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

[Bob McGraw]

Barry:

Yes, see page 52  for 5 watt calibration and page 53 for 50 watt 
calibration in the Elecraft manual.

Based on that information this clearly says "Set power to exactly 5.0 
watts"  Then hold "TUNE".  VFO B should show about 5 W.   Tap XMIT to 
exit TUNE.  Clearly as Keith at  Elecraft has written more than one, 
"Avoid using exactly 5.0 watts and 50.0 watts unless you are performing 
an automatic transmit gain calibration.

Now where all this gets off-base, if you have an antenna connected, 
which we all know will not be 50 ohms and X =0, and the calibration 
routine is initiated, the calibration routine will run with some strange 
combination of impedance/load.    Therefore, to correctly perform a TX 
Gain calibration, it should ONLY be done with a known good 50 ohm 
non-reactive load.   And it must be done on all bands 160M - 6M.

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).

 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
>> ______________________________________________________________
>> Elecraft mailing list
>> Home:http://mailman.qth.net/mailman/listinfo/elecraft
>> Help:http://mailman.qth.net/mmfaq.htm
>> Post:mailto:Elecraft at mailman.qth.net
>>
>> This list hosted by:http://www.qsl.net
>> Please help support this email list:http://www.qsl.net/donate.html
>> Message delivered tobbaines at mac.com