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K3 (not S) Antenna tuner strangeness

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briancom

K3 (not S) Antenna tuner strangeness

Guys,

I've run into something on 80M trying to use the internal antenna tuner.
It fails to tune to a low SWR.

My recollection is that the tuner worked fine on the same antenna
before. "Worked before" may have been with a slightly different tap
position.

Antenna is an MFJ 1/8 Wave vertical with loading coil and 4:1 "Guanella"
balun at the antenna base.

With the current coil tap an RF analyst antenna analyzer shows the
following:

3.55 MHz SWR=2.0 Z=35 ohms
3.6 SWR=2.7 Z=36 ohms

The K3 in the tune position (tuner out) shows SWR's of 1.7 and 2.4
respectively.

The antenna tuner finds a match for a 50 ohm dummy load OK. Using those
settings as a starting point, we attempted to match the antenna.

The best it can do is bring the 1.7 SWR down to 1.4. The 2.0 SWR can
brought down to 1.7 at best.

Other bands work OK.

Any thoughts?

73 de Brian/K3KO
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Nr4c

Re: K3 (not S) Antenna tuner strangeness

Try a “slightly different tap position” and see what happens. Your words, not mine.

…bill nr4c

> On Jul 22, 2016, at 12:19 PM, brian <[hidden email]> wrote:
>
> Guys,
>
> I've run into something on 80M trying to use the internal antenna tuner.
> It fails to tune to a low SWR.
>
> My recollection is that the tuner worked fine on the same antenna before. "Worked before" may have been with a slightly different tap position.
>
> Antenna is an MFJ 1/8 Wave vertical with loading coil and 4:1 "Guanella" balun at the antenna base.
>
> With the current coil tap an RF analyst antenna analyzer shows the following:
>
> 3.55 MHz SWR=2.0 Z=35 ohms
> 3.6 SWR=2.7 Z=36 ohms
>
> The K3 in the tune position (tuner out) shows SWR's of 1.7 and 2.4 respectively.
>
> The antenna tuner finds a match for a 50 ohm dummy load OK. Using those settings as a starting point, we attempted to match the antenna.
>
> The best it can do is bring the 1.7 SWR down to 1.4. The 2.0 SWR can brought down to 1.7 at best.
>
> Other bands work OK.
>
> Any thoughts?
>
> 73 de Brian/K3KO
> ______________________________________________________________
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John G3PQA

Re: K3 (not S) Antenna tuner strangeness

In reply to this post by briancom

Guys,
I've run into something on 80M trying to use the internal antenna tuner.
It fails to tune to a low SWR. Brian K3KOI had a similar problem but never quite got to the bottom of it because partly intermittent, possibly multiple faults.
In the end to fix it:-
a) I rewound one of the swr sensor toroids (centre wire had possibly arced to ferrite because I disconnected antenna by mistake and tuned), and
b) fixed a new earthing wire between KAT3 chassis and SO259 Ant1 socket body. (possible poor earth connection via KAT3 securing pillar to side panel)
John G3PQA
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Don Wilhelm

Re: K3 (not S) Antenna tuner strangeness

John,

Yes, the "earthing" connection to the SO-239 jacks is important.
That connection is provided by the mechanical connection to the standoff
between the right side panel and the KAT3.
The assembly manual instructions will provide adequate connection -
first insert the side panel screw through the 2-D connector and then
tighten the standoff to the 2D connector, and lastly, put the screw and
lockwasher into the standoff.

The problem is that *if* that long screw in the upper rear corner of the
right side panel is removed for any reason, it cannot be tightened
properly without going through the entire procedure - tighten the 2D
connector, then tighten the standoff and finally tighten the screw into
the standoff.

If one tries to remove that screw from the right side panel, it is
impossible to re-tighten everything without going through the entire
process in order. The threads of the 2D connector cannot be properly
tightened to the threads of the standoff.

A shortcut is to drill out the screw threads on that 2D connector
allowing the screw to pass through the 2D connector without threads.
That will permit the screw threads to pass through the 2D connector and
be tightened onto the standoff.

I recommend that anyone removing the right side panel from their K3/K3S
to drill out the threads in this hole of the 2D connector so it can be
assembled tightly without going through the entire procedure of first
tightening the 2D connector, then the standoff and finally the screw and
lockwasher.

73,
Don W3FPR

On 7/23/2016 9:09 PM, [hidden email] wrote:
> Guys,
> I've run into something on 80M trying to use the internal antenna tuner.
> It fails to tune to a low SWR. Brian K3KOI had a similar problem but never quite got to the bottom of it because partly intermittent, possibly multiple faults.
> In the end to fix it:-
> a) I rewound one of the swr sensor toroids (centre wire had possibly arced to ferrite because I disconnected antenna by mistake and tuned), and
> b) fixed a new earthing wire between KAT3 chassis and SO259 Ant1 socket body. (possible poor earth connection via KAT3 securing pillar to side panel)
> John G3PQA
>

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briancom

Re: K3 (not S) Antenna tuner strangeness

Hi Don,

Further insight needed.

John and I have looked into the 80M tuner strangeness problem further.
We both have qualitatively seen the same thing. It is related to trying
to tune Z's that are on the order of 25-30 ohms on 160M/80M.

John already addressed the grounding issue in his K3.

The original problem raised was trying to tune a vertical antenna on 80M
which had a measured R=30 ohms and XL =18 ohms. The tuner only slightly
reduced the SWR. Repeated presses of ATU Tune did not improve things.

A calculation of the L network component values needed to match this
load shows L/C values well within the range that the KAT could switch in.

I then tried matching a 25 ohm pure resistive load-- two 50 ohm dummy
loads in parallel. One would think this kind of load could easily be
matched. Not so. It would match only on the upper end of 80M and not at
all on 160M. The tuner did not reduce the 2:1 SWR at all on 160M and
only brought it down a few tenths on the low end of 80.

It is interesting to note that the high end of 80 match used L/C values
greater than needed in the vertical antenna to match it.

John tried other resistive and combined resistive/reactive loads. Here
are his results.

Freq Load value measured SWR on K3 SWR on K3 after KAT3 tune
1.836 23.5 (via 1 m. RG213) 1.6 1.6
1.836 32+j28 2.5 1.0
3.522 23.5 1.6 1.3
3.522 56+j55 3.0 1.0
7.006 23.5 1.5 1.0
7.006 132-j76 4.0 1.0
10.100 23.5 1.3 1.0
10.100 30-j48 4.0 1.0

So we have two different K3's having the same qualitative matching
problem with lower Z loads on 80/160.

Of course it is possible that both KAT tuners have other component failures.

It would be interesting if others would try the two paralleled dummy
load experiment.

Elecraft suggested shorting out the 8.215 MHz trap in series with the
ATU/output. They say the trap has been removed in later KAT versions.
The trap consists of parallel 96 nH and 3900 pf components.

It is not clear that would fix this particular issue. It undoubtedly
was a fix for other issues.

Looking at the component values and parallel configuration:
1) Both shorted would be the Elecraft fix
2) Open C: Parallel inductor would shunt the RF around the failed cap.
On 80/160 the added series reactance would be <2 ohms.
3) Open inductor: Parallel C would introduce a series reactance of less
than an ohm.
4) Both open, the tuner would not match on any band.

So we are left with a mystery.

Why are lower Z (~25-30 ohm) loads so hard to match on 80/160?

It would be instructive if others have luck matching the 25 ohm
paralleled dummy load case on 80/160.

Insight in where else to look would be welcomed.

73 de Brian/K3KO

On 7/25/2016 2:35 AM, Don Wilhelm wrote:

> John,
>
> Yes, the "earthing" connection to the SO-239 jacks is important.
> That connection is provided by the mechanical connection to the standoff
> between the right side panel and the KAT3.
> The assembly manual instructions will provide adequate connection -
> first insert the side panel screw through the 2-D connector and then
> tighten the standoff to the 2D connector, and lastly, put the screw and
> lockwasher into the standoff.
>
> The problem is that *if* that long screw in the upper rear corner of the
> right side panel is removed for any reason, it cannot be tightened
> properly without going through the entire procedure - tighten the 2D
> connector, then tighten the standoff and finally tighten the screw into
> the standoff.
>
> If one tries to remove that screw from the right side panel, it is
> impossible to re-tighten everything without going through the entire
> process in order. The threads of the 2D connector cannot be properly
> tightened to the threads of the standoff.
>
> A shortcut is to drill out the screw threads on that 2D connector
> allowing the screw to pass through the 2D connector without threads.
> That will permit the screw threads to pass through the 2D connector and
> be tightened onto the standoff.
>
> I recommend that anyone removing the right side panel from their K3/K3S
> to drill out the threads in this hole of the 2D connector so it can be
> assembled tightly without going through the entire procedure of first
> tightening the 2D connector, then the standoff and finally the screw and
> lockwasher.
>
> 73,
> Don W3FPR
>
> On 7/23/2016 9:09 PM, [hidden email] wrote:
>> Guys,
>> I've run into something on 80M trying to use the internal antenna tuner.
>> It fails to tune to a low SWR. Brian K3KOI had a similar problem but
>> never quite got to the bottom of it because partly intermittent,
>> possibly multiple faults.
>> In the end to fix it:-
>> a) I rewound one of the swr sensor toroids (centre wire had possibly
>> arced to ferrite because I disconnected antenna by mistake and tuned),
>> and
>> b) fixed a new earthing wire between KAT3 chassis and SO259 Ant1
>> socket body. (possible poor earth connection via KAT3 securing pillar
>> to side panel)
>> John G3PQA
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Wes Stewart-2

Re: K3 (not S) Antenna tuner strangeness

There is something wrong with the unmatched SWR values you measured/posted.

If your load is actually 23.5 +j0 then the beginning SWR is ~2.1:1, not the 1.6
you list. That's not to say that the tuner shouldn't do something with it but
it does point to something amiss. Likewise the values you give for 4:1 are
closer to 3.6:1

On 7/25/2016 6:30 AM, brian wrote:

> Hi Don,
>
> Further insight needed.
>
> John and I have looked into the 80M tuner strangeness problem further.
> We both have qualitatively seen the same thing. It is related to trying to
> tune Z's that are on the order of 25-30 ohms on 160M/80M.
>
> John already addressed the grounding issue in his K3.
>
> The original problem raised was trying to tune a vertical antenna on 80M which
> had a measured R=30 ohms and XL =18 ohms. The tuner only slightly reduced the
> SWR. Repeated presses of ATU Tune did not improve things.
>
> A calculation of the L network component values needed to match this load
> shows L/C values well within the range that the KAT could switch in.
>
> I then tried matching a 25 ohm pure resistive load-- two 50 ohm dummy loads in
> parallel. One would think this kind of load could easily be matched. Not so.
> It would match only on the upper end of 80M and not at all on 160M. The tuner
> did not reduce the 2:1 SWR at all on 160M and only brought it down a few
> tenths on the low end of 80.
>
> It is interesting to note that the high end of 80 match used L/C values
> greater than needed in the vertical antenna to match it.
>
> John tried other resistive and combined resistive/reactive loads. Here are his
> results.
>
> Freq Load value measured SWR on K3 SWR on K3 after KAT3 tune
> 1.836 23.5 (via 1 m. RG213) 1.6 1.6
> 1.836 32+j28 2.5 1.0
> 3.522 23.5 1.6 1.3
> 3.522 56+j55 3.0 1.0
> 7.006 23.5 1.5 1.0
> 7.006 132-j76 4.0 1.0
> 10.100 23.5 1.3 1.0
> 10.100 30-j48 4.0 1.0
>
> So we have two different K3's having the same qualitative matching problem
> with lower Z loads on 80/160.
>
> Of course it is possible that both KAT tuners have other component failures.
>
> It would be interesting if others would try the two paralleled dummy load
> experiment.
>
> Elecraft suggested shorting out the 8.215 MHz trap in series with the
> ATU/output. They say the trap has been removed in later KAT versions.
> The trap consists of parallel 96 nH and 3900 pf components.
>
> It is not clear that would fix this particular issue. It undoubtedly was a
> fix for other issues.
>
> Looking at the component values and parallel configuration:
> 1) Both shorted would be the Elecraft fix
> 2) Open C: Parallel inductor would shunt the RF around the failed cap. On
> 80/160 the added series reactance would be <2 ohms.
> 3) Open inductor: Parallel C would introduce a series reactance of less than
> an ohm.
> 4) Both open, the tuner would not match on any band.
>
> So we are left with a mystery.
>
> Why are lower Z (~25-30 ohm) loads so hard to match on 80/160?
>
> It would be instructive if others have luck matching the 25 ohm paralleled
> dummy load case on 80/160.
>
> Insight in where else to look would be welcomed.
>
> 73 de Brian/K3KO

Brian Hunt

Re: K3 (not S) Antenna tuner strangeness

In reply to this post by briancom

Hi Brian,
Just a thought, but given the KAT3 uses discrete components for C and L,
what you are seeing may be as close as you can get. If you have
calculated the tuner parameters from the Z you are seeing at the antenna
going into the tuner, compare those with the discrete combinations
possible in the tuner. Find the closest ones and then work backwards to
the SWR value. SimSmith Smith chart software is great for this. The
KAT3 schematic is included in the K3 schematics .pdf file.

I ran into a similar situation on 40 meters with an MFJ remote
autotuner. Drove me nuts until I figured it out.

Good luck!

Brian, K0DTJ

On 7/25/2016 06:30, brian wrote:
> Further insight needed.
>

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Don Wilhelm

Re: K3 (not S) Antenna tuner strangeness

In reply to this post by briancom

Brian,

You might try going into the KAT3 menu and go through the L1-L8 and
C1-C8 settings to hear the relays click with each selection.

If all the relays are working, you should be able to do a check on the
health of the inductors and capacitors using a method similar to that
shown for the KAT100 in the right column of page 35 - manually select
the inductors starting with L1 and see what the SWR is on a high band.
With each other inductor, the SWR should increase. Change to a lower
band if the SWR gets too high to indicate (highest is 9.9). Do the same
for the capacitors.

I have not tried this technique with the KAT3 (but it should work) - I
have used it with the KAT100 and the KAT2.

73,
Don W3FPR

On 7/25/2016 9:30 AM, brian wrote:
> Hi Don,
>
> Further insight needed.
>
> John and I have looked into the 80M tuner strangeness problem further.
> We both have qualitatively seen the same thing. It is related to
> trying to tune Z's that are on the order of 25-30 ohms on 160M/80M.
>

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briancom

Re: K3 (not S) Antenna tuner strangeness

Thanks Don,
Very instructive.
All relays click.
Tabulated below are the L/C test results.
The only anomaly appears to be with C2. It seems to act as a 100 pf
rather than the 22 pf it is supposed to be.

SWR's 50 ohm dummy load attached to antenna port of K3
-------------------------------------
L test
Bypass 1.0 50.1 MHz
L1 1.1
L2 1.8
Bypass 1.0 28.1 MHz
L1 1.0
L2 1.0
L3 1.5
L4 3.3
L5 14
Bypass 1.0 14.10 MHz
L5 3.9
L6 9.8
Bypass 1.0 7.05 MHz
L6 4.2
L7 8.9
Bypass 1.81 MHz
L7 2.3
L8 4.6
-------------------------------------------------
28.1 MHz Bypass = 1.0 21.0 MHz Bypass =1.0
C1 1.4 C1 1.3
C2 2.5 C2 2.1
C3 1.5 C3 1.4
C4 1.7 C4 1.5
C5 5.5
14.1 MHz Bypass =1.0
C5 2.6
C6 5.2
7.05 MHz Bypass =1.0
C6=1.7
C7=3.9
C8=10.9
----------------------------------------------------------
Not sure if the C2 anomaly is relevant to 160/80 M

73 de Brian/K3KO

On 7/25/2016 18:11 PM, Don Wilhelm wrote:

> Brian,
>
> You might try going into the KAT3 menu and go through the L1-L8 and
> C1-C8 settings to hear the relays click with each selection.
>
> If all the relays are working, you should be able to do a check on the
> health of the inductors and capacitors using a method similar to that
> shown for the KAT100 in the right column of page 35 - manually select
> the inductors starting with L1 and see what the SWR is on a high band.
> With each other inductor, the SWR should increase. Change to a lower
> band if the SWR gets too high to indicate (highest is 9.9). Do the same
> for the capacitors.
>
> I have not tried this technique with the KAT3 (but it should work) - I
> have used it with the KAT100 and the KAT2.
>
> 73,
> Don W3FPR
>
> On 7/25/2016 9:30 AM, brian wrote:
>> Hi Don,
>>
>> Further insight needed.
>>
>> John and I have looked into the 80M tuner strangeness problem further.
>> We both have qualitatively seen the same thing. It is related to
>> trying to tune Z's that are on the order of 25-30 ohms on 160M/80M.
>>
>

Don Wilhelm

Re: K3 (not S) Antenna tuner strangeness

Brian,

There should have been an increase in SWR between L1 and L2 on 28MHz,
but the results on 50MHz indicate that it may be OK.

I think the increase in SWR between C1 and C2 is normal, but why does
the SWR drop when C3 is selected? That to me indicates a problem with
C3 - and possibly C4 for the same reason.

The problem can either be the capacitor or its associated relay. The
relays clicking indicate that the coil is OK, but that says little about
the contacts.

Take another look at the C1 through C5 sequence on 28MHz. The SWR
should increase with each successive capacitor selected - simply because
the capacitor values are larger.
From my experience with the KAT2 and KAT100, the SWR increase between
C1 and C2 is normal, but the real question is "Why does it drop
significantly with C3 and C4?"
The C5 SWR of 5.5 is more along the lines of what I would expect.

So I would suspect C3 and C4 -- or more likely their relays above all else.

Yes, those could be the reason you cannot achieve a good match to low
impedance loads on 80 and 160 - it just may be that those values are
needed and are not available.

73,
Don W3FPR

On 7/25/2016 5:23 PM, brian wrote:

> Thanks Don,
> Very instructive.
> All relays click.
> Tabulated below are the L/C test results.
> The only anomaly appears to be with C2. It seems to act as a 100 pf
> rather than the 22 pf it is supposed to be.
>
> SWR's 50 ohm dummy load attached to antenna port of K3
> -------------------------------------
> L test
> Bypass 1.0 50.1 MHz
> L1 1.1
> L2 1.8
> Bypass 1.0 28.1 MHz
> L1 1.0
> L2 1.0
> L3 1.5
> L4 3.3
> L5 14
> Bypass 1.0 14.10 MHz
> L5 3.9
> L6 9.8
> Bypass 1.0 7.05 MHz
> L6 4.2
> L7 8.9
> Bypass 1.81 MHz
> L7 2.3
> L8 4.6
> -------------------------------------------------
> 28.1 MHz Bypass = 1.0 21.0 MHz Bypass =1.0
> C1 1.4 C1 1.3
> C2 2.5 C2 2.1
> C3 1.5 C3 1.4
> C4 1.7 C4 1.5
> C5 5.5
> 14.1 MHz Bypass =1.0
> C5 2.6
> C6 5.2
> 7.05 MHz Bypass =1.0
> C6=1.7
> C7=3.9
> C8=10.9
> ----------------------------------------------------------
> Not sure if the C2 anomaly is relevant to 160/80 M
>
> 73 de Brian/K3KO
>
> On 7/25/2016 18:11 PM, Don Wilhelm wrote:
>> Brian,
>>
>> You might try going into the KAT3 menu and go through the L1-L8 and
>> C1-C8 settings to hear the relays click with each selection.
>>
>> If all the relays are working, you should be able to do a check on the
>> health of the inductors and capacitors using a method similar to that
>> shown for the KAT100 in the right column of page 35 - manually select
>> the inductors starting with L1 and see what the SWR is on a high band.
>> With each other inductor, the SWR should increase. Change to a lower
>> band if the SWR gets too high to indicate (highest is 9.9). Do the same
>> for the capacitors.
>>
>> I have not tried this technique with the KAT3 (but it should work) - I
>> have used it with the KAT100 and the KAT2.
>>
>> 73,
>> Don W3FPR
>>