So, I have built myself a go-kit and am having a problem with high SWR on it's 2M/70CM antenna. Here are the specs:
Radio: Icom 7000
Feedline: 18" of LMR400 with Amphenol Silver Plated PL-259s
Mount: directly on a 2" UHF barrel fed through Go-kit's top
Antenna: Diamond CR270 2M/70CM
SWR readings (per an MFJ HF/VHF/UHF antenna analyzer):
420MHz 2.1 SWR
lowest point on 70CM band - 437MHz at 1.5 SWR
450MHz 2.3 SWR
On 2M the SWR is 6.3 at both ends of the band (after manually tuning the antenna for lowest SWR) with not much better in between.
Most of the time this station will not have access to an earth ground, so I have a common "chassis ground" for the antenna tuner and the radio. When I first encountered SWR problems I guessed that grounding was the issue, so I added an 8 inch bit of antenna line connecting it to the chassis ground (as can be seen in the picture). This seems to have little effect. If I touch the antenna while checking the SWR on in the 2M band it drops from 6.3 SWR to about 4.2 SWR.
Here is a picture:
What do I need to do to fix this?