I'm in the "something's fishy" camp on this one.
RE: cable loss, was that test done with the antenna attached? I thought cable-loss tests had to be done into an open or a short. How can the tester tell what it's seeing is the result of the cable or the load at the end of the cable, if not? In any case, the 440 loss should be about twice as much as the 2-meter loss, and neither should be very high with only 15' of cable.
RE: putting a spring in the antenna, I know the PNW trails well so I know the trees you're talking about. It looks like you did a decent job accommodating the antenna length, but I don't know if it's really necessary. The Larson antennas are pretty durable and stand up to considerable abuse. On the trail, you're probably not exactly DX-ing, so you might consider 2 antennas: 1 stubby antenna for the trail and a longer one (the 2/70) for the road or trails that are less tree-lined. I have a 12" antenna on the roof of my RAV4 and it seems to do almost as good a job as an antenna 3x as long in most cases. More precisely, the antenna that's 3x as long doesn't pull in 3x more signal or distance.
But, if you have a 2:1 VSWR or less as measured at the radio end of the cable, I'd call it good and go wheelin'.
Ya you're right, CL needs to be done into a short or open. Sad that I forgot that, guess I've been in the office too long.
M6GOM, we do indeed have some "operator error" going on here.
So my cable loss traces are crap, but the VSWR and Return Loss sweeps should be valid.
A short antenna for the woods may not be a bad idea. I was hoping for a set it and forget it sort of setup. I had the spring from my NMO150 setup on my last jeep so thought I'd use it. Of course my 2/70 is too short now without a spring.
I'll check out my spring and see if its causing issues too.
Thanks for the feedback everyone, we'll see what I find.