The mysteries of tuning a random wire

Dave W0DCX

Here is another antenna tuning conundrum.  This morning I hoisted up a 72-foot random wire (and deployed a counterpoise).  My calculations suggested it should tune great on 30 meters (almost exactly 3/4 wavelength) but poorly on 40 or 20 meters (close to 1/2 wave multiples).  Here is what I found in terms of SWR of the untuned antenna as determined by my NanoVNA and what I observed when I tried to achieve a good SWR match with my KX2 automatic antenna tuner.

30 meters - VNA SWR = 2.3; KX2 can tune to SWR = 1.0  : NICE!
20 meters - VNA SWR = 13.17; KX2 can tune to SWR = 1.0 : NICE BUT SURPRISED!
40 meters - VNA SWR = 4.4; KX2 can only tune to SWR = 4.4 : TOTALLY BAFFLED - WHY?

Any insights?
Dave W0DCX

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