Dave - If an antenna suddenly changes its behavior, the cause is usually a broken connection somewhere, or a problem with the feedline, either shorted or open. So check these all first. It is easy for there to be a break in the ladder line, particularly if it uses a solid conductor that is hard to detect. Use an ohm metro from one end to the other. You should also look at the antenna with and without the balun (1:1) position) in place, the tuning shouldn't change a whole lot. If it does, look at the balun construction for a poor connection or bad solder joint. An antenna analyzer is a big help here, if you don't have one, I am sure that you can borrow one if you ask at a club meeting or speak up on the local repeater.
Having said that, if everything is in good shape, the first thing I suggest that you do is to model the antennas and transmission line and see what impedances you can expect to see where. This will help you understand what to do to match the antenna or where there are problems. Otherwise you are pretty much flying blind. Get a good antenna modeling program, something like EZNEC, even the trial demo version will work for your case: < http://www.eznec.com/ > MMANA will work too and is free: < http://www.smeter.net/antennas/mmana.php > Model your antenna. You should see a reasonably low impedance on 80M, a high impedance on 40M, a moderate impedance on 30M, a high impedance on 20M, and well you should really do the modeling to get precise values. You will probably see a lot of loss on 80M as the antenna appears to be less than 0.1 wavelengths high. Anyway, record these values on the different bands. The 16 ft of ladder line acts as a transformer to transform the impedance. You can calculate what the transformation will be with transmission line program; TLW is included with the Antenna Book and is good; W9CF has a nice java based app on the web: < http://fermi.la.asu.edu/w9cf/tran/ > which you can also download and run locally. It is nice as it runs on any machine that runs Java. You can also see how to do the transformations by hand in the Antenna Book. Now, enter the antenna impedance values into the transmission line program and see where they get transformed. You will need to do this twice, once for the antenna - ladder line - coax run and once for the balun - coax - tuner run. Use the balun at 1:1 for the time being. You should try to borrow an antenna analyzer to verify your calculations, although with the high impedances the analyzer may not give too useful results. None of these will be exact, but they should be in the ball park and give you an idea of what you should be doing to get a match. This procedure will tell you what impedance you are expecting the tuners to tune. My guess is that it is within the range of your tuners and that you have a problem elsewhere, but do the math. If the impedance is outside the range you are expecting to tune, then you can change antenna or transmission line lengths until you get a match that is acceptable. That is far better than cutting and adding line and antenna lengths without an idea of what to expect. The 16 ft of ladder line will have different effects on different bands. On 80M the electrical length of the transmission line will be small and you won't see much transformation. It is pretty much equivalent to lengthening the antenna. You should still see a low to moderate impedance here that the tuner is capable of matching. On 40M you will see more effect, but I suspect that the impedance will still be very high, perhaps too high for the tuner to match. On 20M the line length is a quarter wave, which should transform the high antenna impedance to a low to moderate impedance which the tuner can match easily. The K-2 is pretty portable so you could try hooking it up to the antenna at the various junctions and see what happens. You should be able to get a match on 20M at the end of the ladder line. Try it with and without the balun in the 1:1 position. If that doesn't work, I suspect that you have problem in the K2 tuner or SWR circuit. You should be able to get an acceptable match with or without the balun, it won't be the same, but it should be close. You may or may not get a match here on 40M with the 1:1 balun, but you should get one with the 4:1 balun. While the first thing I Would do is look for shorts or opens or bad connections in the system, you should probably read the Antenna Book chapter on transmission lines to get a feel for what is happening to the impedance at the various transmission line junctions. Having encouraged you to measure and model, my gut feel is that you should be able to match this system with the K2 tuner and the 4:1 balun on all bands above 80M. I suspect that you have a problem in the antenna feedline and connections somewhere. Let us know how this all works out and if you have further questions, feel free to ask. - Duffey -- KK6MC James Duffey Cedar Crest NM ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
