I have a Comtek 4:1 and a Comtek 1:1 BALUN (from DXEngineering) that I have where I can easily hook up my 450-ohm ladder line to either one.
I have tested both across all the bands that I use on that particular antenna which is 80, 40, and 30. In every case, the Comtek 4:1 gives the better solution as measured by my MFJ 459 antenna analyzer. I do agree that it is not always true that a given 4:1 is better then a 1:1 because on a previous antenna (a delta loop), the 1:1 just so happened to be a little bit better then the 4:1. In all cases though, I measured impedance right from the shack where about 30 feet of coax ran up to the baluns which were mounted outside. On the current antenna, I have close to (but not exactly) 100 feet of 450 ohm ladder line to the antenna feed point. My current antenna is center-fed dipole of about 130 feet in total length. 73, phil, K7PEH On Sep 29, 2012, at 6:40 PM, Don Wilhelm <[email protected]> wrote: > Many hams *asssume* that because the feedline character8istic impedance > is 450 ohms, that it will work better with a 4:1 balun. > > Nothing could be further from the truth, the impedance seen at the shack > end of the feedline can vary from quite high to quite low - the feedline > works as a transmission line tuner (and the ATU does too). > > For powers up to 100 watts, I suggest the Elecraft BL2 which provides a > switch to change from 1:1 to 4:1. Use the setting that provides the > best results. > > 73, > Don W3FPR > > On 9/29/2012 7:41 PM, Adrian wrote: >> Here: >> >> http://www.karinya.net/g3txq/tuner_balun/ >> >> "Amateur Radio (G3TXQ) - Tuner Balun: 4:1 or 1:1 ? >> >> Follow the discussions on any Internet Ham Radio forum and it wont be long >> before someone recommends the use of a 4:1 balun at the output of a tuner >> feeding a multiband doublet through ladderline. Often the recommendation is >> accompanied by an explanation such as: "It helps the tuner to tune" or: "It >> reduces the impedance of the 450 ohm ladderline towards 50Ω". This article >> examines whether the ubiquitous advice to use a 4:1 balun in this scenario >> is valid. >> >> The arguments put forward for a 4:1 impedance transformation often assume >> that the tuner works best when operating with a load impedance close to 50Ω. >> That simply isn't true! The chart on the right shows the losses vs load >> resistance of a typical T-network tuner on 80m for several values of load >> reactance; 80m was chosen because losses tend to be more evident on the >> lower-frequency bands. As we can see the lowest tuner losses occur when the >> load resistance is in the medium/high range 250Ω-2500Ω; the highest losses >> occur at low load resistances, particularly where they are accompanied by a >> large capacitive reactance. >> >> Let's now take the example of a commonly proposed multiband doublet - a >> half-wave 80m dipole fed with 450Ω ladderline. At modest heights above >> average ground the dipole has a feedpoint impedance close to 50Ω. That means >> that the impedance seen at the tuner end of the ladderline could have a >> resistive component anywhere from 50Ω to 4050Ω depending on ladderline >> length; that range of impedances is indicated by the lower shaded bar in the >> chart, labelled 1:1. If we now introduce a 4:1 impedance transformation, the >> range of impedances will be lower by a factor of 4 as indicated by the upper >> shaded bar labelled 4:1. It's clear that the 1:1 range of impedances will >> result in the lower overall losses. >> >> In fact, no matter what the antenna impedance, the range of impedances seen >> at the tuner end of the ladderline would have a "geometric mean" of 450Ω - >> that is they would swing equally below and above 450Ω, but once we introduce >> a 4:1 balun the geometric mean will reduce to 112.5Ω. One look at the loss >> chart tells you that centering the impedances at the higher value is the >> preferable option. >> >> >> Let's now take a look at the specific losses that would occur with our >> example 132 doublet fed with 450Ω ladderline. >> >> The chart on the right was produced by varying the feedline length from 0° >> to 180° in 10° steps. At each step the impedance seen by the tuner was >> calculated both with a 1:1 balun and then with a 4:1 balun, and the tuner >> losses determined using W9CF's T-network tuner simulator. Of course, beyond >> 180° the chart simply repeats itself. Ladderline losses were ignored. >> >> Apart from a small range of line lengths between 80° and 115°, where the >> line has transformed the 50Ω feedpoint impedance to a very high value around >> 4000Ω, the 1:1 balun is the better option; not only that, the worst case >> loss never exceeds 14% with the 1:1 balun whereas it reaches 21% with the >> 4:1 balun. >> >> But what about other bands - the doublet wont be used on just 80m! >> >> >> This chart shows the tuner loss plotted against line length for our example >> doublet on 40m. Here the doublet feedpoint impedance is around 4000Ω, so for >> short ladderline lengths the 4:1 balun shows an advantage. However, as the >> ladderline length increases and the impedance is transformed to lower >> values, the 1:1 balun soon shows the lower losses again. Across the whole >> range of ladderline lengths the 1:1 balun is twice as likely as the 4:1 to >> produce lower losses. >> >> The conclusion seems clear: if you have to choose just one balun, unless you >> know that your combination of doublet/ladderline length falls into the >> minority of cases where a 4:1 balun has the advantage, a 1:1 balun is the >> preferred choice. Add into the mix the fact that most 4:1 baluns are Voltage >> Baluns, whereas to prevent feedline radiation we want balanced currents; >> then consider that all baluns other than a 1:1 Current Balun have the full >> transmit voltage applied common-mode across one or more windings, and the >> case is compelling for a 1:1 Current Balun in this situation. >> >> In this application any small impedance transformation caused by the Current >> Balun is immaterial because the tuner will compensate, so the windings do >> not need to be of any specific characteristic impedance. Typically, bifilar >> windings using Thermaleze wire inserted in Teflon tubes are employed to cope >> with the high differential-mode voltages present at current minima. Balun >> specialists "Balun Designs" offer a nice example in their Model 1171. >> " >> >> -----Original Message----- >> From: Adrian [mailto:[email protected]] >> Sent: Sunday, 30 September 2012 9:34 AM >> To: [email protected] >> Subject: RE: [Elecraft] Balanced solution for KAT500 tuner? >> >> A UK G call did a graphed efficiency comparison test with the 1:1 coming out >> on top. I will post it when re-found. >> >> Also from >> http://www.theladderline.com/doublets-ladder-line-and-automatic-remote-tuner >> s ; (spell-checked) >> >> "There is also some debate about whether the balun should be a 1:1 or 4:1. I >> think 4:1 has been quite popular in the past. This perhaps comes from the >> thought that the ladder line is higher impedance than coax so we need to >> step down to get it closer to the coax impedance. On the forums, people who >> have modelled the antenna with software like EZNEC seem to make a fairly >> compelling argument that a 1:1 balun is more likely to present an impedance >> within the range of the tuner over a wide range of frequencies. The >> impedance will depend on the length of the ladder line so it's a bit of a >> gamble but I'm getting good results from a 1:1 current balun. >> >> After doing some reading and playing with a home brew balun, I finally took >> the lazy way out and splashed out on a serious balun. It's a DX Engineering >> BAL050-H10-AT. It's not cheap but I think it was a good investment. I don't >> have any hard evidence to show how good it is compared to a cheaper balun >> but I have a feeling that it contributes to the good performance I get with >> this antenna. I've had absolutely no "RF in the shack" or similar problems >> even at the old QTH when I had the ladder line coming into the shack. >> >> An interesting fact that I learned from the forums is the reason ladder line >> works more successfully than coax in a multiband situation like this. The >> common belief is that ladder line "doesn't care" about high SWR. It's true >> that ladder line usually has lower loss than coax at a given SWR but that's >> not the whole story. Another rather simple factor is that the characteristic >> impedance of ladder line is higher than coax so therefore, for a typical >> wire antenna over a wide range of frequency, the average SWR on ladder line >> tends to be lower than it would be with coax and that helps keep the loss >> low." >> >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of David Gilbert >> Sent: Sunday, 30 September 2012 8:37 AM >> To: [email protected] >> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >> >> >> I don't believe that is necessarily true. Can you cite a reference to back >> up that statement? Or at least describe in physical terms (Q, currents, >> voltages, component loss, etc) why that would be so? I'm honestly curious >> what the difference would be. >> >> 73, >> Dave AB7E >> >> >> >> On 9/29/2012 2:13 PM, Adrian wrote: >>> 1:1 current balun has proven more efficient in conjunction with the >>> appropriate balanced (matchbox style)tuner. >>> >>> -----Original Message----- >>> From: [email protected] >>> [mailto:[email protected]] On Behalf Of Robert G. >>> Strickland >>> Sent: Sunday, 30 September 2012 4:26 AM >>> To: [email protected] >>> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >>> >>> Jim... >>> >>> Is there anything to be gained in putting a 1:1 "balanced isolator" at >>> the feed point of an antenna that is fed by a "parallel wire" feed >>> line? Does such an arrangement achieve feed line isolation while >>> preserving the ability of such an antenna to be driven on various >>> bands other than its resonant frequency? Thanks for your input. >>> >>> ...robert >>> >> ______________________________________________________________ >> 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 ______________________________________________________________ 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
