Totally in agreement with Keith. I observe slow ramp up of power on
the 1st transmission after making a band change or power change.
But I add; when measuring power, be sure the dummy load is actually 50
ohms non-reactive. Just because it says so on the label, is it? I
have 4 different ones and none of the 4 are actually 50 ohms
non-reactive. They are 48, 52, 55, and 59 ohms with some small amount
of reactance, yet all were labeled "50 ohms". Two purchased new by me
and never operated at or exceeded rated power vs. time.
And with power meters, they are calibrated for full scale with a 50 ohm
non-reactive load. Any power measurement made by not using a 50 ohm
non-reactive load is mostly a "close enough" measurement +/- 10% or so.
Typically the LP-100 by Telepost is a bit different in that it
measures voltage on the line and current in the line and does the
calculation for power. Thus these are more accurate over a range of
load impedance variations.
73
Bob, K4TAX
Message: 1
Date: Wed, 15 Sep 2021 16:12:45 -0700
From: Keith Trinity WE6R<ke...@elecraft.com>
To:Elecraft@mailman.qth.net
Subject: Re: [Elecraft] K3 transmitter power woes
Message-ID:<272f2f48-af0d-88e5-d8a0-ef591ea76...@elecraft.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Hi Chet;
You should be able to run the TX gain cals with no errors, otherwise
something is wrong.
NOTE; After a successful Gain-Cal, then never, ever, TX at exactly 5 or
50watts (or 1.0MW) as that can cause an inadvertent TX gain cal and mess
it up.
To me, it would appear the LPA is weak.
Check your Watt-Meter Cal, or make sure your WM LP is around 65-100 and
WM HP is 25-55 typically.
Then if you can get the gain cals to run, send me the numbers, IE click
Display TX Gain Summary and cut and paste.
*However, I just noticed you mentioned the MW gain cal has issues, so it
could be before the LPA/KPA and would be the Band Pass Filter adjustable
caps.
Also from my notes;
Slow ramp up of power, mainly on the upper bands,? can be D1 E560040
burnt (or bad solder joint) and/or bad Q6 E580026 on LPA. (power ramps
up starting very low). If Q6 shorts, it can take out Q3 E580030.
**REPLACE D1*and* Q6 if the solder joint is bad!!!
Fix; Replace ALL THREE at same time! Q3, Q6 & D1 on LPA.
Note; This can also just be normal operation of Firm Ware overshoot
protection. (power goes quickly to near (~80%) desired power, then ramps
up the final percentage in seconds. This happens if you; 1. Change
desired power, 2. Change bands, 3. Power cycle radio.
So, set desired power, then long press XMIT to do a TUNE (with TUN PWR
at nor), or Key up on FM (if you have a FM filter). The go back to your
desired mode and it should reach good power quickly.
Keith WE6R Elecraft K3/K4 Tech.
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