[Elecraft] my KPA1500 and 160M

[w5sum at comcast.net]

This morning I put up a W7FG true ladder line 160M doublet.   Upon testing, 
the K3 internal atu does great, matches at 1.3:1.  But when I throw the 
KAP1500 in line, it gets all pissed off, throws up and faults out.  Says SWR 
is 99:1 !!!

The Antenna:  The Apex is at 50'.  It is in a inverted Vee config, with both 
ends approx 20' off the ground.   I'm using 59' of the 600 ohm true ladder 
line to a Balun Designs 5KW 4:1 Balun. This is fed with 22' of Wilson LMR400

Both the K3 internal atu, AND the KPA1500 internal atu get a great match on 
80M, 1.2:1   with no issues.

Honestly, most of the work on 160M is FT8 running 20 watts or less, so just 
using the K3 to get a successful match on 160M is fine

I just wonder why the KAP1500 doesn't like the same antenna the K3 likes.

Any ideas here fellers?

thanks and 73

73 and GL OM DE w5sum