I'm getting unexpected SWR readings on my new Diamond X510HDM collinear. At 2 meters I'm seeing 2.1:1 at 146.520 and 1.8:1 at 147.000, which seems high for this antenna. At 70cm it's closer to spec at 1.4:1 around 445 MHz. Has anyone experienced similar issues with the X510HDM? I'm using RG-8X with proper PL-259 connectors, antenna is mounted at 25 feet on a push-up mast with good ground radials. The installation looks clean and weatherproofing is proper. Any thoughts on what might be causing the elevated 2M SWR?

Check your coax connections first - PL-259s are notorious for poor solder joints that create intermittent high SWR. Also verify the antenna is truly vertical and clear of metal objects within several feet on all sides.

I had similar issues with mine until I discovered water had gotten into the matching network at the base. Even though it looked weatherproofed, moisture was causing detuning on 2M specifically.

Your readings actually aren't that far off spec for the X510HDM - Diamond rates it at <1.5:1 but real-world installations often see slightly higher SWR due to ground interactions and mounting variables. Try temporarily raising it another 5-10 feet to see if ground coupling is the culprit.