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KAT500 update

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Ignacy

Re: KAT500 update

Imagine choke constructed with RG174 looped through a toroid 10 times. Also imagine output resitstance 2500 Ohms and 100W power.

On input, RG174 has a peak voltage of 100V. No problem.

On output, RG174 has a peak voltage of 1000V. It would melt in seconds.

What is wrong here? Assumptions?

Ignacy

Jim AB3CV

Re: KAT500 update

On a previous post I included three links which if read would lead you to
the conclusion that a common choke on the output of the "unbalanced" tuner
of sufficient impedence would ensure that all of the current on the
interior of the shield of the coax and on the center conductor would be
present on the "balanced" line if the outside of the shield was prevented
from carrying RF.

That equal and opposite current present on the "balanced" line is what is
desired.

No transformer, balun, etc which would be suject to widely varying
impedences from such a line is required.

Just squirt the current in equal and opposite amounts and don't let it leak
anywhere.... <-technical description...

jim ab3cv
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Don Wilhelm-4

Re: KAT500 update

In reply to this post by Don Wilhelm-4

Ron,

Yes, that is valid justification for putting the balun at the tuner
input, BUT it ignores the physics of the tuner itself. If the tuner is
actually a balanced design, I have no problem, but many try to force fit
an unbalanced tuner design after the balun. That latter part is the
part that does not fit. There is no way that an unbalanced network no
matter how well isolated can preserve the balance - just consider the
phase of the signal as it passes through each tuner element if you want
proof.

If you want to use a balun at the tuner input, then please follow it
with a balanced tuner t maintain that balance.

If you want to use the "rule of thumb" that the balun impedance should
be 10 times the load impedance, then refer to K9AY's RFI and balun
information and use those 5 or 6 large cores to provide the proper
choking impedance for up to 500 ohms antenna impedance (5000 ohms
impedance for the balun).

73,
Don W3FPR

On 12/8/2011 7:36 PM, Ron D'Eau Claire wrote:

> Is it true that the efficiency of a balun is not affected by the impedance
> of the line in which it is used?
>
> The justification I had seen for putting the balun at the tuner input where
> it will see a load very close to 50 ohms resistive (when the tuner is
> adjusted for a "match") while at the output the balun may see anything over
> a huge range of impedances.
>
> Ron AC7AC
>
>

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KEN-3

Re: KAT500 update

In reply to this post by Jim Brown-10

On Dec 8, 2011, at 6:47 PM, Jim Brown wrote:

> Virtually all the loss in transmission lines at HF (and even VHF) is due
> to copper (that is, I squared R). Open wire line (and window line) has
> much lower loss than coax because it has much higher impedance, so the
> current for the same transmit power is much less than for coax.

The impedance of the feedline does not change the impedance of the antenna. A half wave length dipole at the proper height is still a 50 ohm feed regardless of whether it's fed with 50ohm line or 600 ohm line.

Ken WA8JXM

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Ignacy

Re: KAT500 update

W8JI and other sites assume that the balun is lossless except for common mode. Also that voltage breakage is unimportant. Both are good approximations when the balun is large and wound by thick wire or with teflon cable.

Assume we use RG174 for windings. We have SWR 1:1 on input and 25:1 with 2500 Ohm input. Thus 25 lower power ratings on output than on input. Could be 100W max with balun on on input and 4 W max with balun on output.

One can always substitute a bigger coax (increase the balun size a few times), or use bifilar windings (and worrying about insulation breakage). Summarizing, a $2 balun on input would be as effective as a $50 balun on output, and 10 times lighter. Not important for stationary equipment but important when portable.

For KAT500 its is better to use a $50 balun as otherwise switching would cost more.

Perhaps this thread is no longer relevant to KAT500 and needs to be terminated.

Ignacy

Don Wilhelm-4

Re: KAT500 update

In reply to this post by KEN-3

Ken,

Actually, the feedpoint impedance for a half wave center fed dipole is
70 ohms if it is "in the clear". The proximity to earth and other
physical objects will lower that impedance. For antennas typically used
at HF, yes, the feedpoint impedance will be closer to 50 ohms than the
ideal of 70 ohms.

73,
Don W3FPR

On 12/8/2011 8:14 PM, Ken wrote:

> On Dec 8, 2011, at 6:47 PM, Jim Brown wrote:
>
>> Virtually all the loss in transmission lines at HF (and even VHF) is due
>> to copper (that is, I squared R). Open wire line (and window line) has
>> much lower loss than coax because it has much higher impedance, so the
>> current for the same transmit power is much less than for coax.
>
> The impedance of the feedline does not change the impedance of the antenna. A half wave length dipole at the proper height is still a 50 ohm feed regardless of whether it's fed with 50ohm line or 600 ohm line.
>
> Ken WA8JXM
>
>
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KEN-3

Re: KAT500 update

Don,

Yes, I know, that's why I said "at the proper height".

73, Ken WA8JXM

On Dec 8, 2011, at 8:49 PM, Don Wilhelm wrote:

> Ken,
>
> Actually, the feedpoint impedance for a half wave center fed dipole is 70 ohms if it is "in the clear". The proximity to earth and other physical objects will lower that impedance. For antennas typically used at HF, yes, the feedpoint impedance will be closer to 50 ohms than the ideal of 70 ohms.
>
> 73,
> Don W3FPR
>
> On 12/8/2011 8:14 PM, Ken wrote:
>> On Dec 8, 2011, at 6:47 PM, Jim Brown wrote:
>>
>>> Virtually all the loss in transmission lines at HF (and even VHF) is due
>>> to copper (that is, I squared R). Open wire line (and window line) has
>>> much lower loss than coax because it has much higher impedance, so the
>>> current for the same transmit power is much less than for coax.
>>
>> The impedance of the feedline does not change the impedance of the antenna. A half wave length dipole at the proper height is still a 50 ohm feed regardless of whether it's fed with 50ohm line or 600 ohm line.
>>
>> Ken WA8JXM
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
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Don Wilhelm-4

Re: KAT500 update

In reply to this post by Eric Swartz - WA6HHQ

I read the W8JI comments presented in that link on the Elecraft website.
I was familiar with Tom's work and comments from emailing with him on
this particular subject many years ago.

The one thing that struck me in W8JI's paper is at the end and embodied
in Tom's comment that --

"The irony is, moving the balun to the input mostly works only when the
balun is not needed!"

For those who want a really high efficiency balanced tuner, go to ARRL
publications back several years to find a link coupled tuner. With
switching between series and parallel tuning, it can handle impedances
from very low to very high. The input is DC isolated from the output,
and the input can be either unbalanced or balanced. The output can be
either balanced or unbalanced depending on where you connect the output
tuned circuit. The venerable Johnson Matchbox is an example of a link
coupled tuner. The taps onto the output tank circuit were created by
the differential capacitor in the output tank circuit - that allowed it
to be boxed up into a bandswitchable box without need for connecting the
antenna feeders to taps on the tuner coil. That works quite well , but
it restricts the range of matching impedances to significantly less than
would be obtained by the basic tuner with taps on the inductor. Yes, I
do use these tuners, and they are configured for single band use at the
antenna - 3 coax feeds for HF and 3 for VHF/UHF give me access to all my
antennas The nearest antenna is 200 feet of coax away from the
hamshack, and that is why I use tower mounted preamps for VHF/UHF.

I will never give up my Matchbox until it is pried from my cold dead
hands - I use mine mostly as a test instrument - as bandpass filter as
well as an impedance transformation device. After experimentation asnd
development, the permanent tuners are designed and installed in the
antenna field - I have tuned coax fed antennas for each band from 160
meters through the 432 MHz bands. I use the Matchbox tuner only for
experimental antennas until I can develop a permanent and dedicated
tuner for any one antenna.

OK, those are the advantages - the drawbacks are that that the link
coupled tuner arrangement does not lend itself well to bandswitching,
but i would suggest it be the tuner of choice for situations where the
antenna is used for only a single band - put the tuner on the antenna
feedline and tune it to resonance (and minimum SWR) once and be done
with the settings.

73,

Don W3FPR

On 12/8/2011 6:28 PM, Eric Swartz - WA6HHQ, Elecraft wrote:

> Hi Ignacy,
>
> This is a common misconception. (One which I held until recently. :-) It
> turns out there is no advantage to placing the balun at the input of the
> L-Network tuner. Since one end of the balun is grounded by the input to
> the tuner, it is still presented with the same stresses under high SWR
> situations. Baluns at the input and output both drive balanced loads
> equally well.
>
> We've now put together a web page describing the impact of placing the
> balun at the input or at the output of a L-Network tuner. See:
>
> http://www.elecraft.com/KAT500/input_versus_output_balun.htm
>
>

Jim AB3CV

Re: KAT500 update

In reply to this post by Jim AB3CV

The links I provided show how to do just that including test data to back
it up. Google "k9yc", "w9cf"

jim ab3cv
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Alan Bloom

Balun on tuner input?

In reply to this post by Don Wilhelm-4

There's a simple way to look at this that requires no high-level math or
complicated analysis.
_________ _________
I1 --> | | | | I3 -->
--------| |--| |-------
Transmitter | BALUN | | TUNER | Antenna
--------| |--| |-------
I2 --> |_________| |_________| I4 -->

The purpose of the balun is to eliminate the common-mode current. The
CM current is the NET current, that is, I1 + I2 at the input and I3 + I4
at the output. The balun does not store electrons, so it must be that:

Input common-mode current = output common-mode current.

That is true for both the balun and the tuner. No matter whether the
balun is on the transmitter or antenna side of the tuner it does an
equally good (or bad) job of choking the common-mode currents.

The advantage of putting the balun at the input is that the
differential-mode voltages and currents (the ones you want) are
well-controlled because of the constant 50-ohm impedance. The DM
current or voltage at the output can be much higher, depending on the
load impedance. Of course, the common-mode current and voltage are the
same at the input and output, but even so the worst-case stress on the
balun should be less when it is at the input.

The disadvantage of putting the balun at the input is that none of the
tuner circuitry can be grounded. For example, the control shafts of the
variable capacitors have RF voltage on them, so the knobs must be
isolated. If it is an automatic antenna tuner, that is less of a
problem.

Bottom line? The ARRL is not necessarily "wrong" to put the balun at
the tuner input. It's just a matter of whether you think the lower
worst-case current/voltage on the balun is worth the hassle of floating
the tuner ground.

Alan N1AL

On Thu, 2011-12-08 at 18:59 -0500, Don Wilhelm wrote:

> This is of interest to me, because in my first experiences with antenna
> forums (or was it newsgroups at the time), I recall a lot of exchanges
> with Tom W8JI on exactly the "balun at the tuner input and isolated
> unbalanced tuner". I concur with Tom - it does not work -- both from a
> theoretical basis, and also from Tom's measurements.
>
> This was "way back when" - as I recall my situation when all this was
> going on, I was running Windows 95 and the year was between 1997 and 1998.
>
> In the timeframe of this discussion, Zack Lau (ARRL engineer) who had
> first published the "balun at the tuner input" concept as a QRP tuner,
> had retracted that design because it did not maintain balance, but Dean
> Straw (ARRL engineer, editor, etc.) published his design of a high power
> tuner using the same concepts, and that design can still be seen in the
> ARRL publications.
>
> Apologies for the comments into the politics of the ARRL decisions on
> what is to be published, but that is both a bit of the history as I know
> it as well as my view of the technical side of this issue.
>
> If anyone can tell me how you can run a signal through a balun - and
> have equal and opposite currents at its output, and then run it through
> an unbalanced network with unequal elements in the two series legs and
> still maintain equal and opposite currents and phase, and I will then
> concede that an isolated unbalanced tuner with a balun at the input will
> work, but until that is presented to me along with detailed engineering
> level test data (not just "it works"), I will continue to believe that
> using a balun on the input of an isolated unbalanced tuner is a "pipe
> dream" that does not mesh with reality.
>
> 73,
> Don W3FPR
>
> aOn 12/8/2011 6:28 PM, Eric Swartz - WA6HHQ, Elecraft wrote:
> > Hi Ignacy,
> >
> > This is a common misconception. (One which I held until recently. :-) It
> > turns out there is no advantage to placing the balun at the input of the
> > L-Network tuner. Since one end of the balun is grounded by the input to
> > the tuner, it is still presented with the same stresses under high SWR
> > situations. Baluns at the input and output both drive balanced loads
> > equally well.
> >
> > We've now put together a web page describing the impact of placing the
> > balun at the input or at the output of a L-Network tuner. See:
> >
> > http://www.elecraft.com/KAT500/input_versus_output_balun.htm
> >
> > At the bottom of that page are several links providing detailed
> > technical analysis of these configurations. The first two, by W8JI and
> > W7EL are very clear discussions of this issue.
> >
> > 73, Eric WA6HHQ
> >
> > www.elecraft.com
> >
> >
> > On 12/8/2011 3:17 PM, Ignacy wrote:
> >> It seems to me that the story is more complex than it sounds.
> >>
> >> The input balun always works at low SWR and at 50 Ohm. It is very easy to
> >> have such balun. A small balun would easily handle a KW without heating.
> > ______________________________________________________________

Dave-7

Re: KAT500 update

In reply to this post by Don Wilhelm-4

Don't forget that MFJ now makes a balanced tuner. Three versions -
974B, 974HB, 976. They do have what is needed - a balun at the input
followed by a fully balanced tuner. Or at least they appear to be
fully balanced.

73 de dave
ab9ca/4

On 12/8/11 8:53 PM, Don Wilhelm wrote:

>
> I read the W8JI comments presented in that link on the Elecraft website.
> I was familiar with Tom's work and comments from emailing with him on
> this particular subject many years ago.
>
> The one thing that struck me in W8JI's paper is at the end and embodied
> in Tom's comment that --
>
> "The irony is, moving the balun to the input mostly works only when the
> balun is not needed!"
>
> For those who want a really high efficiency balanced tuner, go to ARRL
> publications back several years to find a link coupled tuner. With
> switching between series and parallel tuning, it can handle impedances
> from very low to very high. The input is DC isolated from the output,
> and the input can be either unbalanced or balanced. The output can be
> either balanced or unbalanced depending on where you connect the output
> tuned circuit. The venerable Johnson Matchbox is an example of a link
> coupled tuner. The taps onto the output tank circuit were created by
> the differential capacitor in the output tank circuit - that allowed it
> to be boxed up into a bandswitchable box without need for connecting the
> antenna feeders to taps on the tuner coil. That works quite well , but
> it restricts the range of matching impedances to significantly less than
> would be obtained by the basic tuner with taps on the inductor. Yes, I
> do use these tuners, and they are configured for single band use at the
> antenna - 3 coax feeds for HF and 3 for VHF/UHF give me access to all my
> antennas The nearest antenna is 200 feet of coax away from the
> hamshack, and that is why I use tower mounted preamps for VHF/UHF.
>
> I will never give up my Matchbox until it is pried from my cold dead
> hands - I use mine mostly as a test instrument - as bandpass filter as
> well as an impedance transformation device. After experimentation asnd
> development, the permanent tuners are designed and installed in the
> antenna field - I have tuned coax fed antennas for each band from 160
> meters through the 432 MHz bands. I use the Matchbox tuner only for
> experimental antennas until I can develop a permanent and dedicated
> tuner for any one antenna.
>
> OK, those are the advantages - the drawbacks are that that the link
> coupled tuner arrangement does not lend itself well to bandswitching,
> but i would suggest it be the tuner of choice for situations where the
> antenna is used for only a single band - put the tuner on the antenna
> feedline and tune it to resonance (and minimum SWR) once and be done
> with the settings.
>
> 73,
>
> Don W3FPR
>
> On 12/8/2011 6:28 PM, Eric Swartz - WA6HHQ, Elecraft wrote:
>> Hi Ignacy,
>>
>> This is a common misconception. (One which I held until recently. :-) It
>> turns out there is no advantage to placing the balun at the input of the
>> L-Network tuner. Since one end of the balun is grounded by the input to
>> the tuner, it is still presented with the same stresses under high SWR
>> situations. Baluns at the input and output both drive balanced loads
>> equally well.
>>
>> We've now put together a web page describing the impact of placing the
>> balun at the input or at the output of a L-Network tuner. See:
>>
>> http://www.elecraft.com/KAT500/input_versus_output_balun.htm
>>
>>
> ______________________________________________________________
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Bob Cunnings NW8L

Re: KAT500 update

In reply to this post by wayne burdick

Another available tuner is the Palstar BT1500A, a balanced L tuner
with choke balun at input. I've been using one for years here. Build
quality is excellent and it has served me well matching doublets fed
by 450 ohm window line running into the shack. Right now it's being
used with the KPA500.

Bob NW8L

>Don't forget that MFJ now makes a balanced tuner. Three versions -
>974B, 974HB, 976. They do have what is needed - a balun at the input
>followed by a fully balanced tuner. Or at least they appear to be
>fully balanced.
>
>
>73 de dave
>ab9ca/4
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Jim Brown-10

Re: KAT500 update

In reply to this post by Don Wilhelm-4

First we must define what sort of "balun" we are talking about. I know
of a half dozen different devices/circuit elements that are commonly
called baluns, and most are very different from each other. I abhor the
word "balun," and try to avoid using it. I have done considerable
research, and published what I've learned, on the subject of COMMON MODE
CHOKES wound on ferrite cores, especially LOSSY ferrite cores. The
efficiency of such a common mode choke is essentially independent of the
SWR, except to the extent of the increased loss in the short length of
transmission line wound through the core to form the choke.

Since I have no idea what sort of "balun" Elecraft plans for their
tuner, I have no comments on it. I have, however, measured some common
mode chokes bifilar wound using #14 and #12 THHN to form a parallel wire
transmission line that have excellent choking performance for the HF
bands. The data are included in the latest version of my RFI tutorial
(since the summer of 2010).

The concept of a totally isolated tuner with common mode chokes at input
and output is so non-nonsensical to me that I've never contemplated it.
It is also nonsense to consider parallel wire line as a balanced system
unless everything connected to it is also balanced -- that is, tuner,
line, and antenna. Since most ham antennas are at least somewhat
unbalanced by their surroundings, even when fed by these parallel wire
lines, there will be SOME imbalance in the line, and thus some common
mode current. That common mode current causes trouble in at least three
ways -- it puts RF in the shack to excite Pin One Problems (very common
in ham gear); the common mode current will radiate, potentially causing
RFI to consumer gear in your living room (and your neighbor's); and by
reciprocity, the transmission line will act as a receiving antenna,
coupling noise from your neighbor's computers and battery chargers to
your receiver. THAT"S why we need common mode chokes at the feedpoint
of EVERY antenna, whether fed with coax or parallel wire line.

Loss in common mode chokes is addressed in the sections of my RFI
tutorial where transmitting chokes are discussed.

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

73, Jim Brown K9YC

On 12/8/2011 4:36 PM, Ron D'Eau Claire wrote:
> Is it true that the efficiency of a balun is not affected by the impedance
> of the line in which it is used?
>
> The justification I had seen for putting the balun at the tuner input where
> it will see a load very close to 50 ohms resistive (when the tuner is
> adjusted for a "match") while at the output the balun may see anything over
> a huge range of impedances.

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Jim Brown-10

Re: KAT500 update

In reply to this post by Jim AB3CV

On 12/8/2011 7:42 PM, Ron D'Eau Claire wrote:
> "sufficient impedance". A normal rule
> of thumb is to have choking impedance 10X the line impedance.

In my tutorial, I've shown that for several important reasons, 5,000
ohms is a far better design goal, that 10K may not be enough for certain
extreme conditions running maximum legal power, and that 500 ohms is
quite inadequate.

73, Jim K9YC
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KEN-3

Re: Balun on tuner input?

In reply to this post by Alan Bloom

On Dec 8, 2011, at 10:51 PM, Alan Bloom wrote:

> The disadvantage of putting the balun at the input is that none of the
> tuner circuitry can be grounded. For example, the control shafts of the
> variable capacitors have RF voltage on them, so the knobs must be
> isolated.

If you have the balun on the input to the tuner, can you have ANY SO-239 outputs and still be balanced? Or it it limited to balanced line output ONLY (e.g. open wire or ladder line), no coax outputs?

Ken
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Geoffrey Mackenzie-Kennedy-3

Re: KAT500 update

In reply to this post by Don Wilhelm-4

May I add to Don's comment by noting that other benefits to be gained from
the use of a properly designed link coupled tuner (we used to call them
Antenna Matching Units or AMUs) are:

1) This type of tuner being a bandpass circuit helps to reduce the level of
unwanted signals reaching the receiver, e.g. Medium and Shortwave broadcast
signals, which if not reduced in level could result in receiver
generated intermodulation products being heard. This type of tuner also
reduces the level of the transmitter's harmonics reaching the antenna.

2) That if a ferrite or iron cored balun (sorry Jim) is used with this type
of tuner, it would be placed in the link circuit where the impedance is 50
+j0 ohms - or close to this value, and it would not be exposed to
large values of reactance.

3) Placing a balun at the end of a feeder exposes the balun to all of the
signals arriving down the feeder, which in some situations could be strong
e.g. Medium Wave and / or Shortwave BC signals. This could result in
numerous intermodulation products being generated by the balun's core, some
of which might end up in our bands. One has to careful
as well that a ferrite/ iron cored balun connected to the feeder or
antenna's feedpoint does not increase the level of radiated transmitter
harmonics.

73,
Geoff
LX2AO

On Dec.09, 2011 at 3:53 AM, Don Wilhelm wrote:

> For those who want a really high efficiency balanced tuner, go to ARRL
> publications back several years to find a link coupled tuner.

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Cortland Richmond-2

Re: KAT500 update

In reply to this post by wayne burdick

You are assuming that the choking impedance is what the transmission
line used for a winding sees; THAT is always whatever impedance the SWR
presents. The 2500 Ohm choking impedance is only seen by current on the
outside of the cable, a good deal less power (thus voltage) than what is
inside. It need only be insulated enough to prevent arcing from output
to adjacent turns.

Cheers!

Cortland
KA5S

On 12/8/201116:43 n09e wrote:

> Imagine choke constructed with RG174 looped through a toroid 10 times. Also
> imagine output resitstance 2500 Ohms and 100W power.
>
> On input, RG174 has a peak voltage of 100V. No problem.
>
> On output, RG174 has a peak voltage of 1000V. It would melt in seconds.
>
> What is wrong here? Assumptions?
>
> Ignacy

Jim Brown-10

Re: Balun on tuner input?

In reply to this post by Alan Bloom

On 12/8/2011 7:51 PM, Alan Bloom wrote:

> There's a simple way to look at this that requires no high-level math or
> complicated analysis.
> _________ _________
> I1 --> | | | | I3 -->
> --------| |--| |-------
> Transmitter | BALUN | | TUNER | Antenna
> --------| |--| |-------
> I2 --> |_________| |_________| I4 -->
>
> The purpose of the balun is to eliminate the common-mode current. The
> CM current is the NET current, that is, I1 + I2 at the input and I3 + I4
> at the output. The balun does not store electrons, so it must be that:
>
> Input common-mode current = output common-mode current.
>
> That is true for both the balun and the tuner. No matter whether the
> balun is on the transmitter or antenna side of the tuner it does an
> equally good (or bad) job of choking the common-mode currents.
>
> The advantage of putting the balun at the input is that the
> differential-mode voltages and currents (the ones you want) are
> well-controlled because of the constant 50-ohm impedance. The DM
> current or voltage at the output can be much higher, depending on the
> load impedance. Of course, the common-mode current and voltage are the
> same at the input and output, but even so the worst-case stress on the
> balun should be less when it is at the input.
>
> The disadvantage of putting the balun at the input is that none of the
> tuner circuitry can be grounded. For example, the control shafts of the
> variable capacitors have RF voltage on them, so the knobs must be
> isolated.

Change the word "balun" to common mode choke, and I'm with you up to here.

> If it is an automatic antenna tuner, that is less of a problem.

Except that the automatic circuitry, and it's power supply must also be
isolated from ground. That part of the design problem seems non-trivial.

> Bottom line? The ARRL is not necessarily "wrong" to put the balun at
> the tuner input. It's just a matter of whether you think the lower
> worst-case current/voltage on the balun is worth the hassle of floating
> the tuner ground.

I agree with your analysis, Alan, with the exception noted.

73, Jim K9YC

>
> Alan N1AL
>
>
> On Thu, 2011-12-08 at 18:59 -0500, Don Wilhelm wrote:
>> This is of interest to me, because in my first experiences with antenna
>> forums (or was it newsgroups at the time), I recall a lot of exchanges
>> with Tom W8JI on exactly the "balun at the tuner input and isolated
>> unbalanced tuner". I concur with Tom - it does not work -- both from a
>> theoretical basis, and also from Tom's measurements.
>>
>> This was "way back when" - as I recall my situation when all this was
>> going on, I was running Windows 95 and the year was between 1997 and 1998.
>>
>> In the timeframe of this discussion, Zack Lau (ARRL engineer) who had
>> first published the "balun at the tuner input" concept as a QRP tuner,
>> had retracted that design because it did not maintain balance, but Dean
>> Straw (ARRL engineer, editor, etc.) published his design of a high power
>> tuner using the same concepts, and that design can still be seen in the
>> ARRL publications.
>>
>> Apologies for the comments into the politics of the ARRL decisions on
>> what is to be published, but that is both a bit of the history as I know
>> it as well as my view of the technical side of this issue.
>>
>> If anyone can tell me how you can run a signal through a balun - and
>> have equal and opposite currents at its output, and then run it through
>> an unbalanced network with unequal elements in the two series legs and
>> still maintain equal and opposite currents and phase, and I will then
>> concede that an isolated unbalanced tuner with a balun at the input will
>> work, but until that is presented to me along with detailed engineering
>> level test data (not just "it works"), I will continue to believe that
>> using a balun on the input of an isolated unbalanced tuner is a "pipe
>> dream" that does not mesh with reality.
>>
>> 73,
>> Don W3FPR
>>
>> aOn 12/8/2011 6:28 PM, Eric Swartz - WA6HHQ, Elecraft wrote:
>>> Hi Ignacy,
>>>
>>> This is a common misconception. (One which I held until recently. :-) It
>>> turns out there is no advantage to placing the balun at the input of the
>>> L-Network tuner. Since one end of the balun is grounded by the input to
>>> the tuner, it is still presented with the same stresses under high SWR
>>> situations. Baluns at the input and output both drive balanced loads
>>> equally well.
>>>
>>> We've now put together a web page describing the impact of placing the
>>> balun at the input or at the output of a L-Network tuner. See:
>>>
>>> http://www.elecraft.com/KAT500/input_versus_output_balun.htm
>>>
>>> At the bottom of that page are several links providing detailed
>>> technical analysis of these configurations. The first two, by W8JI and
>>> W7EL are very clear discussions of this issue.
>>>
>>> 73, Eric WA6HHQ
>>>
>>> www.elecraft.com
>>>
>>>
>>> On 12/8/2011 3:17 PM, Ignacy wrote:
>>>> It seems to me that the story is more complex than it sounds.
>>>>
>>>> The input balun always works at low SWR and at 50 Ohm. It is very easy to
>>>> have such balun. A small balun would easily handle a KW without heating.
>>> ______________________________________________________________
>
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Alan Bloom

Re: Balun on tuner input?

In reply to this post by KEN-3

If the balun is at the input, then there can be only one antenna
connected at the output. I guess that's another reason to put the balun
at the output.

Alan N1AL

On Fri, 2011-12-09 at 05:07 -0500, Ken wrote:

> On Dec 8, 2011, at 10:51 PM, Alan Bloom wrote:
>
> > The disadvantage of putting the balun at the input is that none of the
> > tuner circuitry can be grounded. For example, the control shafts of the
> > variable capacitors have RF voltage on them, so the knobs must be
> > isolated.
>
>
> If you have the balun on the input to the tuner, can you have ANY SO-239 outputs and still be balanced? Or it it limited to balanced line output ONLY (e.g. open wire or ladder line), no coax outputs?
>
> Ken
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Ross Primrose N4RP

Re: Balun on tuner input?

In reply to this post by Jim Brown-10

On 12/9/2011 6:09 PM, Jim Brown wrote:
>
>> If it is an automatic antenna tuner, that is less of a problem.
> Except that the automatic circuitry, and it's power supply must also be
> isolated from ground. That part of the design problem seems non-trivial.
>

Seems fairly simple to me, use a transformer in the PS, and float the
secondary side...

73, Ross N4RP

--
FCC Section 97.313(a) “At all times, an amateur station must use the minimum transmitter power necessary to carry out the desired communications.”

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