You don't need to add 8 foot wires for 10 meters. The 80 meter dipole will load up there with a little help from the tuner.
73, Tony K4QE On Sat, Dec 8, 2012 at 7:27 PM, Ron D'Eau Claire <[email protected]> wrote: > > If you want to use your 40 meter dipole on 20 meters, one way is to add two > 16 foot wires at the center feed point, putting a 20 meter dipole in > parallel with the 40 meter dipole. On 40 the extra 16 foot wires will > simply > make the radiator look a bit "fatter" to the RF. On 20, the 40 meter dipole > exhibits a very high impedance at the feed point (which is what is causing > your problem now) while the 20 meter dipole will present a decent match. > > Your 40 meter dipole already makes a decent 15 meter antenna because it's 3 > half waves long, with a relatively decent match at the feed point. > > In the extreme you could add a 120 foot wire paralleled wire so the system > will cover 80, 40, 20 and 15 meters and a pair of 8 foot wires to cover 10 > meters to make it an 80/40/20/15/10 meter system. > > That was a common multi-band antenna before the WARC bands were opened. The > mismatch is much greater on the WARC bands because they are not > harmonically-related to the others. Even though your tuner may produce a > good load to the transmitter, feed line losses can get rather high. > > Ideally you want to fan the wires to the ends are as far apart as possible, > but even several inches or a foot or so will work. > > Understand that a 2:1 or worse SWR is common even though the wires are cut > to 1/2 wavelength due to interaction between them, but the losses should > not > be serious over a typical run of good quality coax. > > 73, Ron AC7AC > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Jerry Weisskohl > Sent: Saturday, December 08, 2012 2:59 PM > To: Mark Bayern > Cc: Elecraft Reflector > Subject: Re: [Elecraft] KAT500 Tuning issue > > Mark, > Thanks for the reply. I received quite a few replies pointing out exactly > what you said. Because it wouldn't load on 20 meters I was using my other > antenna, which works fine with the KAT500 (80 meter vertical). However, I > was trying to understand why the 40 meter dipole wasn't working well on 20 > and I thank all those that replied. This reflector is a wealth of > knowledge! > Now I realize my KAT500 is working as it should. Having two antennas comes > in handy! > > Thanks, > > Jerry - AC4BT > > > On Sat, Dec 8, 2012 at 5:49 PM, Mark Bayern <[email protected]> wrote: > > > Just to make sure we're all on the same page ... > > > > When the tuner (at the radio) gets an acceptable match, that just > > means the transmitter will _think_ there is a good antenna system out > > there. The feedline between the antenna and the tuner will know > > otherwise and can have points of very high voltage that could cause > > insulation breakdown, and points of very high current that can cause > > overheating and will be a source of power loss. This isn't really a > > problem in QRP operations, but when you head into the QRO world it can > > make a difference. The antenna also has issues. In an earlier post > > K3KO had the calculated feedpoint impedance, and it was very far from > > the 'nominal' 50 ohms of your feedline or the ~75 ohms of a dipole at > > altitude. W6GF also gave this info in terms of SWR to show how bad it > > was. All in all a resonant 40M dipole makes an unhappy antenna system > > on 20 meters. > > > > I understand that if that is all you have you're stuck with it, but it > > is really time to consider something else. Maybe a fan dipole, or trap > > dipole? > > > > Mark AD5SS > > > > > > > > On Sat, Dec 8, 2012 at 3:30 PM, Jerry Weisskohl <[email protected]> > > wrote: > > > Right now, I have the coax from the antenna directly connected to > > > the KAT500. I could try using my Delta-4 switch, have the coax go to > > > that and then a small run to the KAT500 to see if that makes a > > > difference. The > > high > > > swr is an issue on 40 and 10 meters, however, ten is manageable, > > > it's > > about > > > 1.9 - 1 and I am working around the issue but using my 80 meter > > > vertical > > on > > > 20 meters. So this is not a "show-stopper" but just wanted to > > > understand why it was happening. > > > > > > Jerry - AC4BT > > > > > > ______________________________________________________________ > 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 > > ______________________________________________________________ > 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 > ______________________________________________________________ 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
