the .01uF caps to .001uf), or whether this mod may have already been included IN your release of the KAT2, obtaining .04 may be a GOOD thing. If you still have .01uF caps at C50 & C51 in your KAT2, then .04 may be a bit high, and may not represent the bottom of the null. In this case, you may want to try using an ANALOG voltmeter connected between GND and the high side of the REFL pot to give you a more easily read indication of the null. Trying to adjust for a minimum reading while using a digital meter can be somewhat difficult due to the fact that you may have passed through the null while the meter was counting. Using an analog meter should allow you to readily find the real null point. Now, IF your model of the KAT2 already HAS .001uF caps installed at C50/C51, then obtaining a .04 reading is quite a bit better than most users have been able to obtain... usually something in the .08-.11 range is more normal. IF your KAT2 still has .01uF caps in it, then you should strongly consider changing them to .001uF caps. This change, while NOT significantly effecting the operation of the WATTMETER/SWR bridge, WILL significantly benefit the SSB option when/if it is installed, but allowing the ALC to operate properly when is SSB mode. The time constant of the .01uF caps was found to be too long, thus not allowing the ALC to recover properly when in SSB mode. >The ATU seems to work OK in all bands with my 19m log wire antenna, except >that in the 10m band it can only bring the SWR to 1.7/1. And, in truth, the ATU may not be able to achieve an SWR better than 1.7:1 on 10M with that particular antenna. You may wish to try using the alternate (ALT) tuning algorithm, which may be selected from the ATU selection from within the MENU system. Although this algorithm was designed more specifically for use with very short antennas (e.g. whips, etc.) you may find that it does a better job on tuning 'problem' antenna situations. If this still does not solve the problem, you may wish to consider adding or removing a few feet of wire the to total length of the existing wire. This may change the 'characteristics' of the antenna enough that the AUTO algorithm may be able to better tune tune the antenna on that particular band without materially effecting the tuning on the other bands. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ In a message dated 09/03/2000 10:18:54 Central Daylight Time, wb8icn1 at juno.com writes: << 2. My POUT for both forward and reverse are always the same. >> This normally indicates that there is an open circuit between the K2 and the dummy load. This can be caused by several reasons. The easiest one is that you have the dummy load connected to antenna 1 and the KAT2 set for Antenna 2 or vise versa. A quick check I used was to remove the LC circuit board and place a jumper between Pin 3 of J4 and Pin 14 of J5 on the Control board, Then attempt the null operation. If it works properly then the control board is ok and you have isolated the problem to the LC board. If you still have problems it probably is a problem with T-1. I have found it much easier to adjust C55 by using an analog voltmeter set to the lowest range (2 Volt) and monitor the voltage between ground and Pin 4 of U1. You can then adjust C55 very easily watching the analog meter. The digital meter in the K2 has some delay in its response. If the problem is indeed on the LC board do a visual inspection of the relays to make sure they are all installed properly. I just repaired a KAT2 that had one of the relays installed backwards and it exhibited the very same indications you are describing wiht yours. It is very easy to check as all the relays should have the wide line on the end of the relay pointing to the outer edge of the LC circuit board. If this doesn't help you please fel free to call me at 334-633-8581 and maybe I can tell you other things to try. good Luck and 72/73 Jim Younce K4ZM K2 SN:18, 1117, 1527 & 1555 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Notes on setting up the FWD/REF Power settings on the KAT2 ATU AB7MY When doing the Reflected Power null adjustment on C55, you may find it difficult to determine when you reach the null of the trimmer cap by relying solely on the K2's Front Panel LCD display. Even at low settings of the Power control, it is common to get a Hi reading on the display when first adjusting C55. Preset C55 to its mid position, with the screwdriver slot parallel to the wide portion of the KAT2 Control Board. First be sure you have the proper 50 dummy load connected to the ANT1 connector of the KAT2, and that ANT1 is the selected antenna jack on the rear of the K2's top cover when the KAT2 is installed. See page 16 of the KAT2 manual. Set the K2 for the 40m band. Be sure the Power setting is set for low output, below 1 watt to start with. Since it is easy to miss a dip in the null of C55 when a digital display of the Reflected power is used, you may find it easier to connect an analog voltmeter to the ungrounded side of trimmer pot R2 on the KAT2 Control PCB. This is the terminal of pot R2 nearest to C55. Set the analog meter to read about 3-5 volts full scale, and press the Tune button on the K2. Slowly adjust C55 with an insulated tool for a dip in the meter reading. Once you get close to the null, you may see the digital display on the K2's Front Panel indicate a small value of Reflected power. Gently turn C55 until you obtain the lowest reading on the LCD. It should be zero, or very close to zero. You may then want to increase the K2's Power control to 5 watts or so, to verify you have achieved a good null. Making the preliminary adjustment at a lower power level may make it easier to get close to the null setting, and then the final adjustment to C55 can be done at 5 watts. WARNING: DO NOT SET THE K2's POWER CONTROL TO MAXIMUM UNTIL YOU ARE SUCCESSFUL IN ACHIEVING A NULL IN THE SWR SENSOR! It is possible to damage the contacts of the latching relays in either the K2's low-pass filter, or one of the relays in the KAT2 if there is a short circuit from the RF path to ground. High RF currents can damage the relay contacts if there is a short circuit. Heed this warning to prevent costly relay damage and subsequent replacement of a failed relay. If this procedure does not work, and you cannot get a null on C55, then check the SWR sensor T1, and all of the components in that portion of the schematic. Be sure you have a good 50 ohm dummy load connected to the KAT2, and that the proper antenna connector (ANT1) is selected using the Tap ANT 1/2 feature of the Tune button. Examine the interconnecting cable and connections to the K2's Control PCB if there is no indication of Reflected or Forward power at all to the K2 display from the KAT2 SWR sensor. You can use an ohm meter to verify continuity between the RF input cable of the KAT2, and each of the antenna connectors on the KAT2 when either ANT1 or ANT2 is selected, since all of the inductors (and capacitors) are switched out of the LC network when in CALn mode. Also, there should be no continuity to ground anywhere in the RF path of the KAT2 with it disconnected from the K2 RF connector, from the RF input cable or either antenna connector. Any fault in these connections will prevent the CALn adjustment from nulling. Note that there *is* a DC short to ground in the K2's RF output circuitry, because of the 3-4 winding of PA output transformer T4. Do not be fooled by this when checking the KAT2 RF path for shorts and opens. Disconnect the RG-174/u cable from the K2 and remove the 50 ohm dumy load if performing continuity tests on the KAT2 RF path. After the CALn procedure is completed, continue in the manual to set the Power calibration and trimmers R1 and R2 to their proper settings, as shown on page 17 of the KAT2 manual. This information should help speed the alignment of the KAT2, and assist you in troubleshooting if there is a problem. As always, your feedback is welcome. ++++++++++++++++++++++++++++++++++++++++++++++++ From: "Alva Anderson W5VCJ" To: "Vic Winton" , Subject: Re: [Elecraft] KAT 2 C55 null Query Date: Fri, 8 Feb 2002 08:37:29 -0600 Vic, I had the same problem, and the readings were unstable anyway. If I tried to get closer, they seemed to vary wildly. Try turning down the power to 1W to do the null adj. Then things will get much easier. BTW, others have said that 009-011 or so worked just fine for them. Andy W5VCJ > > I can only achieve a reading as low as 010. Is this normal? > > C55 was a bit stiff and seems rather critical in its adjustment. I > momentarily got a reading of 003 but lost it as I tried to go lower and now > 010 seems as low as I can get. ++++++++++++++++ Date: Sun, 08 Sep 2002 11:45:33 -0500 To: "Peter Halpin" , elecraft at mailman.qth.net From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] KAT2 set-up problems Pete: >I'm having some trouble setting up my KAT2 bridge null (CALn). > >Whatever I do I can't get the reflected voltage under about 7mV, and if I do >get it that low it tends to vary a little - generally between 7 and 11. I am >using a dummy-load that is good up to above 1.5GHz, so I don't think that >that could be the cause of the problems. I have replaced the capacitor with >an miniature air-dielectric model because the one supplied seemed to be a >bit dodgy, and I have of course checked the SWR bridge several times, even >going so far as to re-wind the transformer - but I can't get a reading lower >than 7-11mV. > >Can anybody give me a nudge in the right direction, please? Or am I worrying >about nothing? What you are obtaining should be COMPLETELY adequate! If you are using a DMM for the voltage measurement, try replacing it with an analog meter... MUCH easier to use and no 'bobbling' bacn 'n forth between readings. 73, Tom Hammond N0SS ++++++++++++++++ Date: Fri, 13 Sep 2002 08:45:15 -0500 To: "Alan J. Price" , elecraft at mailman.qth.net From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] KAT2 No Null Hi Alan: W1HYV wrote: >What are some typical reasons why I can't get a null of any sort while >adjusting C55? Have checked parts and T1, all are proper and appear to be >OK. Generally, the wiring of T1 is the culprit... wrong lead placement! Seems we've had a spate of this recently. Additionally, crank C55 thru a few full-rotational cycles... maybe 8-10, and see if this helps. Some of the trimmer caps still want to exhibit some lack of patent connection initially. Hang a voltmeter at both the FWD and REF outputs (at the TOP end of each pot) and see if you can see any DC voltage there when you transmit. This will tell you if you are developing ANY measurable output voltage thru the directional coupler. If you get one, but not the other, investigate to see why. 73, Tom Hammond N0SS +++++++++++++++ From: "Alan J. Price" To: "Elecraft" Date: Fri, 13 Sep 2002 10:18:05 -0400 Subject: [Elecraft] Null answer I found the problem. It was the nut in front of the K2 causing the problem. I had the dummy load in the wrong BNC output. Talk about dummies. Alan ++++++++++++++++ From: "garigue" To: "Stephan Walder, HB9DDO - K2" , "'Elecraft'" Subject: Re: [Elecraft] KAT2 problem: bridge null adjustment Date: Tue, 21 Jan 2003 18:09:32 -0500 Stephan Hello .... Tom KI3R nr Pittsburgh .. I had the same problem and I was pulling my hair out. I sent the unit back to repair and a solder bridge was found beneath one of the torroids. The bridge was on one of the relay pins ..and I double checked them when I did the soldering but I missed. I must have redid that darn T1 4 or 5 times!!!! The unit works excellently now and is a real pleasure to use in the field and on vacation. God Bless KI3R Tom ----- Original Message ----- From: "Stephan Walder, HB9DDO - K2" To: "'Elecraft'" Sent: Tuesday, January 21, 2003 4:10 PM Subject: [Elecraft] KAT2 problem: bridge null adjustment > Hello K2-owners > > I'm on the way to assemble/install the KAT2 option. Everything looks good > including the preliminary tests. When I came to the point where I'm supposed > to adjust C55 for the bridge null I ran into problems. Even with power > reduced to the minimum at 0.1W I get a high current warning when I tune. I > checked several times to make sure that the dummy-load/rf-power-meter is > conncted to the right Ant jack (1) and the correct antenna is selected. My > K2 reacts as if there were no antenna at all. I even checked the cable > between TX and dummy-load, went back totest without KAT2 to make sure > there's no problem there. > > According to the troubleshooting section I checked on T1, even re-soldered > it to make sure there's no problem there... > > Fellow hams, I'm stuck ! Any help/idea/suggestion is welcome. Anybody seen > this or a similar behaviour before ? > > vy 73, Stephan, HB9DDO, K2 S/N 3128 +++++++++++++++ From: "Stephan Walder, HB9DDO - K2" To: "'Elecraft'" Subject: Re: [Elecraft] KAT2 problem: bridge null adjustment Date: Wed, 22 Jan 2003 21:49:21 +0100 Hello all problem solved, thanks for all the supporting remarks that came back. It's great to have so many helpful friends out there around the world... If you're interested to know what was wrong, please read on... If you're interested to learn about some of the lessons I learned, please read on... Please don't read on, I feel like a complete idiot and just hope none of the guys I work with read this, my reputation will be gone... What went wrong: actually two things were wrong as I learned tonight first reading all your comments and then going calmly over the troubleshooting section again: actually the second last sentence in the troubleshooting section that applies to my problem (can't get a reading of 010 or lower in CALn) reads as follows: "Make sure you dont have the center conductor and the shield exchanged at J7." Guess what ? They were exchanged. Ok, that was the first time I felt a little foolish after annoying the email-list with something that was well described in the manual; at the same time I thought: well you can easily fix that little stupid... So I did, assembled everything again, run thru the test agian and guess what ? Same behaviour. Ok, what's next ? Read over your email comments and thru the manual again or just put the project aside for tonight and get a good book ? This thought lasted for about 7 seconds then I took the assembly apart again (hey, the drill did me good, I'm real fast by now with this part ;-) and started to check all the solder joints on the relays, T's etc. And than it sprang right in my eye: to much solder causing a connection between pins 7&8 on P5 and and L5 - obviusly this doesn't help a lot trying to get RF out of the thing. The rest is well known history to all of you who completed the KAT2: the needle on the RF-meter came alive immediatly, some playing around with C55 (finally getting it down to 009) and so on... The ATU seems to work nicely, managed to get the SWR down to 1.3 or better on all bands from 80 to 10 on my short G5RV - remains to be seen how good the antenna actually works in my location. Lessons learned: ok, now for the other part of the story. For how many times did I read the discussion about taking your time when building the kit, actually enjoying this part etc... And I ignored it... 1) working too long on the K2, deep into the night, after a hard days work rellay doesn't help 2) trying to keep the kids busy with the Internet on a late sunday afternoon after we all spent a couple of hours out in the snow and sun and then trying to assemble something easy like J7 is definitely NOT a good idea Two lessons learned ain't enough ? Well first of all I'll try to remember the when starting with the next option kit ;-) Now I'll turn over the bands once more and then I'll read a book. The fun will be next weekend: there's to hand out a few points in the CQ DX 160m and hopefully collect a few new ones on the top band (that'll be QRO, the 160RX option is not built yet), then there's a friend of mine who'll see and touch the K2 for the first time (but who heard me talking about nothing elseever since I ordered it in mid-december and last but not least I hope I can catch N4BQW/KH9 for my DXCC #311 :-) Ok dear fellow hams, thanks again for your support and I look forward to meet you on the bands ! 73, Stephan, HB9DDO, K2 S/N 3128 ++++++++++++++++