Re: K3 SSB + CW Power Overshoot

[Elecraft mailing list]

The K3 SSB + CW Power Overshoot behavior has been passed up the Elecraft Tech/Engineering chain.  I expect it may take them some time to get to it, so in the meantime it would be useful for those interested to conduct the test below to determine if the behavior is unique to my K3 or more wide spread. 
 
My primary concern is operating with the K3 driving an amplifier (KPA 500 in my case).  It is often the case that the overshoot is so high that the KPA faults on the first key press when power is set for 500 watts and in SSB +CW mode.
__________________________________________________________________________________
 
Following is a repeatable test that exhibits the overshoot and power adjust instability problem we have been discussing.
 
Setup:
1,  Output terminated in dummy load (ANT 1)
2.  Config: CW WGHT -- [1]  SSB +CW
3.  S Meter Peak -- ON
4.  Meter Mode -- SWR/RF (to observe output power)
5.  Set Power 50 watts (initial setting)
6.  Select any band
 
Operation:
1.  Select CW mode; VOX on
 
Press key and hold.
    Note that power ramps up to the set 50 watt value
    Adjust power up or down; note that the power change is smooth with no jumps or overshoots
    Press key on/off/on .... -- power always returns to set value
    Release key and set power to 50 watts
 
2.  Change to SSB mode (upper or lower)
 
    Press key and hold while observing watt meter -- note that power overshoots the 50 watt level and then             drops to 50 watts.
    Adjust power up.  Note that the power jumps high then returns to set value. 

    Adjust power down.  Note that the power jumps high, than returns to set value.
    (note that whether the power is adjusted higher or lower, the output power jumps higher, then                reduces to the set value).
    Also note that the power supply current jumps (overshoots high) coincident with each power adjustment.
    Release key, then press again and hold. Note that the power does not overshoot the set value.  Release and     hold any number of times and power continues to be stable at set value.
 
Changing now to CW mode with VOX and power is stable.
Changing back to SSB +CW and power is unstable and with overshoot with first key press.
 
This phenomenon occurs in both HP and LP modes.
This phenomenon is apparent when the K3 is initially turned on from a cold start, but gets progressively more pronounced after about 10 minutes of on time in quiescent state (no RF out).  PA Temp at this time is 25C.  As requested, fan is set to level 1.
 
Discussion:
It is my understanding from old Reflector mail posts that the SSB +CW mode is implemented such that when key is pressed, the K3 changes dynamically from SSB to CW mode.  It appears that the CW ALC function is not in play until some time delay after key press, at which time the CW output settles at the set power level.  This time delay would appear to be at the root of the problem.  When the power is adjusted, it would appear the ALC loop opens up and then re-engages when adjustment stops.

 
The fact that the phenomenon changes in magnitude as the K3 warms up, may simply be a function of linear stages within the ALC loop changing gain with temperature.
 
The above test sequence is easy to apply and as such would be very curious to see if the phenomenon occurs on any of the Elecraft bench test K3's.
______________________________________________________________________________________
 
Thanks and 73,
Dan AC6DM
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[Paul Baldock]

It seems I can get a much better SWR by manually changing the L/C
settings. However, I have not figured out how to store those manually
entered settings; it always returns to the auto setting (as
demonstrated by changing bands and then changing back ).

Anybody know how to do this?

- Paul  KW7Y

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[Jim Brown-10]

On 6/16/2018 9:16 AM, Dan Maase via Elecraft wrote:
> Changing back to SSB +CW

What is SSB +CW?

73, Jim K9YC

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[Elecraft mailing list]

> Changing back to SSB +CW 

What is SSB +CW? 
 
73, Jim K9YC 
_________________________ 

Jim:

SSB +CW is a mode/configuration whereby one can send CW when in the SSB mode.  The CW frequency is offset from the SSB carrier frequency by the value of the selected CW side tone.  Purpose:  enables means to reply to a SSB communication with CW in poor band conditions.   
Sometimes termed "cross mode". 

73, 
Dan AC6DM
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[K9MA]

I've also noticed that the ATU often doesn't get a very good match, even
if I try twice as per the manual.  The K3 ATU, by contrast, usually
finds a much better match for the same load.  (Not talking high load SWR
here, less than 2:1.)  I haven't compared the component values in the
two ATU's, but I expect they're similar, so they should be able to
achieve equally good matches.

Scott K9MA


On 6/16/2018 12:07, Paul Baldock wrote:

> It seems I can get a much better SWR by manually changing the L/C
> settings. However, I have not figured out how to store those manually
> entered settings; it always returns to the auto setting (as
> demonstrated by changing bands and then changing back ).
>
> Anybody know how to do this?
>
> - Paul  KW7Y
>
> ______________________________________________________________
> Elecraft mailing list
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>
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--
Scott  K9MA

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[wayne burdick]

Scott,

Every ATU design has different stray amounts of L and C. But the differences are small between the KPA1500 ATU and our other ATUs, especially the battlefield-proven KAT500, which has a virtually identical circuit. We test the ATUs into various loads to verify matching range.

That said, if you believe yours has a matching range problem, please contact support. There’s even the possibility it’s a firmware issue.

73,
Wayne
N6KR



> On Jun 16, 2018, at 1:26 PM, K9MA <[hidden email]> wrote:
>
> I've also noticed that the ATU often doesn't get a very good match, even if I try twice as per the manual.  The K3 ATU, by contrast, usually finds a much better match for the same load.  (Not talking high load SWR here, less than 2:1.)  I haven't compared the component values in the two ATU's, but I expect they're similar, so they should be able to achieve equally good matches.
>
> Scott K9MA



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[K9MA]

Thanks, Wayne.

73,
Scott K9MA

On 6/16/2018 16:35, Wayne Burdick wrote:

> Scott,
>
> Every ATU design has different stray amounts of L and C. But the differences are small between the KPA1500 ATU and our other ATUs, especially the battlefield-proven KAT500, which has a virtually identical circuit. We test the ATUs into various loads to verify matching range.
>
> That said, if you believe yours has a matching range problem, please contact support. There’s even the possibility it’s a firmware issue.
>
> 73,
> Wayne
> N6KR
>
>
>
>> On Jun 16, 2018, at 1:26 PM, K9MA <[hidden email]> wrote:
>>
>> I've also noticed that the ATU often doesn't get a very good match, even if I try twice as per the manual.  The K3 ATU, by contrast, usually finds a much better match for the same load.  (Not talking high load SWR here, less than 2:1.)  I haven't compared the component values in the two ATU's, but I expect they're similar, so they should be able to achieve equally good matches.
>>
>> Scott K9MA
>
>

--
Scott  K9MA

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