I think he would be better off throwing away the window line and eliminating the tuner.
Cut the length of the dipole for resonance on 40M and then add a 20M dipole in parallel at the feed point. There will be some interaction, which can be lessened by orienting the dipoles at right angles to each other or at least getting some angular separation. Conventional wisdom (not always correct) says to use a 1:1 current balun at the antenna. With only 10W you don't want to be throwing it away in lossy tuners and mismatched transmission lines. Wes N7WS ps. The only tuner I use in my shack is the pi-net in my L4-B. --- On Fri, 1/15/10, Don Wilhelm <[email protected]> wrote: > From: Don Wilhelm <[email protected]> > Subject: Re: [Elecraft] [OT] High SWR on 20 and 40 > To: "djmd" <[email protected]> > Cc: [email protected] > Date: Friday, January 15, 2010, 1:45 PM > Dave, > > Is that a 1:1 balun or a 4:1 balun. Usually a 1:1 > works better, but > whichever balun you are using, try the other one and see > what happens. > Do you have an antenna analyzer? or can you borrow > one? If so, what is > the impedance at the end of the coax? Both the > resistive and reactive > components please - just the SWR does not provide much > information on > how to advise you to proceed. > > You may be better off eliminating the coax entirely and > running the > window line all the way into the shack. > 73, > Don W3FPR > > djmd wrote: > > Hello, > > > > I have been trying to troubleshoot my antenna system, > and have been trying > > to avoid the dreaded "high swr" post, but I've run out > of ideas, so I'm > > turning here. > > > > First let me explain my system. 67' dipole fed by 16' > of window line. That's > > connected to an Elecraft balun. From the balun, > there's a short piece of > > coax going to a barrel and into the basement (through > a piece of cement > > backerboard. From inside the basement, there is > another piece of coax, about > > 12', connected to the barrel, and going up into the > bedroom directly to a K2 > > with an autotuner. > > > > Before the K2, I was using a Yaesu FT840 with an MFJ > tuner. After tweaking > > the window line length and the actual length of the > dipole, I never really > > had a problem with SWR (well, according to what the > MFJ was saying, which > > may or may not be totally accurate.) Usually 1.5:1 or > under on all bands. > > > > With the K2/KAT2 in place, the SWR reported by the > tuner is all over the > > place. The only one that gets less than 1.5:1 is 30m. > Most bands are pretty > > random, anywhere from 3:1 to 7:1. However, on 20 and > 40, it generally does > > not get below 9.9:1. > > > > I've tried 4 different lengths of coax between the > barrel (inside) and the > > rig... 3', 6', 12' 20'. I've tried a couple different > lengths between the > > balun and the barrel on the outside. > > > > When I attach the balun directly to the K2 I get > <1.3:1 on all bands (most > > are 1:1.) With a short piece of coax between the rig > and the balun, I get > > the same results. I've also attached my dummy load to > the barrel on the > > outside of the house, and tested it from the shack, > and I saw 1:1 no > > problem. > > > > I totally understand the concept that if "A" works and > "B" works, "A+B" > > doesn't necessarily work. I understand it's a whole > system. But I've tried > > so many different combinations of coax on each side, > and don't understand > > why my SWR is basically infinity:1 on 20 and 40, when > they seemed to match > > reasonably with the old system. I have not tried > different lengths of window > > line between the dipole due to the fact that I had it > perfectly trimmed for > > my old system. But I have plenty of it and would be > open to trying anything. > > > > Just trying to get the most I can out of my modest > 10W. :) Any suggestions > > would be appreciated! > > > > 73, > > > > Dave > > K8DJW ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
