[Elecraft] K3S - High SWR on 6 Meters

[Keith Trinity WE6R]

Jim;
Make sure you are updated to the latest 5.67 Firmware.
In the notes of the K3 Utility you will find this in the Help\K3 
Firmware Release Notes;
It is specific for 6m, it is -only- for the KPA3"A", and will fix any 
oscillation issues (which can manifest as High-SWR);
Keith WE6R Elecraft K3/K4 Tech

K3 MCU 5.67 / DSP 2.88 / FPF 1.26, 1-22-2019
* 6 M GAIN REDUCTION (FOR USE WITH KPA3A):
In some cases the KPA3A may have more gain than necessary on 6 meters. 
As a precaution, all radios using a KPA3A (instead of the older KPA3) 
should be configured to insert some attenuation. See instructions below. 
No hardware modifications are required.

INSTRUCTIONS:  [Do this only on a K3S, or a K3 that has a KPA3A installed.]
1. Select the 6 meter band.
2. Connect a dummy load rated at 50 W (or higher) to the transceiver.
3. Set the PWR control to 50 watts.
4. Place the ATU in bypass mode.
5. Locate the CONFIG:TUN PWR menu entry. Set the value to NOR using VFO A.
6. Locate the CONFIG:TXGN HP menu entry.
7. Tap the '8' switch (NR) once to add "ATN6" to the parameter display 
on VFO A.
     (Tapping it a second time would return to the original 
non-attenuated setting.)
8. Exit the menu.
9. Hold TUNE to do automatic power calibration on 6 meters at the 50 W 
level. After a few seconds, tap XMIT to terminate the TUNE operation.

NOTE: If you have difficulty reaching full power on 6 meters after 
making this change, it could be because your PA module is actually a 
KPA3, not a KPA3A. In this case, re-do the above procedure, changing the 
TXGN HP menu setting back to the original (i.e., without "ATN6" 
showing). (Max. power output at 50 MHz is specified at 100 W +/- 1 dB, 
typical. 1 dB below 100 W is approx. 90 W. See Specifications for max 
output at 51 MHz and higher.)