[Elecraft] K2 KAT100 and BL2 questions

[Brian Lloyd]

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