Thanks Jerry. Yes, that will work quite well.
And to all that wonder, it will make little if any difference if the
attenuator output is open, terminated into 50 ohms or shorted. It will
show the characteristic impedance. With 100 watts into the input there
will be about 0.1 watts at the output. That reflected back to the input
and thus attenuated 30 dB will be then about 0.0001 watts of reflected
power. That gives and SWR of 1.002:1. (If I did the math correctly.)
73
Bob, K4TAX
On 3/17/2025 5:31 PM, jerry wrote:
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<rmcg...@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-requ...@mailman.qth.net wrote:
Message: 5
Date: Sun, 16 Mar 2025 15:00:09 -0700
From: Corky<af...@searlsnet.com>
To:Elecraft@mailman.qth.net
Subject: [Elecraft] Perplexing output power behavior for K3(s)
Message-ID:<5f4487fc-7b18-4ab3-a2aa-354312c93...@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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