Ok Brian I think I'm getting in step with you. As an example, here I use a 40m dipole, center fed with 450 ohm window line, for 40m, 30m and 20m.
I realized from the beginning that the shack end of the feedline would show a wildly varying impedance, depending on the band. I cut the basic feedline to give me a low impedance with little reactance on 40m. Then I add roughly a quarterwave section on 20m to again give me a low impedance feedpoint for my K2. On 30m, I just use the BL2 balun and set the switch for whichever ratio gives the easiest match for the KAT2 tuner. Again, this doesn't answer your question directly, because I chose to dodge the problem. Using the 4:1 balun at a very high impedance point on the feedline would be pretty lossy, although it would make matching easier for the KAT100. In my case, running only 5w, I felt I didn't have any spare watts to waste :-) Good luck and 73 Bob N6WG ----- Original Message ----- From: "Brian Lloyd" <[EMAIL PROTECTED]> To: "Bob Tellefsen" <[EMAIL PROTECTED]> Cc: <[email protected]> Sent: Monday, June 02, 2008 8:45 PM Subject: Re: [Elecraft] K2 KAT100 and BL2 questions > > On Jun 2, 2008, at 1:32 PM, Bob Tellefsen wrote: > > > Brian > > What are your expectations for this antenna? > > > > Used as a halfwave, say on 40m, its pattern will be that > > of a regular dipole. However, if you feed it at the end, > > it becomes an endfed full wave on 20m. It will not > > have a nice major lobe at right angles to the wire, like > > the dipole. Instead, it will be a four-leafed clover type > > of pattern. > > Yes, I am aware of the various patterns that occur with different > lengths of radiator. That wasn't the question. The questions were > (restated for clarity): > > 1. What is the matching range of the KAT100, i.e. will it match an > antenna fed at a voltage node (multiple of a 1/2 wave) rather than a > current node (odd multiple of a 1/4 wave)? Yes, I know that the > ability to achieve a conjugate match depends on the capacitance and > inductance range of the tuner. Also this affects the range of the real > component (resistance) that can be matched and what frequency you are > trying to match it on. > > 2. Does the BL2 have a problem when looking at a really high > impedance, i.e. when center feeding a full-wave doublet? And yes, I am > aware that I really wouldn't want to feed the balun with coax from the > tuner but rather should put the balun as close to the tuner as > possible and then run a low-loss balanced line from the balun to the > doublet and that the feedline will act as a transformer to change the > impedance (resistance AND reactance) as seen by the balun and, > therefore, the tuner. > > I guess the real question is whether I want to get a KAT100 and a BL2 > or just stick with my SGC-231. The nice thing about the KAT100 is that > it doesn't draw power unless it is tuning. My SGC-231 draws power all > the time to hold in the relays. That sucks up more battery. Also it is > physically bigger. Looking at the schematics for both I can see that > the SGC-231 has a greater range of C and L than the KAT100 does but > maybe the KAT100 is enough, especially when ganged up with the BL2 to > provide a 4:1 impedance ration to start with. I know the theory but > was looking for a quick answer from the field of people here who have > more experience with this than I do. > > > > If you want the pattern on the harmonic band to be at > > right angles to the wire, then you need to center feed it > > with the 450 ohm line. That will give you what is called > > two half waves in phase, with a nice major lobe at right > > angles to the wire and about 2 dB gain over a simple > > dipole. > > Right. I was aware of that. Right now I am primarily interested in > what the limitations of the KAT100 and BL2 are. > > But I appreciate where you are going with this. You are thinking along > the same lines I am but I was still back at the basic mechanics of > matching using the KAT100 and then using the balun to feed the > balanced line irrespective of the radiation pattern. And, yes, end > feeding a 1-wave wire or greater gets you four major lobes. OTOH, take > four of those and put them into a rhombus ... :-) > > > -- > > 73 de Brian, WB6RQN > Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com > > > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
