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OT Tuner Basics

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Jeff Wandling W7BRS-2

OT Tuner Basics

Elecrafters,

I know this is off-topic, but the range of ham-smarts on this list is
pretty good so I'll throw the question here and hopefully get some of that
ham-smarts too.

OK -- K3/100 with KAT3 is the rig.

I have it connected through a tuner and then to the SB-200 and then Dipole

K3/100/ATU <-> MFJ tuner <-> SB200 <-> Dipole

If I use Auto mode on the KAT3, put the MFJ tuner in Bypass and hold TUNE
then the KAT3 goes and brings the SWR (according to the display) to a
favorable value (1.0 to 1.2). I use a MFJ tuner between my Rig and Amp
because the Old Bard told me to. Actually my setup is different than
what I just described, but I'm simplifying this for the question at hand.

[ What I really do is K3 <-> Small MFJ Tuner <-> SB200 <-> Big MFJ Tuner
<-> Dipole ]

On the watt meter of the (small) MFJ Tuner, the indication is I have a non
favorable SWR, more reflected power than had I put the KAT3 in bypass and
manually tuned the MFJ Tuner to a favorable SWR (1.0 to 1.2 or so).

So, can someone explain in basic terms what's happening when I use Auto
mode on the KAT3 and see favorable SWR on the KAT3 (via K3 display) but do
not see favorable SWR on the MFJ tuner?

This is not a round-about way of expressing a problem with the K3. On the
contrary - I couldn't be more pleased with the KAT3 performance and so
forth.

I'm asking this question as a data-point before I decide to build the KAT2
for my finished K2.

Thanks in advance,

-jeff

--
Jeff Wandling DE W7BRS K3 #2105 http://w7brs.com/k3
[hidden email]
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Jeff Wandling W7BRS-2

Re: OT Tuner Basics (correction)

Correction:

The button I push to invoke the Auto tuner on the K3, is ATU TUNE, not
TUNE. I mis-typed. I meant ATU TUNE.

Also, there is only one ATU in the scenario -- the KAT3. The MFJ tuners
are not ATUs.

Thanks.

-jeff

--
Jeff Wandling DE W7BRS K3 #2105 http://w7brs.com/k3
[hidden email]

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John W2XS

Re: OT Tuner Basics

In reply to this post by Jeff Wandling W7BRS-2

"So, can someone explain in basic terms what's happening when I use Auto
mode on the KAT3 and see favorable SWR on the KAT3 (via K3 display) but do
not see favorable SWR on the MFJ tuner?"

In order for an SWR meter to read the matched condition properly, it must be between the tuner and the rig. Your small MFJ is between the tuner (KAT3) and the antenna (or amplifier), so it is on the "wrong" side of the tuner.

I use the KAT3 and an external balun. Even though there is a short run of coax connecting the K3 and the balun, I cannot use my external power/SWR meter there when using the built-in tuner because it is "outside" the part of the circuit that is being matched by the tuner.

I once thought about adding another coax connecter to get the external power meter in between the rig and the KAT3 tuner, but now I am used to the K3's SWR and power meters and am fine with it.

73,

John W2XS

Don Wilhelm-4

Re: OT Tuner Basics

In reply to this post by Jeff Wandling W7BRS-2

Jeff,

Any antenna tuner, including the MFJ, the KAT3, or any other does not
actually "tune" the antenna. It adds a network of inductance and
capacitance between its input and output to allow the input impedance to
be near 50 ohms resistive while the output impedance will be whatever it
was to start with.

What I am trying to say is that an SWR meter placed at the output of the
KAT3 will not change before, during, or after tuning the KAT3 (unless
there is something wrong in the antenna system) - nothing is changed on
the output side of the tuner. The only thing that will change is the
impedance looking into the tuner input, and that is the SWR indicated by
the K3 using its internal wattmeter. The KAT3 arranges its internal
inductance and capacitance so it is a transmission line transformer of
the proper ratio to produce a 50 ohm match to the K3 PA to operate into.

Take the small MFJ tuner between your SB200 and the K3 away, it serves
no purpose that I can think of.

With the SB-200 and the high power tuner both set to bypass, the KAT3
should be able to match the antenna. When you put the SB-200 in-line,
you should set the KAT3 to bypass, and if the amp input circuit does not
offer a low enough SWR to properly operate the K3, then whatever problem
that exists should be fixed in the amplifier. The large MFJ will have
to be tuned manually to match the output of the SB-200 to your antenna -
the same as the KAT3 did for you automatically when the SB-200 and large
MFJ tuner were bypassed.

BTW, the easiest way to adjust a manual tuner is to connect an antenna
analyzer to the tuner input and then tune until you have a low SWR or
ideally a R=50, X=0 impedance indication. After that, connect the tuner
to the SB-200 and operate (on that band or band portion) without
touching the tuner settings any further.
As long as your antenna does not change, you can record the tuner
settings for quickly resetting the tuner when operating on that
frequency the next time.

73,
Don W3FPR

W7BRS wrote:

> Elecrafters,
>
> I know this is off-topic, but the range of ham-smarts on this list is
> pretty good so I'll throw the question here and hopefully get some of that
> ham-smarts too.
>
> OK -- K3/100 with KAT3 is the rig.
>
> I have it connected through a tuner and then to the SB-200 and then Dipole
>
> K3/100/ATU <-> MFJ tuner <-> SB200 <-> Dipole
>
> If I use Auto mode on the KAT3, put the MFJ tuner in Bypass and hold TUNE
> then the KAT3 goes and brings the SWR (according to the display) to a
> favorable value (1.0 to 1.2). I use a MFJ tuner between my Rig and Amp
> because the Old Bard told me to. Actually my setup is different than
> what I just described, but I'm simplifying this for the question at hand.
>
> [ What I really do is K3 <-> Small MFJ Tuner <-> SB200 <-> Big MFJ Tuner
> <-> Dipole ]
>
> On the watt meter of the (small) MFJ Tuner, the indication is I have a non
> favorable SWR, more reflected power than had I put the KAT3 in bypass and
> manually tuned the MFJ Tuner to a favorable SWR (1.0 to 1.2 or so).
>
> So, can someone explain in basic terms what's happening when I use Auto
> mode on the KAT3 and see favorable SWR on the KAT3 (via K3 display) but do
> not see favorable SWR on the MFJ tuner?
>
> This is not a round-about way of expressing a problem with the K3. On the
> contrary - I couldn't be more pleased with the KAT3 performance and so
> forth.
>
> I'm asking this question as a data-point before I decide to build the KAT2
> for my finished K2.
>
> Thanks in advance,
>
> -jeff
>
>

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N5GE

Re: OT Tuner Basics

In reply to this post by Jeff Wandling W7BRS-2

On Thu, 15 Jan 2009 09:15:36 -0800 (PST), you wrote:

[snip]

Comments in line...

>I have it connected through a tuner and then to the SB-200 and then Dipole
>
>K3/100/ATU <-> MFJ tuner <-> SB200 <-> Dipole
>
>If I use Auto mode on the KAT3, put the MFJ tuner in Bypass and hold TUNE
>then the KAT3 goes and brings the SWR (according to the display) to a
>favorable value (1.0 to 1.2). I use a MFJ tuner between my Rig and Amp
>because the Old Bard told me to. Actually my setup is different than
>what I just described, but I'm simplifying this for the question at hand.
>
>[ What I really do is K3 <-> Small MFJ Tuner <-> SB200 <-> Big MFJ Tuner
><-> Dipole ]

I don't know why the "Old Bard" told you to do that. It makes no
sense to me. First of all take the small MFJ tuner out of the line
and connect the K3 directly to the SB200. The tuner in the K3 will do
the job of the small MFJ tuner. No sense adding tuner loss between
the Amp and the rig. I suspect the "Old Bard" told you that because
the input of the SB200 is not 50 ohms. More about that later...

>On the watt meter of the (small) MFJ Tuner, the indication is I have a non
>favorable SWR, more reflected power than had I put the KAT3 in bypass and
>manually tuned the MFJ Tuner to a favorable SWR (1.0 to 1.2 or so).

This indicates that the SB200 input is not 50 ohms. You may have some
troubles with the SB200 input, but you should be able to adjust that.
Look at the SB200 manual and see if it has input matching adjustments.

You certainly don't need two tuners for the SB200 input!

>
>So, can someone explain in basic terms what's happening when I use Auto
>mode on the KAT3 and see favorable SWR on the KAT3 (via K3 display) but do
>not see favorable SWR on the MFJ tuner?

Here's what is going on. In the configuration you have now, you are
correcting the mismatch between the small tuner and the K3. When you
remove the small tuner you will be seeing the input of the large tuner
(If you have the amp turned off or in standby.)

When you use a tuner on an antenna, you don't change the antenna, you
change what the rig sees at the feed end of the coax.

I have an amplifier and large tuner. Here is what I do when using an
antenna that doesn't have a good match.

1. Put the K3 in tune (hold the XMIT button). Adjust the large tuner
connected to the output of the Amplifier for the lowest SWR. You want
the amp turned off or in standby at this point.

2. Turn off the tune on the K3.

3. Make sure the power setting on the K3 is set below the normal
drive power of the Amp.

4. Turn the amp on or take it out of standby. Hold the XMIT button in
on the K3 and adjust the amplifier's tune and load according to the
manual that came with it. Your K3 tune level should be about 15 or 20
watts or something below the full output drive of the amp. Turn off
the K3 tune.

5. If, and only if you saw a high SWR on the K3 meter, tap the ATU
Tune button and tune the K3 to the input of the amp.

6. Hold your CW key or what ever your using to send input power to
the amp and adjust the amp tune and load for the output you want from
it.

Now you're good to go :o)

73,

Tom, N5GE
http://www.n5ge.com
http://www.swotrc.net

[snip]

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Amateur Radio Operator N5GE

KH7T

Re: OT Tuner Basics

In reply to this post by Jeff Wandling W7BRS-2

Many of the questions about use of extra tuners with an ATU are answered
by a review of the fundamental assumptions for the design of simple
(cheap) power and swr meters.

Most common tuners assume that the input to the tuner is 50 ohms. The
SWR calibration is based on the ratio of reflected to forward power. If
the input impedance is not 50 ohms then calculation of power is not
accurate because the meters are not smart enough to measure actual power
based on the true input impedance. They indicate power based on a
voltage or current measurement. The real power will vary if the input
impedance changes.

When two tuners are used in series, such as the K3 ATU to an MFJ* to an
amplifier, the impedance at the output of the ATU and the input to the
MFJ is rarely 50 ohms. Only if the amplifier input is 50 ohms resistive
and the MFJ is bypassed, then the SWR indicated by the MFJ might be
close to 1 to 1 after the ATU is tuned.

However, if the amplifier input impedance is perhaps 100 ohms, then the
ATU will match the 100 ohms and the MFJ measurements will be referenced
to the 100 ohms. The SWR based on forward and reflected power indicated
by the MFJ will not be accurate. The forward power indicated by the MFJ
may show twice the real input power when the input termination is 100
ohms. Power = (V squared)/R. As you can see the indicated power
changes as the resistance changes. The real power is not changed, just
the reference has changed and is not accounted for.

So, do not waste time reading the power at the output of an ATU unless
you know that the load is 50 ohms. Bypass the ATU and use the MFJ and
you may get a reasonable indication on the MFJ when the transmitter
output impedance is 50 ohms. Or delete the MFJ and use the ATU
indicators.

Now if you have a true power measuring watt meter that actually
calculates current times voltage without using the input impedance as a
reference then these measurements might be of some interest.

* MFJ is used here to represent the most commonly available SWR meters
using forward and reverse power indicators that assume a 50 ohm input
impedance including the common Bird and others.

I did not get into the additional errors introduced when the reference
is a complex impedance and not just a simple resistance. True power is
based only of the resistive part of the impedance. So again the error
is compounded with the simple P=(I squared) times R approach

Aloha,
John KH7T

W7BRS wrote:

Jeff Wandling W7BRS-2

Re: OT Tuner Basics

In reply to this post by N5GE

I may have led this question astray.. I hope this wraps it.

> Comments in line...
>> I have it connected through a tuner and then to the SB-200 and then Dipole
>>
>> K3/100/ATU <-> MFJ tuner <-> SB200 <-> Dipole
>>
>> If I use Auto mode on the KAT3, put the MFJ tuner in Bypass and hold TUNE
>> then the KAT3 goes and brings the SWR (according to the display) to a
>> favorable value (1.0 to 1.2). I use a MFJ tuner between my Rig and Amp
>> because the Old Bard told me to. Actually my setup is different than
>> what I just described, but I'm simplifying this for the question at hand.
>>
>> [ What I really do is K3 <-> Small MFJ Tuner <-> SB200 <-> Big MFJ Tuner
>> <-> Dipole ]
>
> I don't know why the "Old Bard" told you to do that. It makes no
> sense to me. First of all take the small MFJ tuner out of the line
> and connect the K3 directly to the SB200. The tuner in the K3 will do
> the job of the small MFJ tuner. No sense adding tuner loss between
> the Amp and the rig. I suspect the "Old Bard" told you that because
> the input of the SB200 is not 50 ohms. More about that later...

I thought I wrote it, but perhaps it was ommited.

When I run the K3/100/ATU I put the small tuner between the Rig and the
amp in Bypass. It's more or less an RF speed bump when I use the K3 ATU.

I do not tune with the rig-to-amp tuner ever, when I use the K3. I merely
was indicating that I glance at the power meter on it and was wondering
about that when I was using the K3/ATU in AUTO.

The K3 is not my only rig. When I select a different transmitter,
one that does not have an ATU, then I do need the small tuner between the
other rig and the amp. Hence, that is why it's inline. The old-bard
remark was in context of using a NON-ATU-equipped rig before the amp.

> This indicates that the SB200 input is not 50 ohms. You may have some
> troubles with the SB200 input, but you should be able to adjust that.
> Look at the SB200 manual and see if it has input matching adjustments.
>
> You certainly don't need two tuners for the SB200 input!

I certainly agree. I leave the conventional tuner between the rig and
SB-200 in bypass when I use the K3. My K2 has no ATU so I need it then.
My K3 has an ATU so I don't need it then.

>> So, can someone explain in basic terms what's happening when I use Auto
>> mode on the KAT3 and see favorable SWR on the KAT3 (via K3 display) but do
>> not see favorable SWR on the MFJ tuner?
>
> Here's what is going on. In the configuration you have now, you are
> correcting the mismatch between the small tuner and the K3. When you
> remove the small tuner you will be seeing the input of the large tuner
> (If you have the amp turned off or in standby.)

That is precisely what I was doing before I owned the K3/100/ATU. I would
match the rig (YaeKenCom) radio without an ATU.

See above about putting it into bypass when I'm operating K3/100/ATU.

> 1. Put the K3 in tune (hold the XMIT button). Adjust the large tuner
> connected to the output of the Amplifier for the lowest SWR. You want
> the amp turned off or in standby at this point.

[steps]

Yes, I do that too. In my station, I put the analyzer so that I can
select a transmitter of K3, YaeKenCom, or Analyzer. This way the coax
path is nearly identical between the analyzer down to ant. vs. the rig
down to ant. Not identical but close enough that when the time comes to
put the key down my match is pretty close and I trim it up on the big
tuner (amp to antenna).

Then when I select analyzer, I read the R/Z/SWR values off the analyzer as
I do my darndest to match with the manual conventional tuner between the amp
and antenna (big MFJ tuner).

Then when I got it setup, I switch Tx back to K3, and use the AUTO tune
function of the K3's ATu to polish up and away I go with nearly full PEP
power that I can get.

In all instances that I use the K3/ATU, the tuner between the K3 and Amp
is in bypass. In all instances that I do not use the K3/ATU then the
tuner between the other rig and the amp is NOT in bypass.

In all instances the big-tuner between the Amp and Antenna is NOT in
bypass.

> Now you're good to go :o)

I think so, thanks!

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Jan Erik Holm

Re: OT Tuner Basics

In reply to this post by N5GE

> Tom, N5GE wrote:
>
> This indicates that the SB200 input is not 50 ohms. You may have some
> troubles with the SB200 input, but you should be able to adjust that.
> Look at the SB200 manual and see if it has input matching adjustments.

Yes it has. Take amp out from the green cover, tune the input coils from
behind, it´s easy.

73 Jim SM2EKM

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Jeff Wandling W7BRS-2

Re: Summary OT Tuner Basics

In reply to this post by Jeff Wandling W7BRS-2

Gotta hand it to Tom, N0SS, for putting it in clearer symbols.

Anyway, he made this: http://w7brs.com/n0ss+ant.pdf

That's what I got going on. And, after all the email it seems clear
what's happening. Thanks all.

-jeff

--
Jeff Wandling DE W7BRS K3 #2105 http://w7brs.com/k3
[hidden email]

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N5GE

Re: OT Tuner Basics

In reply to this post by Jeff Wandling W7BRS-2

On Thu, 15 Jan 2009 11:20:37 -0800 (PST), you wrote:

>
>I may have led this question astray.. I hope this wraps it.
[snip]

>
>Yes, I do that too. In my station, I put the analyzer so that I can
>select a transmitter of K3, YaeKenCom, or Analyzer. This way the coax
>path is nearly identical between the analyzer down to ant. vs. the rig
>down to ant. Not identical but close enough that when the time comes to
>put the key down my match is pretty close and I trim it up on the big
>tuner (amp to antenna).
>
>Then when I select analyzer, I read the R/Z/SWR values off the analyzer as
>I do my darndest to match with the manual conventional tuner between the amp
>and antenna (big MFJ tuner).
>
>Then when I got it setup, I switch Tx back to K3, and use the AUTO tune
>function of the K3's ATu to polish up and away I go with nearly full PEP
>power that I can get.
>
>In all instances that I use the K3/ATU, the tuner between the K3 and Amp
>is in bypass. In all instances that I do not use the K3/ATU then the
>tuner between the other rig and the amp is NOT in bypass.
>
>In all instances the big-tuner between the Amp and Antenna is NOT in
>bypass.
>
>> Now you're good to go :o)
>
>I think so, thanks!

Great!

If you tune the input coils in the amp as Jan suggests you may even be
able to bypass the K3 tuner also.

Tom, N5GE
http://www.n5ge.com
http://www.swotrc.net

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Amateur Radio Operator N5GE

john lawrence-3

Re: OT Tuner Basics

In reply to this post by Jeff Wandling W7BRS-2

John,

Your K3 auto tune option within the K3 and the SB200 should take care of any amplifier input mismatches found on the turned circuits within the grounded grid amplifier. In more technical terms, the impedance range of the KAT3 should be adequate. Having a second tuner in between the K3 and the amplifier doesn't help. In fact, there are a number of reasons it will make the combination not work to it's fullest efficiency. ie network losses. The reason why you are seeing varying VSWR readings is most likely due to changes in coax line length between the K3 and amplifier, with and without the additional tuner. Reading the K3 manual it says the internal auto tuner can handle a fairly wide VSWR range. If you find that some of the bands are problematic due to the internal tuner not able to tune out the VSWR into the amp, then I'd attempt tuning the powdered iron core (one per band) on the amp's input circuit.

I am a new user on the learning curve with my K3 S/N 2270 and this is my first post. It's an exciting way to stay young. If you'd like to make a schedule on 80 meter ssb to talk about K3 details I'd be delighted. In fact, I'd like to establish a Northeast OT'ers User's Group to meet on 80 meter schedules. What do you or anyone else who is interested in meeting on 80 meters within day time, (8AM) mid week availability think about this idea? Pre retired baby boomers and their children would be welcome too.

73,

John, W1QS ex N6JL, K1KTH and KA7AB

John Lawrence
Pond Brook Farm
North Waldoboro, Maine 04572
207-615-2824