[Elecraft] Perplexing output power behavior for K3(s)

[jerry]

On 2025-03-17 14:36, Bob McGraw wrote:
> 
> Now the reason for stressing known good 50 ohm load, I have 3
> different brands, and power dummy loads.    Although all say "50 ohms"
> they are not!  One is 57 ohms (air type load),  one is 48 ohms cold
> and 53 ohms hot (Cantenna) , and the third is 50.5 ohms (Bird 100 watt
> load).
> 
*** And I have a 500W Bird 30dB attenuator that I use as a dummy load.  
Just measured it -
50.5 ohms, with nothing connected at the output end.

                - Jerry, KF6VB


> From the Messages files, 9/21/21, #35799 I find:
> 
> Keith_WE6R
> 09/21/21#35799 // <https://groups.io/g/Elecraft-K3/message/35799>
> 
> 
> Hi Glenn;
> I understand you got it going, but;
> What exactly did you do when you;   "Did reset on K3.." ?
> A Parameter Initialization (EE-INIT)  will wipe many settings and 
> calibrations.
> 
> *Also, one should never TX at exactly 5 or 50 watts (or 1.0MW) as you
> might do an inadvertent manual Transmit-Gain-Calibration.*
> 
> Keith WE6R Elecraft K3/K4 Tech.
> 
> Hope this answers your questions.
> 
> 73
> Bob, K4TAX
> 
> 
> <https://groups.io/g/Elecraft-K3/topic/85741710?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2CWE6R+TX+Gain%2C20%2C2%2C20%2C85741710%2Cct%253D1&ct=1#window-192949176>
> //
> <https://groups.io/g/Elecraft-K3/topic/85741710?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2CWE6R+TX+Gain%2C20%2C2%2C20%2C85741710%2Cct%253D1&ct=1#>
> 
> 
> 
> On 3/17/2025 3:02 PM, Barry Baines wrote:
>> Bob:
>> 
>>> On Mar 17, 2025, at 11:20, Bob McGraw<rmcgraw at benlomand.net> wrote:
>>> 
>>> Corky:
>>> 
>>> I'd say the radio needs a transmit power calibration.   The K3 
>>> Utility makes this easy.  Only a known good 50 ohm dummy load is 
>>> required.  Preferably connected direct to the radio output, bypassing 
>>> any switching, etc.
>>> 
>>> NEVER NEVER set the power to 50 watts!  This is the point of 
>>> automatic power calibration.  Thus avoid 5 watts and 50 watts as 
>>> power settings.  Use either 4 or 6 watts and 40 or 60 watts for your 
>>> normal operation.  Cold has nothing to do with it.
>> This is a very interesting admonition and is something that I wasn’t 
>> aware of.  Could you point me to Elecraft documentation (or where Fred 
>> Cady, KE7X may discuss this in his K3 book)  that explains automatic 
>> power calibration and using the 5W and 50W power settings only for 
>> calibration?
>> 
>> Thanks,
>> 
>> Barry, WD4ASW/5
>> Keller, TX
>> 
>>> 73
>>> 
>>> Bob, K4TAX
>>> 
>>> 
>>> On 3/17/2025 11:00 AM,elecraft-request at mailman.qth.net wrote:
>>>> Message: 5
>>>> Date: Sun, 16 Mar 2025 15:00:09 -0700
>>>> From: Corky<af4pm at searlsnet.com>
>>>> To:Elecraft at mailman.qth.net
>>>> Subject: [Elecraft] Perplexing output power behavior for K3(s)
>>>> Message-ID:<5f4487fc-7b18-4ab3-a2aa-354312c93a05 at app.fastmail.com>
>>>> Content-Type: text/plain
>>>> 
>>>> I have an older K3 that has been upgraded to a K3S with the output 
>>>> power modification for the P3. All this works, but I find that when 
>>>> I turn on the radio and then transmit on 20 m, the first TX is 
>>>> always about 1/2 power compared to the second and all future TX 
>>>> episodes. This only seems to happen when I turn on the radio and it 
>>>> is "cold" meaning at room temperature. I only have numbers for 20m, 
>>>> but when I did the first TX today, the output was just under 40 W 
>>>> PEP with the power set at 50W. The second TX (about 2 min later) the 
>>>> output power was 78 W PEP and this persisted for all TX for the next 
>>>> hour. Nothing was changed in the radio between the first and second 
>>>> TX episodes.
>>>> 
>>>> I do not remember ever seeing this behavior with the original 
>>>> boards, but it appears as though something is "warming up" before it 
>>>> will transmit at full power. Does anyone have any insight as to what 
>>>> might be happening and whether this is something I need to address 
>>>> or just live with?
>>>> 
>>>> Thanks and 73,
>>>> -Corky, AF4PM
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