[Elecraft] K2 KAT100 and BL2 questions

[Bob Tellefsen]

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" <brian-wb6rqn at lloyd.com>
To: "Bob Tellefsen" <n6wg at comcast.net>
Cc: <elecraft at mailman.qth.net>
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
>
>
>