[Elecraft] K2, KAT2 and displaced choke balun feed

[Roelof Bakker]

Hello all,

I have just finished K2 # 6177 and with all HF bands to my disposal, I am
looking for a more convenient way to feed my doublet wire antenna with open
feeder. My shack is in the dining room (my wife is very forgiving) and the
antenna feed-in is on the window sil at the opposite side of the room. Hence
I use 6 metre coax to get there.

Has anyone tried a K2 and KAT2 fed into a substantial length of 50 ohm coax
with a choke balun mounted at the other end, connected to an open line
feeder? So far I have used a manual balanced tuner on the window sil, but
that implies getting up and walking to the tuner when changing bands.

Thank you in advance,

Roelof Bakker, pa0rdt
G-QRP-C 6019
QRP-ARCI 8405
Middelburg, Netherlands
JO11tm

[Robie Elms]

Roelof,

I have used the arrangment you are asking about several times and it has
worked well for me. One key point is that baluns are not effective under
some load conditions, usually when they are transforming high
impedence/highly reactive loads. So if you encounter problems matching
the antenna on some bands you can "adjust" the load that the balun sees
(from the antenna) by adding a short piece of transmission line between the
balun and the antenna. This technique uses transmission line properties to
"transform" the impedence to a value that the balun is more capable of
handling. You may find that you need to add a piece to you transmission
line on one or two bands. The specific lengths depend on your specific
installation. The ARRL Antenna Book is a good place to learn about
transmission line properties and how to use them. There are many other
sources of this information as well.

I hope this information helps.

Robie - AJ4F



----- Original Message -----
From: "Roelof Bakker" <***@ndb.demon.nl>
To: <***@mailman.qth.net>
Sent: Wednesday, August 15, 2007 8:44 AM
Subject: [Elecraft] K2, KAT2 and displaced choke balun feed

Post by Roelof Bakker
Hello all,
I have just finished K2 # 6177 and with all HF bands to my disposal, I am
looking for a more convenient way to feed my doublet wire antenna with
open feeder. My shack is in the dining room (my wife is very forgiving)
and the antenna feed-in is on the window sil at the opposite side of the
room. Hence I use 6 metre coax to get there.
Has anyone tried a K2 and KAT2 fed into a substantial length of 50 ohm coax
with a choke balun mounted at the other end, connected to an open line
feeder? So far I have used a manual balanced tuner on the window sil, but
that implies getting up and walking to the tuner when changing bands.
Thank you in advance,
Roelof Bakker, pa0rdt
G-QRP-C 6019
QRP-ARCI 8405
Middelburg, Netherlands
JO11tm
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[Brett gazdzinski]

I have a homebrew G5RV, about 105 feet long, up 40 feet, fed with
home made open wire line (#12 wire), into about 25 feet of RG214,
then to the station control (multi antenna's, transmitters, receivers,etc.)
and into the K2. No baluns.

The tuner tunes it great on all bands, highest swr is 1.3:1.

I don't have the 160 meter option, might not work on that...

Brett
N2DTS

-----Original Message-----
Sent: Wednesday, August 15, 2007 9:44 AM
Subject: [Elecraft] K2, KAT2 and displaced choke balun feed
Hello all,
I have just finished K2 # 6177 and with all HF bands to my
disposal, I am
looking for a more convenient way to feed my doublet wire
antenna with open
feeder. My shack is in the dining room (my wife is very
forgiving) and the
antenna feed-in is on the window sil at the opposite side of
the room. Hence
I use 6 metre coax to get there.
Has anyone tried a K2 and KAT2 fed into a substantial length
of 50 ohm coax
with a choke balun mounted at the other end, connected to an open line
feeder? So far I have used a manual balanced tuner on the
window sil, but
that implies getting up and walking to the tuner when changing bands.
Thank you in advance,
Roelof Bakker, pa0rdt
G-QRP-C 6019
QRP-ARCI 8405
Middelburg, Netherlands
JO11tm
--
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[Roelof Bakker]

Hello Brettet al,

Thank you all for the information.
I am considering a manual balanced tuner and a KAT2 and a choke balun.
Measuring the feeder current should reveal if there is any difference.

73,
Roelof Bakker, pa0rdt
G-QRP-C 6019
QRP-ARCI 8405
Middelburg, Netherlands
JO11tm

[Roelof Bakker]

Hello all,

A few weeks ago I asked for advice on the use of the KAT2 feeding a length
of coax, followed by a balun connected to the balanced feeder of my doublet.
In my case 15 metre of coax is needed between the K2 and the balun/open wire
feeders.
Quite a few people seem to have a similar situation and are happy with the
KAT2 and balun.

I used the program dipole3.exe from the late G4FGQ to run a simulation on
several bands. From 80 to 10 m the efficiency was about 50 - 60 procent,
which is not really bad.
However it is not very good either and I decided to try a balanced tuner,
before installing a KAT2 (which I will eventually). I purchased a MFJ 974HB
and though I did not have very high expectations of it, I was pleasantly
surprised. It matches the doublet fine, but that is not the point. The
balance seems to be excellent as most of my local noise is now gone,
compared to using a 1:4 balun. Even the LAN crud on 14.030 MHz is almost
gone.
This complies with earlier findings that at my location the better part of
local noise is contained inside the houses.

The centre of the antenna is mounted on a 5 metre long fibre glass pole,
dropping to 1.5 metre at the ends. It runs above the semi-flat roof of a
block of 5 houses. I live in the middle one.

When the balance is less than perfect common mode noise is introduced in the
system.
The difference is amazing; on 80 I can listen again to the band noise going
up and down as waves on the seashore.

Though this works for me at the moment, it should be nice if someone
(Elecraft?) could come up with a stand alone truely balanced automatic
antenna tuner.

73,
Roelof Bakker, pa0rdt
Middelburg, Netherlands
JO11tm

[Lamb, Dick &amp; Judy]

I had exactly the same experience as Roel and reached the same
conclusions. I agree that a commercial BALANCED autotuner would be
the best solution for an all-band dipole, if there were such a thing.

Like Roel, I attempted to use a KAT2 and balun arrangement for all-
band feeding of a simple dipole at the center with open wire line. I
put the balun right at the output of the KAT2--no coax at all.
However, both with actual measurements and with simulations using
dipole3.exe, I could find no combination of feedline length and
antenna length for my QTH that would present an acceptable match for
the balun (either 1:1 or 4:1) on all bands. High reactance was
usually the problem, although in some cases the overall impedance was
too high for the tuner. With the best of compromises, I determined
from measurements that on some bands about half of my power was
heating the balun. True, that's only 3 db, about half an S unit.
However, it's like degrading my KPA100 to 50 watts, and not many of
use would accept that. The KAT2 alone, with balanced lines connected
to the SO239 and ground, didn't have sufficient range to match some
bands, and the balance was terrible on others. Maybe I'm
overlooking something, and I'd sure appreciate a response from
someone with difference experience or more knowledge.

Before getting my KAT2 I used a link-coupled tuner I'd built, and it
would match anything with high efficiency and excellent balance. But
band changing with plug-in coils was a pain. Then, like Roel, I
acquired an MFJ-974H balanced tuner, and I am also most pleased with
the results. I built a twin current meter to measure balance in the
feedline, and balance and efficiency is as good with the MFJ tuner as
with my link-couple tuner. I can tune the MFJ tuner for a new band
in a few seconds from a chart of settings I developed. Also, I keep
a noise bridge in the antenna line, with capability to switch it in
when I want it, and that will allow a quick fine tuning (a couple
seconds, usually) without transmitting on the air.

However, it would be so nice to have a wide-range balanced
autotuner. I couldn't find one on the amateur market.

Dick, K0KK

I purchased a MFJ 974HB and though I did not have very high
expectations of it, I was pleasantly surprised. It matches the
doublet fine, but that is not the point. The balance seems to be
excellent as most of my local noise is now gone, compared to using
a 1:4 balun.
Though this works for me at the moment, it should be nice if
someone (Elecraft?) could come up with a stand alone truely
balanced automatic antenna tuner.
73,
Roelof Bakker, pa0rdt
Middelburg, Netherlands
JO11tm
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[Vic K2VCO]

Post by Lamb, Dick &amp; Judy
I had exactly the same experience as Roel and reached the same
conclusions. I agree that a commercial BALANCED autotuner would be the
best solution for an all-band dipole, if there were such a thing.

Oh, there is all right. It's just a bit expensive!

<http://www.hamware.de/hardware/tuner502/at502-e.htm>

[Don Ehrlich]

I had to design and build my own because I wanted to run up to a KW through
it. If I had to buy new matched roller inductors they alone would cost over
400 dollars.

I found most of what I needed in my junkbox or on Ebay but even so the parts
and materials alone were well over 300 dollars ... and I laid out and built
my own circuit board, bent my own aluminum, and made many component
compromises. Any commercially built balanced autotuner for a KW would be
*very* expensive. Many hundreds of man-hours later for construction and
software programming have finally got me what I wanted and I am very happy
with it. But I don't ever expect to see one on the market that is easily
affordable for most hams.

Don K7FJ

-----------------------------------------

However, it would be so nice to have a wide-range balanced autotuner. I
couldn't find one on the amateur market.

Though this works for me at the moment, it should be nice if someone
(Elecraft?) could come up with a stand alone truely balanced automatic
antenna tuner.
73,
Roelof Bakker, pa0rdt
Middelburg, Netherlands
JO11tm

[Brett gazdzinski]

I have been thinking of doing the same thing, but good for
600 watts of AM carrier plus modulation.
I would wind the coils out of copper tubing, and make the coils
tapped with a switch, only the best roller inductors hold up
over time.
The coils would have a link input from the rig side.

http://www.cebik.com/link/link.html


Sort of like the old Johnson matchboxes.

They also had a switch instead of a roller inductor, the roller
allows too wide a range, its sometimes hard to repeat
settings as there are to many variables.

I have a heathkit tuner now with the roller inductor, and its
a real pain, a switch for the band would be better, even though
the match might be slightly off.

Brett
N2DTS

-----Original Message-----
Sent: Thursday, September 06, 2007 6:05 PM
To: Lamb, Dick & Judy; Roelof Bakker
Subject: Re: [Elecraft] K2, KAT2 and displaced choke balun feed
I had to design and build my own because I wanted to run up
to a KW through
it. If I had to buy new matched roller inductors they alone
would cost over
400 dollars.
I found most of what I needed in my junkbox or on Ebay but
even so the parts
and materials alone were well over 300 dollars ... and I laid
out and built
my own circuit board, bent my own aluminum, and made many component
compromises. Any commercially built balanced autotuner for
a KW would be
*very* expensive. Many hundreds of man-hours later for
construction and
software programming have finally got me what I wanted and I
am very happy
with it. But I don't ever expect to see one on the market
that is easily
affordable for most hams.
Don K7FJ
-----------------------------------------

Post by Lamb, Dick &amp; Judy
However, it would be so nice to have a wide-range balanced

autotuner. I

Post by Lamb, Dick &amp; Judy
couldn't find one on the amateur market.

Post by Roelof Bakker
Though this works for me at the moment, it should be nice

if someone

Post by Lamb, Dick &amp; Judy

Post by Roelof Bakker
(Elecraft?) could come up with a stand alone truely

balanced automatic

Post by Lamb, Dick &amp; Judy

Post by Roelof Bakker
antenna tuner.
73,
Roelof Bakker, pa0rdt
Middelburg, Netherlands
JO11tm

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[Don Wilhelm]

Dick,

Warning, a bit of theory talk follows:

I believe your post combined two different aspects of tuners. Matching
range limitations are a fact of life with any tuner design whether
auto-tuner or manual and whether a balanced tuner or an unbalanced tuner.
In my attic I do have an old homebrew, link coupled, tapped plug-in coil
tuner that I can use to match most any load that I can through at it -
it has straps to configure it for series tuning if the impedence is low
and when configured for parallel tuning, will match a very high
impedance. BUT, it is not very good at bandswitching, and if I change
the antenna, I have to set things up again. Those were the 'good old
days' and it worked very well when I was confined to one or two antennas.

As far as balance from a balun output goes, theoretically the output
should be very well balanced if the balun is a proper balun. If you do
not have good balance from a balun, I believe you really should be
asking how your installation differs substantially from the theoretical
model of a balun and solve the problem at its source.

With a good balun at the output of a good unbalanced autotuner, the
balance *should* be perfect. The task of finding out why it may not be
perfect in any one installation may indeed be more difficult than giving
up and simply using a modern balanced tuner even with the drawbacks of
any of the currently available balanced tuners.

For myself, I choose the easy solution for portable operation - the KAT2
followed by a balun works great for me, and at home I have all resonant
antennas so a tuner is not required except for a minor 'touch-up' on the
high end of 75 meters (and I don't operate there very often), so an
unbalanced tuner works fine for my applications.

73,
Don W3FPR

Post by Lamb, Dick &amp; Judy
I had exactly the same experience as Roel and reached the same
conclusions. I agree that a commercial BALANCED autotuner would be
the best solution for an all-band dipole, if there were such a thing.
snip...

[Jim Brown]

Post by Roelof Bakker
When the balance is less than perfect common mode noise is introduced
in the system. The difference is amazing;

Yes, it is. But there is a FAR easier way to achieve that with plain
ordinary coax and a good common mode choke formed by winding the coax
around suitable ferrite cores.

http://audiosystemsgroup.com/RFI-Ham.pdf

See the section on transmitting chokes and the "Choke Cookbook."

73,

Jim Brown K9YC

[N2EY at aol.com ()]

In a message dated 9/6/07 6:07:54 PM Eastern Daylight Time,

Post by Don Wilhelm
With a good balun at the output of a good unbalanced autotuner, the
balance *should* be perfect. The task of finding out why it may not be
perfect in any one installation may indeed be more difficult than giving
up and simply using a modern balanced tuner even with the drawbacks of
any of the currently available balanced tuners.

One big reason for unbalance is the wide variety of impedances that the
balanced load may present. What balun can do its job with resistive part varying
from a few ohms to several thousand, and reactive part from a few thousand
capacitive to a few thousand inductive? And do the job over a 10:1 HF frequency
range?

This is why the unbalanced tuner/balun combo works so well for some and so
poorly for others - or even both, depending on band. If the impedance and
frequency to be matched are such that the balun can do its job, great! But that's
not always the case.

73 de Jim, N2EY


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