+++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: Subject: RE: [Elecraft] Antenna Question Date: Sun, 24 Mar 2002 10:35:36 -0800 >...I'm thinking of a 67ft wire from the roof > to a tree, > end feed with about 30ft ladder line comming into the upper floor "shack". > The ARL handbook indicates a transmatch is needed. ...Any thoughts or > recommendations will be appreciated. >> john > va3jsl at rac.ca That's sort of a Zepp antenna. They are VERY frequency-sensitive if you want to avoid a lot of radiation from the feeders. The original Zepp used a 1/2 wave radiator and a 1/4 wave long feeder. You provide balanced feed to the open wire line at the rig. At the other end ONE side of the feeder goes to the radiator and the other side is insulated and connected to nothing at all. The 1/2 wave radiator shows a high impedance at the end where it is fed, so very little current is drawn from the feeder. It is a classic "voltage" feed with very high r-f voltages at that point. Since the current in the side of the feeder going to the antenna is very low, and the current on the side of the feeder that connects to nothing is also very low (only whatever leakage there is through the insulator), the currents in the feeders will be fairly well balanced, preventing radiation from the feeder. The 1/4 wave long feeder transforms that very high impedance into a low impedance at the ATU in the shack, which keeps the r-f voltages there low. The moment you move from the frequency where the radiator is exactly 1/2 wave long it will start to 'draw current' from the feeder. Since only one side of the feeder is connected to anything, that will unbalance the currents in the feedline and it will begin to radiate. Still, it can be an effective antenna, although at any but the design frequency it is more like a simple 'end fed' wire with the antenna coming right down into the shack. Also, on some frequencies you will develop very high r-f voltages at the ATU end of the feeder. One time I literally burned up a 300 watt balun (and melted a nylon binding post) running only 10 watts! I was using an end fed Zepp on various bands and hit a combination that put the voltage loop (high impedance point) at the ATU. Even at 10 watts there was plenty of r-f voltage to arc between windings on the balun and melt the insulation on the binding post. You might do as well or better by simply end-feeding the wire since you are already on an upper floor. The KAT2 should handle that just fine. If it has trouble on one band, just change the antenna length a couple of feet and you should be able to find a length that it can handle on all bands. You will want to use a tuned counterpoise - a 1/4 wave long wire for each band - one end connected to the K2 case and the other end insulated. They can be run anywhere as long as they are insulated. On bands where you have a high impedance at the rig they will keep the K2 at r-f ground and avoid problems with 'r-f in the shack'. On bands where the antenna presents a low impedance at the rig, the counterpoise is essential to provide an efficient r-f ground. Without it, most of your power will be lost in the poor 'ground' connection instead of being radiated. Be careful though, the far end of the counterpoise can cause r-f burns if someone touches it. An alternative to separate counterpoise wires is to use an "Artificial Ground" like MFJ sells. It's a simple L-match and r-f ammeter that you use to tune a single counterpoise wire to 1/4 wavelength at the operating frequency. That provides a good 'r-f ground' at the rig end. I have used one with very good results. I have used one successfully with a counterpoise wire that was as little as 1/16 of a wavelength long on the operating frequency (16 feet on 80 meters) although I believe that Moxon suggests about 1/8 wave as a suitable 'minimum' counterpoise length. If you are where must have a fairly long run before your antenna is out of the shack and 'in the clear', you might want to consider a balanced antenna instead - a doublet fed with the open wire line in the center. With balance feed you will avoid radiation on the feeders as long as the two halves of the antenna are the same length and fed from a well-balanced source. It will work well on any frequency down to where the 'flat top' is 1/8 wavelength long. One of my favorite books for all manner of interesting and effective wire antennas and tuner designs is a little book by John D. Heys, G3BDQ, called "Practical Wire Antennas - Effective HF Designs for the Radio Amateur". Published by the Radio Society of Great Britain (ISBN 0 900612 87 8) it is available from several sources, including the ARRL here in the USA. Ron AC7AC K2 # 1289 ++++++++++++++++++ From: "Ron D' Eau Claire" To: Subject: RE: [Elecraft] Antenna Question Date: Sun, 24 Mar 2002 11:00:56 -0800 Whups! In my previous post I meant to say that a doublet will work well down to the frequency where the flat top is 1/4 wavelength overall, not 1/8 wavelength. Ron AC7AC K2 # 1289 +++++++++++++++++++ Date: Sun, 24 Mar 2002 14:02:25 -0500 To: "John Lucas" From: Charles Greene Subject: Re: [Elecraft] Antenna Question Cc: At 10:46 AM 3/24/2002 -0500, John Lucas wrote: >Now the K2 RF board is comming nicely I need to get the antenna up. > >Because of limit space I'm thinking of a 67ft wire from the roof to a tree, >end feed with about 30ft ladder line comming into the upper floor "shack". >The ARL handbook indicates a transmatch is needed. Will the K2 ATU work >this configuration or do I need a transmatch or both? If I need the >transmatch can anyone provide a link to a good design? --Snip-- John, I use a W3edp antenna which is 85' of wire with a 17' counterpoise. On 40-15, the 17' counterpoise acts as one side of a open wire ladder line and the antenna is a voltage fed antenna, but on 10 and 80, the antenna is current fed. So I added a 67' and a 8' counterpoise for 80 and 10 in parallel with the 17' one. 25' of the wire goes from my basement up the side of the second floor, then 60' to a tree. Where the three counterpoise and wire meet, I use a 4:1 balun. The counterpoise are just tacked on the side of the house at about the 3' level, but they can go anywhere. For the balun I have used a Radio Works 2KX current balun or a home made current balun consisting of two cores with 13 turns #24 wire each biflar wound on FT114-43 cores. The balun is connected to length of coax which then goes to the K2AT. Works fine 160-10, and the balun does not experience excessive loss. It is operating about 97% efficiency and will take 100 watts easily. The Lengths of wire are such that the SWR at the intersection of the antenna and counterpoise is moderately high on all bands but not so high that it will damage the balun. In comparison to other antennas, it is about an S unit less than my G5RV at 35' and my Hustler 6BTV. It would work better on the lower bands if it were higher. A 67' length of wire if fed with open wire line will be a voltage fed antenna on 40, 20, and 14, and with an 18' length of open wire line, will function as W3EDP antenna on those bands and will probably ok work on 30, 17, and 12 too if you run a coax from the balun to the K2AT as I did. You might have to try some different lengths of coax, and the coax will have moderately high losses. You will have to do something else on 80 and 10. A transmatch has a single ended output so you will need a balun somewhere to convert balanced to unbalanced. There are other types of tuners for balanced lines. An old Johnson Matchbox, if you can pick one up at a flea market or on the internet, will tune a wide range of open wire impedances. I have one, but it is not for sale. 73, Chas, W1CG +++++++++++++++ Date: Mon, 25 Mar 2002 07:53:23 -0500 (EST) From: baltimoremd at baltimoremd.com To: John Lucas Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] Antenna Question On Sun, 24 Mar 2002, John Lucas wrote: > Because of limit space I'm thinking of a 67ft wire from the roof to a tree, What works for me and my K2 is an 87 foot end fed wire with a counterpoise for each band I want to work.... 73 Thom ++++++++++++++++++ Date: Mon, 25 Mar 2002 13:14:08 -0500 From: Mychael Morohovich To: john at jlstechnology.com Cc: elecraft at mailman.qth.net Subject: [Elecraft] Re: antenna question >>Because of limit space I'm thinking of a 67ft wire from the roof to a tree<< Sounds as though Tom and I have a similar arrangement. I use what is called a W3EDP antenna which essentially consists of an 85' wire and 17' counterpoise. With the KAT2 I find that the antenna loads easily on all bands, with the exception of 15 meters (I cure that with the addition of a series inductor between K2 and antenna). I do use an artificial ground to tune my counterpoise, although this purportedly is not necessary. The antenna does not have to run in a straight line; mine has a 12' vertical section running from the entry point at the shack up to the roof line. From there it traverses my back yard to a halyard attached to the top of a large tree. The counterpoise can be tossed onto the floor or routed around the shack however convenient. There will be voltage present on it, especially at its end, so care should be taken to insulate it well or keep it clear of kids and pets or even curious wives. I run mine outside and then down into the basement where I can attach it to the house ground with a croc clip at its end. (By doing this and reversing the counterpoise and W3EDP I am able to easily tune up 160 meters. While I admit to only a few QSOs on top band, my first took place with an op 900-1,000 miles away.) This antenna, as well as a "gallimaufry" of others is described in great detail in the excellent book "Practical Wire Antennas" by John D. Heys- G3BDQ. Hope that this helps, Mychael Morohovich /AA3WF K2#1025 ++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: "Elecraft List" , "Jim and Kate" Subject: RE: [Elecraft] Antenna Question Date: Mon, 25 Mar 2002 18:23:40 -0800 > Kurt reviewed all the cautions, then built a 40M Zepp end fed. He > reported > "NO RF in the shack!" from the feeder. > Yes, you do have to use a transmatch on other bands than the resonant > one. > I am > thinking of trying one to see if it holds true for my location. > Location > and nearby conductors can cause problems for any antenna. Yes, high > impedance end feed might have some issues, but it is a low current point > as > well. Stuart's absolutely right, Jim. At the resonant frequency, it will have NO r-f in the shack because the feeders offer a good balanced termination for the transmitter. That was the whole idea behind it for use on the Zeppelins. But remember that at any frequency other than the one where the antenna section is exactly 1/2 wave, the antenna is a simple random wire coming down to the ATU. The "other side" of the feedline is now non-functional. If you are using a balun feed, disconnect it. It can do nothing for you but cause problems (like I had with arcing) and losses. Actually you need some matching device on the resonant frequency too. It is a low impedance feed when the feeders are 1/4 wavelength long, but not necessarily anything near 50 ohms. That depends upon the exact electrical length of those feeders. Of course, back when the Zeppelins were flying everyone used an ATU and open wire feeders . The fact that the feedline is just part of the radiating antenna on other frequencies is certainly no problem in most installations. Such a 'random wire' antenna can work GREAT, especially if a good part of it is up in the clear. You will need a good counterpoise on any but the resonant frequency though. Either to ensure good efficiency (when the feedpoint impedance is low) or to keep r-f from floating around the shack on those frequencies where the impedance is high. That's what gave "end-fed" wires a bad reputation. Many Hams did not understand the need for a good "r-f" ground and found themselves getting r-f bites off of their rigs, etc. They blamed the antenna instead of the lack of a good r-f ground. One way of looking at the Zepp is that it has a built-in "counterpoise" for the frequency for which it is designed. That 'unconnected' side of the feeder is exactly 1/4 wavelength long at that frequency. The far end will be at a high impedance since it is insulated and not attached to anything, so that forces the other end - at the rig- to be at a LOW impedance. Hence it is at a good 'r-f' ground. There really is NOTHING unusual or 'magic' about a Zepp. It works exactly along normal antenna principles. The idea was to provide a good antenna for an airship aloft that had a minimum of r-f radiation within the airship itself and which could still end-feed a 'trailing wire' antenna floating out below and behind the airship. But, like many circuits in the Ham world, it developed a 'mystique' all its own . Ron AC7AC K2 # 1289 +++++++++++++++++ Date: Tue, 26 Mar 2002 06:12:00 -0500 To: From: Charles Greene Subject: RE: [Elecraft] Antenna Question Cc: "Elecraft List" At 06:23 PM 3/25/2002 -0800, Ron D' Eau Claire wrote: Ron et el, An end fed 1/2 Zepp antenna on 40 will be full wave end fed antenna on 20, a 3/2 end fed antenna on 15 and a 2 wave length end fed antenna on 10. All can be fed in a similar manner. You don't need a specific length of feed line for an end fed zepp but if you use a multiple of 1/2 wave length, the high voltage current node will be in the shack. If you are using a transmatch with a balun, the high voltage will be bad for the balun and it could destroy it. My experience on baluns is that they will work up to an impedance of 500-700 ohms or so, but the impedance of the current node is several thousand ohms. > > Kurt reviewed all the cautions, then built a 40M Zepp end fed. He > > reported > > "NO RF in the shack!" from the feeder. > > Yes, you do have to use a transmatch on other bands than the resonant > > one. ++++++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: "Elecraft List" Subject: RE: [Elecraft] Antenna Question Date: Tue, 26 Mar 2002 08:03:08 -0800 Chas, W1CG > An end fed 1/2 Zepp antenna on 40 will be full wave end fed > antenna on 20, > a 3/2 end fed antenna on 15 and a 2 wave length end fed antenna > on 10. All > can be fed in a similar manner. Right, Charles! Critics will point out that the feeder imbalance well be progressively worse on the higher harmonics because the maximum impedance of a "long wire" is lower as the harmonic is increased and a wire with insulators at the end does not resonate at exact multiples of the fundamental frequency. Both of these effects are probably not significant to most hams, but it's good to realize that a "Zepp", unlike a center fed balanced antenna, will tend to show greater feeder radiation quickly as compromises are made in the dimensions. My experience with baluns feeding an open wire line when it presents a high impedance at the ATU fit with yours. I "smoked" my large balun and an insulator in the ATU running low power by trying to use a 40 meter Zepp on 20 where the feeder was 1/2 wavelength long. Ron AC7AC K2 #1289 ++++++++++++++++++++ From: "Stuart Rohre" To: , "Elecraft List" , "Jim and Kate" Subject: Re: [Elecraft] Antenna Question Date: Tue, 26 Mar 2002 13:59:41 -0600 Ron has summarized quite well, what I think Les Moxon was trying to get across in his write up on the Zepp. Not yet mentioned for the newbies, is the end fed Zepp is more commonly seen today as the VHF J pole. The same antenna with a 90 degree angle removed from its feeder/matching stub. Of course, the J poles generally have been one band antennas, but the cactus J pole often adds 440 to 2M,and I think someone even tacked on a 222 antenna. In a recent ARES group meeting in Williamson County, TX, we built some J poles of 1/2 inch copper pipe. For convenience, we mounted antenna jack on the short side pipe, and drilled a thru hole to carry a right angle insulated wire from the center post of the connector inside the short stub, and back out to tap onto the longer pipe element. Much to my delight, I discovered we had both 2M fundamental good match, and a good one at 440 without adding any "cactus" elements! Apparently, placement of the type UHF connector facilitated a multi band match. I think the spacing from short stub to main pipe was 3 inches, for those wanting to try this. But, before you do, I will check on the right spacing. For K2 use, a J pole for 10M is feasible, but 3/4 pipe would make a sturdier radiator and stub. 72, Stuart K5KVH +++++++++++++++++ Reply-To: "Don Wilhelm" From: "Don Wilhelm" To: , "Charles Greene" Cc: "Elecraft List" Subject: Re: [Elecraft] Antenna Question Date: Tue, 26 Mar 2002 20:51:23 -0500 Charles and all, What you say is true when only the radiating part of the antenna is considered - but the true Zepp antenna is a system 'thing' and consists of both the radiating portion and the 1/4 wave feedline. Ham usage has construed the label "Zepp" to be most any end fed antenna a half wave long, and that is not always a true Zepp antenna. I know it is only semantics - but I feel that in the instance that initiated this thread, it is important - even if I don't usually agree with Kurt. 73, Don Wilhelm - Wake Forest, NC W3FPR home page: http://www.qsl.net/w3fpr/ QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net *** Life is what happens when you're making other plans -- Mike Cross *** ----- Original Message ----- > > An end fed 1/2 Zepp antenna on 40 will be full wave end fed antenna on 20, > a 3/2 end fed antenna on 15 and a 2 wave length end fed antenna on 10. All > can be fed in a similar manner. You don't need a specific length of feed > line for an end fed zepp but if you use a multiple of 1/2 wave length, the > high voltage current node will be in the shack. If you are using a > transmatch with a balun, the high voltage will be bad for the balun and it > could destroy it. My experience on baluns is that they will work up to an > impedance of 500-700 ohms or so, but the impedance of the current node is > several thousand ohms. ++++++++++++++++++++ Reply-To: "Ron D'Eau Claire" From: "Ron D'Eau Claire" To: Subject: Re: [Elecraft] antenna question Date: Thu, 23 May 2002 22:03:33 -0700 >... extended double zepp > with a transmatch. My question is, given that I use a > transmatch anyway, am I better off putting up 137 feet or 142? I've often > felt, "get up as much wire as you can." But being so close to a half wave > makes me wonder. Any thoughts? > dave belsley, w1euy You are using my favorite wire antenna, Dave! The issue over the length is strictly what it does to your feedpoint impedance and that depends upon the electrical length of your feeders of course. I'd go for 142 feet and shorten the antenna as needed only if you have trouble loading on some bands. The difference in the "gain" of the antenna in its most favored directions is going to be very slight even if you shorten it by another 10 or 20 feet. You will still get lobes showing gains over 10 dbi up on the higher bands. If your transmatch uses a balun at the output to provide balanced feed and you are concerned about whether it is still providing a balanced feed on bands where the impedance appears to be very high or very low, I suggest checking the currents in the lines for balance. Two r-f ammeters with sufficient accuracy to see a 10% or 20% unbalance can be had very inexpensively at most stores. They are called "flashlight bulbs", Hi! I have a couple of little sockets that mount some 12 volt screw in bulbs that I use for high current feeds. When the impedance is very high, the current will be very low, and I have a couple of 2.5 volt 25 ma "grain of wheat" bulbs with clips on the leads that show relative currents there. They are very easy to "blow" though - especially with the K2 if you forget to turn down the power THEN transmit so the power control circuits react to the change BEFORE inserting them in the line. I can get useful indications at only 1 or 2 watts on most bands. I ran a few tests using DC to see how much of a difference in currents was readily apparent in the bulb brilliance, and I found that as long as they are only lit dimly it was easy to see a 5% or less difference. I've had great success using them down to where they are only 1/4 wavelength long, provided they are high enough off of the ground. That would suggest that it would still do an efficient job for you on 160 meters if you like to operate there. In my tiny space, I am presently using a shorty 42 -foot center fed doublet with high quality ladder line. It's just about an "extended double Zepp" length on 10 meters, but it works FB on 40 through 10 meters. Ron AC7AC K2 # 1289 +++++++++++++++++ Date: Fri, 24 May 2002 00:29:45 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: "David A. Belsley" Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] antenna question You will probably never notice the difference between 175 ft and 145 ft except perhaps a bit on the lower bands. The tuner will adjust differently, but I really doubt that will see much difference in operation. I would keep the 145 feet rather than cut it to 137 feet (why a resonant antenna when you are tuning the system anyway?) but if you can droop the ends down 15 ft, you will still have your 175 feet with neglgible effect on results. It may tune a little differently, however. Remember that the ends will be a a relatively high r-f voltage, even with 5 watts, so make sure that no one can come in contact with them. I am a firm believer in non-resonant antenna lengths when using ladderline and a tuner. That way you have smaller variations in feedline input impedance that you do with resonant flat-tops. Besides, the antenna will never show a driving-point impedance of 450 ohms resistive on any band, so the antenna length is highly non-critical from that aspect - just so it reaches from one tree to the other! <:} 73/72/oo, George W5YR - the Yellow Rose of Texas Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR, in the 56th year and it just keeps getting better! QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735 Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437 "David A. Belsley" wrote: > > Well, the ol' K2 has been very happy with my 40 meter extended double zepp > with a transmatch. It has a flat top of about 175 feet, and it's done > beautifully 160-10. But one of the trees it is anchored to is > disappearing. My alternative gives me a stretch of roughly 145 feet max, > probably 142 feet to play it safe. Of course, half wave for the bottom of > 80 meters is roughly 137 feet. My question is, given that I use a > transmatch anyway, am I better off putting up 137 feet or 142? I've often > felt, "get up as much wire as you can." But being so close to a half wave > makes me wonder. Any thoughts? > > thanks, > > dave belsley, w1euy +++++++++++++++++++ From: "Stuart Rohre" To: "George, W5YR" , "David A. Belsley" Cc: Subject: Re: [Elecraft] antenna question Date: Fri, 24 May 2002 14:55:26 -0500 Folks, George hit it on the head. There are more reasons to use non resonant antennas fed with parallel line than to worry about measuring and cutting them to resonant length. You are using the transmatch to make that unneeded. Many handbooks and introductory texts start out talking about resonant dipoles just as a way to teach the basic theory. But that does not mean they are more efficient than a transmatch and parallel line fed doublet of some length. That early intro to resonance gets misinterpreted by new hams as giving resonant dipoles some magical property over non resonant lengths. The resonant dipole is an advantage only on a single frequency, and you need a transmatch everywhere else, so why bother with measuring to resonance? Who works only a single spot in the band? Or a single band? A resonant antenna is higher Q, and might spike the impedance such that the transmatch has to be adjusted if you try to cover another frequency in the same band that is nearby. With a broadly tuned doublet that is not resonant on any band you are using, except perhaps the lowest, you can move around not only on frequencies in a band but from band to band with some easily determined settings of the transmatch, that can be returned to when you QSY. A simple chart sets you up to return to any spot on any band. A few settings work over any one band for our Field Day big loops and Double Zepps. The losses of parallel line are much lower feeding broad coverage doublets than if you tried to use coax for multibands. The measurement of doublets for many bands is simply as George says, have wire to stretch from one support to the other. Fold it in half to find the middle, and cut it there and insert feedpoint insulator, and your feeder. That way you do not need to carry a long tape measure to field days, or emergency set up locations. If your doublet is long enough at a given band, you can realize gain over a dipole. It is the truly multipurpose antenna. 72, Stuart K5KVH +++++++++++++++++++ Reply-To: "Don Wilhelm" From: "Don Wilhelm" To: "Stuart Rohre" , "George, W5YR" , "David A. Belsley" Cc: Subject: Re: [Elecraft] antenna question Date: Fri, 24 May 2002 18:41:16 -0400 Folks, I agree 100%. Now there is just one word of warning to those trying a non resonant antenna for the first time --- some flattop/feedline combinations may present a feedpoint impedance that will make then hard to tune with the tuners commonly available today. If that occurs, there are 2 possible cures - add or subtract some feedline (don't know how much - you will have to experiment), or add some wire to the antenna ends - just let it hang down if necessary. Three to 5 feet added to each end makes a difference at 40 meters - less at 80, and even more difference at the higher frequencies. Remember that if a 'leg length' is close to a half wave will be hard to feed with all but a parallel tank circuit type balanced tuner (we can't hardly buy these now-a-days). The leg length that I am referring to is the length of half the flattop plus the electrical length of the feedline (this is length/0.95 for window line). You did measure your feedline didn't you??? It helps in figuring what the matter may be. 73, Don Wilhelm - Wake Forest, NC W3FPR home page: http://www.qsl.net/w3fpr/ QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net ++++++++++++++++++ From: N2EY at aol.com Date: Fri, 24 May 2002 20:07:41 EDT Subject: Re: [Elecraft] antenna question To: w3fpr at peoplepc.com, rohre at arlut.utexas.edu, w5yr at att.net, belsley at bc.edu Cc: elecraft at mailman.qth.net In a message dated 5/24/02 6:47:11 PM Eastern Daylight Time, w3fpr at peoplepc.com writes: (some good stuff about dipoles snipped to save space) > Remember that if a 'leg length' is close to a half wave will be hard to feed > with all but a parallel tank circuit type balanced tuner (we can't hardly > buy these now-a-days). Yes, but we can build them! > The leg length that I am referring to is the length > of half the flattop plus the electrical length of the feedline (this is > length/0.95 for window line). You did measure your feedline didn't you??? > It helps in figuring what the matter may be. The following website has some simple but useful freeware: http://www.g4fgq.com Program DIPOLE3 lets you describe any dipole/feedline combination, and will tell you the expected efficiency, SWR and feedpoint impedance. (It won't tell you the pattern, though). Program ENDFEED does the same for end-fed wires. Lots of other neat stuff. These are simple DOS-based programs. They are small, run on almost any computer and the instructions are built-in. You may have to convert to metric units but that's no big deal. Many hams use unbalanced tuners and wound-core baluns to feed balanced lines. This method works OK if the feedpoint Z is close to the impedance that the balun is designed to see. It can work very poorly otherwise, causing all sorts of odd effects. The obvious answer is a balanced tuner. This problem, and an easy solution, was described in QST back in February, 1990, by AG6K. A recent QST article also dealt with it. Online, see: http://www.vcnet.com/measures/bbat.html Although he uses ganged roller coils, there's no reason switched coils couldn't be used instead. Note that this design works for balanced or unbalanced loads. Standard disclaimer: I have no connection to either of these hams except agreement with and admiration of what they have written. The KAT1 and KAT2 are unbalanced tuners. Feeding their unbalanced output to a balun and balanced line is an iffy setup. Elecraft could lead the way (hint hint) by producing a true automatic balanced tuner, using switched coils instead of the ganged roller inductors used in the above article. Only downside would be that twice as many toroids would be needed.... 73 de Jim, N2EY +++++++++++++++++++