K2/100, KAT100 strange tuning problem

[Solosko, Robert B (Bob)]

Hello All,

        I hope that someone can suggest where to start tracing down a
rather strange tuning problem that cropped up in the middle of working
the IARU on Saturday. The short description is that the K2/100-KAT100
stopped tuning in AUTO mode when in high power mode on 40 meters. Here's
some of the details:

1 - Tuning with the K2/100 and KAT100 on 40 meters has worked fine since
I completed the KPA100 (rev. D) 6 months ago.

2 - I had no problems tuning for about the first 10 QSOs on 40m, and
then the rig suddenly wouldn't tune at all when in high power mode
(there were no lightening strikes during that time) - then tuning became
erratic.

3 - Tuning worked fine when the power was reduced to low power mode: all
I had to do was reduce the power just to the point where the power LEDs
on the KAT100 switched from high power to low power and everything
worked fine - then increasing the power just to the point where the
power LEDs on the KAT1200 switched from low power to high power and the
KAT100 wouldn't tune at all.

4 - If I tuned in low power mode, then cranked up the power to 100w, the
rig transmitted just fine (and I made a bunch more 40m QSOs working like
that)

5 - The rig tuned just fine in high power mode on all other bands.

6 - The problem doesn't seem to an antenna problem as the same thing
happens when the antenna is replaced with a dummy load.

The KAT100 manual has an obscure comment under troubleshooting that
says: "Erratic tuning in AUTO mode: This is much more likely to occur at
high power, and could be due to high RF voltages on the K2 chassis, mic,
key, power supply leads, or KAT100 control cable. First, try reducing
power to 10 watts or less. This will force auto-tune to be done at 2
watts. If this cures the problem, you may need to add RF bypassing to
your power supply, key, or mic; improve your ground system; move the
antenna farther away; or use a "choke balun" between the ATU and the
transceiver." --

That actually doesn't tell me much about where to start looking, since
the everything has been working for 6 months (OK, I did get the new MH2
mic, but that was several weeks ago and it's been working fine), and
everything worked for at least the first 1/2 hour on 40m in the IARU, so
nothing's that I changed that could account for the sudden lack in
ability to tune in high power mode on 40m.

Help! Where do I start looking for the cause?

Thanks in advance.

Bob W1SRB

       
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[Don Wilhelm-3]

Bob,

There is nothing unique to 40 meters in the KAT100, *but*.

Behavior like that *could* be related to a parasitic oscillation in the
KPA100.  The parasitic usually revealed itself during a TUNE operation
with the KAT100 also installed.

The KPA100 T/R switch was re-designed to address that very problem.  If
your KPA100 was ordered before last December, it has the old T/R switch
in it, and can have the parasitic problem on 40.

I suggest you promptly obtain the KPA100UPKT and install it in your KPA100.

73,
Don W3FPR

Solosko, Robert B (Bob) wrote:

> Hello All,
>
> I hope that someone can suggest where to start tracing down a
> rather strange tuning problem that cropped up in the middle of working
> the IARU on Saturday. The short description is that the K2/100-KAT100
> stopped tuning in AUTO mode when in high power mode on 40 meters. Here's
> some of the details:
>
> 1 - Tuning with the K2/100 and KAT100 on 40 meters has worked fine since
> I completed the KPA100 (rev. D) 6 months ago.
>
> 2 - I had no problems tuning for about the first 10 QSOs on 40m, and
> then the rig suddenly wouldn't tune at all when in high power mode
> (there were no lightening strikes during that time) - then tuning became
> erratic.
>
> 3 - Tuning worked fine when the power was reduced to low power mode: all
> I had to do was reduce the power just to the point where the power LEDs
> on the KAT100 switched from high power to low power and everything
> worked fine - then increasing the power just to the point where the
> power LEDs on the KAT1200 switched from low power to high power and the
> KAT100 wouldn't tune at all.
>

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[Solosko, Robert B (Bob)]

Thanks Don... My KPA100 was ordered in December and is Rev D, so it's
the version with the 40m parasitic problem fixed (it doesn't have RFC 10
on the antenna connector that the earlier versions did)- I wonder if the
change to Rev D didn't quite fix the problem. Rev. E came out shortly
after I built my KPA100, but I don't know what changed from D to E. Are
there other things that I should check?

Thanks.

Bob
W1SRB


-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Monday, July 16, 2007 11:17 AM
To: Solosko, Robert B (Bob)
Cc: [hidden email]
Subject: Re: [Elecraft] K2/100, KAT100 strange tuning problem

Bob,

There is nothing unique to 40 meters in the KAT100, *but*.

Behavior like that *could* be related to a parasitic oscillation in the
KPA100.  The parasitic usually revealed itself during a TUNE operation
with the KAT100 also installed.

The KPA100 T/R switch was re-designed to address that very problem.  If
your KPA100 was ordered before last December, it has the old T/R switch
in it, and can have the parasitic problem on 40.

I suggest you promptly obtain the KPA100UPKT and install it in your
KPA100.

73,
Don W3FPR

Solosko, Robert B (Bob) wrote:
> Hello All,
>
> I hope that someone can suggest where to start tracing down a
rather

> strange tuning problem that cropped up in the middle of working the
> IARU on Saturday. The short description is that the K2/100-KAT100
> stopped tuning in AUTO mode when in high power mode on 40 meters.
> Here's some of the details:
>
> 1 - Tuning with the K2/100 and KAT100 on 40 meters has worked fine
> since I completed the KPA100 (rev. D) 6 months ago.
>
> 2 - I had no problems tuning for about the first 10 QSOs on 40m, and
> then the rig suddenly wouldn't tune at all when in high power mode
> (there were no lightening strikes during that time) - then tuning
> became erratic.
>
> 3 - Tuning worked fine when the power was reduced to low power mode:
> all I had to do was reduce the power just to the point where the power

> LEDs on the KAT100 switched from high power to low power and
> everything worked fine - then increasing the power just to the point
> where the power LEDs on the KAT1200 switched from low power to high
> power and the KAT100 wouldn't tune at all.
>
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[Don Wilhelm-3]

Bob,

Since you do have early updated version of the KPA100 - there is one
thing yet to check, and that is the value of C31.  If it is not a .22 uf
capacitor, it should be changed to the new value.  Elecraft will supply
one if you ask - the part number is E530295.

The capacitor situation was not discovered until after the updated
KPA100s began shipping.  Under certain conditions the updated KPA100
will oscillate near 600 kHz with the lower value capacitor at C31.

I know this is confusing - the older KPA100s had a 40 meter parasitic,
likely caused by RFC10 while the newer version has this other
oscillation problem if the bypass capacitor is not large enough.
Similar outward behavior, but entirely different causes.

BTW - the changes from 'D to E' were only to clean up the manual.  There
is only a loose link between the manual level and the hardware revision
level.

73,
Don W3FPR

Solosko, Robert B (Bob) wrote:
> Thanks Don... My KPA100 was ordered in December and is Rev D, so it's
> the version with the 40m parasitic problem fixed (it doesn't have RFC 10
> on the antenna connector that the earlier versions did)- I wonder if the
> change to Rev D didn't quite fix the problem. Rev. E came out shortly
> after I built my KPA100, but I don't know what changed from D to E. Are
> there other things that I should check?
>
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[Solosko, Robert B (Bob)]

Thanks Don,

        That could be the problem - my Rev D manual says it .033uf. I'll
check it out and see it that cures the problem.

        Thanks again.

Bob

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Monday, July 16, 2007 12:32 PM
To: Solosko, Robert B (Bob)
Cc: [hidden email]
Subject: Re: [Elecraft] K2/100, KAT100 strange tuning problem

Bob,

Since you do have early updated version of the KPA100 - there is one
thing yet to check, and that is the value of C31.  If it is not a .22 uf
capacitor, it should be changed to the new value.  Elecraft will supply
one if you ask - the part number is E530295.

The capacitor situation was not discovered until after the updated
KPA100s began shipping.  Under certain conditions the updated KPA100
will oscillate near 600 kHz with the lower value capacitor at C31.

I know this is confusing - the older KPA100s had a 40 meter parasitic,
likely caused by RFC10 while the newer version has this other
oscillation problem if the bypass capacitor is not large enough.
Similar outward behavior, but entirely different causes.

BTW - the changes from 'D to E' were only to clean up the manual.  There
is only a loose link between the manual level and the hardware revision
level.

73,
Don W3FPR

Solosko, Robert B (Bob) wrote:
> Thanks Don... My KPA100 was ordered in December and is Rev D, so it's
> the version with the 40m parasitic problem fixed (it doesn't have RFC
> 10 on the antenna connector that the earlier versions did)- I wonder
> if the change to Rev D didn't quite fix the problem. Rev. E came out
> shortly after I built my KPA100, but I don't know what changed from D
> to E. Are there other things that I should check?
>
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