Posted by Ken Kopp-3 on URL: http://elecraft.85.s1.nabble.com/K3-and-the-subreceiver-tp4593879p4598805.html
I use the 2nd receiver ... almost without exception ... to keep
an ear on 6M to catch band openings. It's only antenna route
is from the BNC connector on the rear.
I also have an AlphaDelta 80-10M dipole for general listening
on the 2nd RX if needed.