Topband: 160m L impedance??

[John]

OK Gurus......

Quarter-wave L, vertical to 66 feet, balance horizontal.  32 radials on the ground, length ranging from 35 to 68 feet with a good mix of those lengths.  Using 14 solid copper, insulated wire.  At the feed point, I see the lowest SWR of 3.2 at 1.820 MHz.  But, the impedance measures 80 +/- ohms!  I see 7 mh and 1050 pf.  

At the shack end using 75 feet of BuryFlex, I measure lowest SWR of 1.2 at the same freq, 1.820.  The impedance there measures 60 ohms.  I used both my Autek RF-1 and MFJ-259.  I have no BC stations within 10 miles or so.  My soil is mostly sand, although it is a top soil, sand mix. 

The "bad" news is the antenna works OK....128 in two seasons.

Why the high impedance?  

Thanks, and 73...........John K4NP   (this should bring on some beauts)