K2 KAT100 and BL2 questions

[Brian Lloyd-6]

Does anyone know if the KAT100 has enough range to match a radiator  
that is close to (or is) an end-fed 1/2 wave? What I am thinking about  
is feeding a dipole at twice its resonant frequency so that it is  
effectively two end-fed  1/2 wave sections and then feeding with  
ladder line. Now the ladder line will probably act as a transformer to  
change the matching equation. (I know it won't change the SWR but the  
magnitude of the resistance and reactance components will change.)

This also brings up a question I asked much earlier but didn't get a  
good answer to. Will the Elecraft BL2 4:1 balun intended for 300/75  
ohm operation still work properly when feeding the equivalent of two  
end-fed half-wave antennas? If I recall these would represent about an  
8000 ohm impedance. I was thinking of locating the balun very near the  
tuner and using window line to the doublet. I am concerned about  
losses and arcing (100W) in the balun in that specific instance.

--

73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com



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[Don Wilhelm-4]

Brian,

That antenna is commonly referred to as "two half waves in phase" and
has 2 to 3 dB gain broadside to the radiator.

Yes, its feed impedance is high, but if the feedline is somewhere near a
quarterwave (or odd multiple thereof) long at the frequency of interest,
the feedline impedance at the shack end will be low.

A bit of 'playing' with a program like TLW (download for ARRL website)
will indicate what the feedpoint impedance at the shack end might be for
the various bands of interest.

The KAT100 matching range does not usually favor extremely high
impedances, and because the 'delta LC' is fixed, the matching range will
be greater on higher bands than lower ones.  To completely answer your
question, we would need to know the length and type of your feedline and
the band of operation - but I believe I have included enough information
that you can now figure it out for yourself.

73,
Don W3FPR

Brian Lloyd wrote:

> Does anyone know if the KAT100 has enough range to match a radiator
> that is close to (or is) an end-fed 1/2 wave? What I am thinking about
> is feeding a dipole at twice its resonant frequency so that it is
> effectively two end-fed  1/2 wave sections and then feeding with
> ladder line. Now the ladder line will probably act as a transformer to
> change the matching equation. (I know it won't change the SWR but the
> magnitude of the resistance and reactance components will change.)
>
> This also brings up a question I asked much earlier but didn't get a
> good answer to. Will the Elecraft BL2 4:1 balun intended for 300/75
> ohm operation still work properly when feeding the equivalent of two
> end-fed half-wave antennas? If I recall these would represent about an
> 8000 ohm impedance. I was thinking of locating the balun very near the
> tuner and using window line to the doublet. I am concerned about
> losses and arcing (100W) in the balun in that specific instance.
>
> --
>
> 73 de Brian, WB6RQN
> Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
>
>
>
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[John Frerichs]

Has anyone else had trouble with one of the lugs on the DC jack fitting into the smallest hole on the PCB for the N-gen?  I had to trim one solder lug on the jack to make it fit.  Otherwise the ground contact inside the jack would deform from being pushed into the PCB too hard (or risk damage to the PCB if a plug was inserted into the jack prior to mounting it onto the PCB).
   
  After the mod, it fit fine and the the N-gen works perfectly (including being powered from an external source).
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[n6wg]

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.

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.

Good luck and 73
Bob N6WG
The Little Station with Attitude

----- Original Message -----
From: "Brian Lloyd" <[hidden email]>
To: <[hidden email]>
Sent: Monday, June 02, 2008 10:54 AM
Subject: [Elecraft] K2 KAT100 and BL2 questions


> Does anyone know if the KAT100 has enough range to match a radiator
> that is close to (or is) an end-fed 1/2 wave? What I am thinking
about
> is feeding a dipole at twice its resonant frequency so that it is
> effectively two end-fed  1/2 wave sections and then feeding with
> ladder line. Now the ladder line will probably act as a transformer
to
> change the matching equation. (I know it won't change the SWR but
the
> magnitude of the resistance and reactance components will change.)
>
> This also brings up a question I asked much earlier but didn't get a
> good answer to. Will the Elecraft BL2 4:1 balun intended for 300/75
> ohm operation still work properly when feeding the equivalent of two
> end-fed half-wave antennas? If I recall these would represent about
an
> 8000 ohm impedance. I was thinking of locating the balun very near
the

> tuner and using window line to the doublet. I am concerned about
> losses and arcing (100W) in the balun in that specific instance.
>
> --
>
> 73 de Brian, WB6RQN
> Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
>
>
>
> _______________________________________________
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> Post to: [hidden email]
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[Brian Lloyd-6]

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



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[Vic K2VCO]

Brian Lloyd wrote:
>

> 1. What is the matching range of the KAT100, i.e. will it match an
> antenna fed at a voltage node
>
> 2. Does the BL2 have a problem when looking at a really high impedance,
> i.e. when center feeding a full-wave doublet?

Maybe I'm missing something, but the answer depends on the length of the
feedline. If your feedline happens to be an odd multiple of 1/4 wl, then
what the KAT100 and the BL2 will be dealing with will be a very low
impedance, not a high one. A half-wave feedline will repeat the
impedance at the feedpoint. And in-between lengths will give in-between
values.

The balun will operate efficiently as long as the impedance is primarily
resistive and in a range of a few tens to a few hundred ohms. Reactance
is bad for balun efficiency.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Brian Lloyd-6]

On Jun 2, 2008, at 9:25 PM, Vic K2VCO wrote:

> Brian Lloyd wrote:
>
>> 1. What is the matching range of the KAT100, i.e. will it match an  
>> antenna fed at a voltage node 2. Does the BL2 have a problem when  
>> looking at a really high impedance, i.e. when center feeding a full-
>> wave doublet?
>
> Maybe I'm missing something, but the answer depends on the length of  
> the feedline. If your feedline happens to be an odd multiple of 1/4  
> wl, then what the KAT100 and the BL2 will be dealing with will be a  
> very low impedance, not a high one. A half-wave feedline will repeat  
> the impedance at the feedpoint. And in-between lengths will give in-
> between values.

I was aware of that too but still wondering what the worst-case is.  
But I guess the real answer is, if it won't match, add more feedline  
to move around the smith chart and try again. Good point.

> The balun will operate efficiently as long as the impedance is  
> primarily resistive and in a range of a few tens to a few hundred  
> ohms. Reactance is bad for balun efficiency.

Ah. There is the answer I was looking for on the balun. Thank you.

>
> --
> 73,
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco
>

--

73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com



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[n6wg]

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" <[hidden email]>
To: "Bob Tellefsen" <[hidden email]>
Cc: <[hidden email]>
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
>
>
>

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[Pete Connors F5VNB]

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[David Woolley (E.L)]

Brian Lloyd wrote:

> 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.

The ablity to match the real component depends on the imaginary
component.  For a high impedance match, I believe you want the C at the
antenna side.  If you convert 50 ohms in series with the extreme
inductance values (maximum, I think) to the equivalent parallel
combination, at the frequency, you will get the maximum possible real
part transformation.  This might not be achievable for a particular
frequency and antenna reactive component, because of limits in the range
of the C value, it which case you may need to iterate to get an L value
compatible with the limiting C value.

At the extreme limits, the SWR steps will be rather high, so you might
want to consider doing the calculation with an L value that is beyond
the range on the grounds that the resistance match will be no worse than
that halfway between the limit value and the next possible value.

>
> 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.

All current baluns don't like high common mode impedances.  In 4:1 mode,
they also don't like high differential mode impedances.  In both cases,
this is because the leakage inductance reactance is not significantly
higher than that from the relevant feedpoint impedance.  The best place
for a current balun is before the ATU. (A high common mode impedance
with a low differential one is probably not a problem, because most of
the power will go into the differential one; the balun won't help much
but you probably didn't need one.)
>
> 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

The SGC will also have frequency and reactance based variations in its
resistance matching range.  It's balun may well not like high impedances.

> doesn't draw power unless it is tuning. My SGC-231 draws power all the

The KAT2 uses latching relays; the KAT100 uses continuously powered ones.

> 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

That implies operating the balun well away from its design impedance.
Particularly on lower bands, the shunt impedance will be too low.

> for a quick answer from the field of people here who have more
> experience with this than I do.
>

--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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[Don Wilhelm-4]

Pete, Brian and all,

The BL2 *is* a current choke 'balun' - both in the 4:1 and the 1:1
configuration.

73,
Don W3FPR

Peter Connors, F5VNB wrote:

> Brian
>
> Try a current choke 'balun' instead of the BL2.
> As a temporary antenna I have 25m of twin speaker wire run out from
> the shack under the roof tiles - that's about 7m - and then the
> remaining 18m split as a doublet. It hangs at an average height of 5m
> from a couple of trees. The 'feeder' end connects through a current
> choke on a short piece of RG58 to the KAT3 in my K3. The KAT100 has
> the same matching range as the KAT3 and I assume the LC values are the
> similar.
>

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[Pete Connors F5VNB]

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