[Elecraft] KX3 atu anomalies - or it is me.

[Phil&Debbie]

“...I use an LDG tuner at a remote location from my rig. I see something similar to what is being discussed at times. Sometimes it will stop tuning (perhaps quickly) when it gets a match slightly below 2:1. Other times I get a much better match...”

Don’t forget that unless your transmission system out to the remote tuner is perfect, you will see a composite SWR that could be better or worse than the remote tuned SWR (and Murphy says it will be worse!).  To determine the SWR range you can see, terminate your transmission system at the remote tuner input with a good load and record the SWR.  Lets call this SWRa.  Most autotuners stop tuning when the SWR is at or below below 1.5:1.  So now, depending on the relative phases of the mismatched systems, your SWR range measured in the shack can be:

Max SWR = SWRa X 1.5
Min SWR = SWRa/1.5 or 1.5/SWRa (whichever gives you the larger numerator).

So as an example, let’s say your terminated transmission system has an SWR of 1.3:1 on a given frequency.  This could easily be the case (or worse) assuming you have switches, jumper cables, etc in-line.   Then if you assume the autotuner tunes to an SWR of 1.5:1, the maximum SWR you could see in the shack could be 1.95:1, and the minimum SWR you could see would be 1.15:1.

So when you do a remote re-tune, the phase of the reflected signal as well as the tuned SWR could both be different resulting in very different in-shack SWR readings.  So you really can’t always blame the remote tuner for not seeing a good in-shack SWR unless your transmission system is very good.

Phil – AD5X