[Elecraft] KX3 ATU interaction with LDG ATU

[Owen Mehegan]

Hello, I have an original LDG Z-11 Pro tuner which I used to use with my 
K2, and a KX3 with internal ATU. Recently I set up an HF doublet at home 
after being off-air here for a few years. I found that the KX3 ATU could 
only tune the antenna to about 2.4:1 on 40 meters, but it was below 2:1 
on 30-10 meters. I thought I would try the LDG instead. I put the LDG in 
line, put the KX3 tuner in bypass, and tuned again. The LDG did a better 
job on 40, bringing SWR to 1.5:1, but some  of the higher bands were a 
bit worse - around 2:1. So I thought, "What if I use the LDG for 40 
meters and the KX3 for higher bands?" Here's the strange thing: I tried 
putting the LDG tuner into bypass and setting it to semi-auto tuning, 
and using the KX3 ATU again. When I did that, I got 1:1 SWR on 40m. Yet 
when I unplug the LDG completely and plug the antenna directly into the 
KX3, I'm back to 2.4:1 on 40m. My question is, why does it seem like 
having the LDG tuner in line is affecting the SWR seen by the KX3, even 
if it is in bypass (I realize I should only be using one tuner at a 
time)? Maybe this is more of an LDG question, and I've sent it to them 
as well, but thought I might as well ask the brain trust here. Thanks!