[Elecraft] K3 #281 Perceived Output Issue

[Ian Kahn]

Several people offered some very good suggestions and asked several valid
questions about my testing. Here are answers to many of those questions:

1. The meter I'm using in the test is a known-good MFJ-815B HF power/SWR
meter.
2. I'm using a known-good 300W dummy load for my "antenna", so any
reflected power is minimal, as is SWR.
3. I do have the internal ATU installed, but it is in BYPASS, as I have a
resonant antenna on 20m-10m and use the KAT500 for 40m/80m, or when I run
power.
4. Test results at lower power levels:

10m 10w out - 10w on meter; 25w out - 19-20w on meter; 50w out - ~30w on
meter
12m 10w out - 10w on meter; 25w out - 20w on meter; 50w out - 30w on meter
15m 10w out - 10w on meter; 25w out - 20w on meter; 50w out - 35w on meter
17m 10w out - 10w on meter; 25w out - 20w on meter; 50w out - 35w on meter
20m 10w out - 10w on meter; 25w out - 20w on meter; 50w out - 40w on meter
40m 10w out - 10w on meter; 25w out - 20w on meter; 50w out - 40w on meter
80m 10w out - 10w on meter; 25w out - 20w on meter; 50w out - 40w on meter

I also ran the TX Gain Calibration from the K3 utility one more time, with
a different cable. Here are the results of that calibration (note - I
didn't run the milliwatt calibration because I don't use a transverter with
the IF Out. It just goes to my P3):

K3 Tx Gain Calibration data written on 2016-02-23 at 22:18:30
K3 Serial Number 00281
K3 MCU revision 05.38. RS-232 speed 38400 bit/s.
Elecraft K3 Utility Revision 1.15.8.18
1900 kHz TxGain LP  52
3750 kHz TxGain LP  30
5336 kHz TxGain LP  56
7150 kHz TxGain LP  46
10125 kHz TxGain LP  52
14200 kHz TxGain LP  23
18110 kHz TxGain LP  24
21200 kHz TxGain LP  19
24930 kHz TxGain LP  25
29000 kHz TxGain LP  30
52000 kHz TxGain LP  24
1900 kHz TxGain HP  46
3750 kHz TxGain HP  48
5336 kHz TxGain HP  87
7150 kHz TxGain HP  62
10125 kHz TxGain HP  58
14200 kHz TxGain HP  28
18110 kHz TxGain HP  21
21200 kHz TxGain HP  18
24930 kHz TxGain HP  18
29000 kHz TxGain HP  27
52000 kHz TxGain HP  13

After running the TX Gain Calibration again, I checked the above output
numbers, and they stay the same. It seems as if I am losing about 20% of my
output power for any setting above 10w, except on 10m, where at 100w I seem
to be losing about 50w. It also seems as if maybe there is an issue with
the internal 100w PA, based strictly on my observations and a wild guess.
If there are any other suggestions/recommendations, I'm all ears. If not,
the next step is an email to the good folks in Aptos.

Thanks and 73,

--Ian
Ian Kahn, KM4IK
Roswell, GA  EM74ua
km4ik.ian at gmail.com
10-10 #74624  North Georgia Chapter #2038
PODXS 070 #1962
K3 #281, P3 #688 KAT500 #860, KPA500 #1468

On Mon, Feb 22, 2016 at 5:40 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> Ian,
>
> Try TX Gain Calibration again - use a different coax jumper between the K3
> and dummy load - that could possibly be faulty.  If that does not correct
> it, contact Elecraft support.
>
> 73,
> Don W3FPR
>
>
> On 2/22/2016 5:29 PM, Ian Kahn wrote:
>
> Don,
>
> I upgraded the MCU and ran the TX Gain Calibration at that time,
> successfully. I also ran it again Friday night, while testing, to make sure
> that wasn't the issue. It ran successfully both times.
>
> Thanks.
>
> Ian, KM4IK
> On Feb 22, 2016 5:24 PM, "Don Wilhelm" <w3fpr at embarqmail.com> wrote:
>
>> Ian,
>>
>> Did you upgrade after MCU version from 5.13 or below to 5.14 or greater?
>> That requires you to do the TX Gain Calibration (see 5.14 Release
>> Notes).  K3 Utility makes the task easy - just connect a dummy load that is
>> good for 1.8 to 54 MHz and capable of 50 watts or greater and the process
>> is automatic - follow the prompts in K3 Utility, it will take only about 2
>> minutes to complete after the dummy load is in place.
>>
>> If K3 Utility fails the TX Gain, there is one more chance - do each band
>> manually (see the Calibration part of the manual).
>>
>> If that does not correct it, contact support.
>>
>> 73,
>> Don W3FPR
>>
>>
>> On 2/22/2016 11:21 AM, Ian Kahn wrote:
>>
>>> Reposting, since this didn't seem to get out when I originally sent it
>>> last
>>> Friday evening. If you get this a second time, please forgive the noise.
>>>
>>> Thanks and 73,
>>>
>>> --Ian
>>> Ian Kahn, KM4IK
>>> Roswell, GA  EM74ua
>>> km4ik.ian at gmail.com
>>> 10-10 #74624  North Georgia Chapter #2038
>>> PODXS 070 #1962
>>> K3 #281, P3 #688 KAT500 #860, KPA500 #1468
>>>
>>> ---------- Forwarded message ----------
>>> From: Ian Kahn <km4ik.ian at gmail.com>
>>> Date: Fri, Feb 19, 2016 at 10:37 PM
>>> Subject: [Elecraft][K3] K3 #281 Perceived Output Issue
>>> To: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net>
>>>
>>>
>>> All,
>>>
>>> I have what I think is an output issue with my K3 s/n 281. When set at
>>> 100W
>>> output, I am getting the following approximate output values:
>>>
>>> 10m     ~55w
>>> 12m     ~40w
>>> 15m     ~50w
>>> 17m     ~60w
>>> 20m     ~60w
>>> 40m     ~70w
>>> 80m     ~70w
>>> 160m    ~70w
>>>
>>>
>>>
>>
>