so i've had this FT-857D sitting on the shelf for like 8 months and finally got around to doing a proper mobile install in my F-150. ran the power leads direct to the battery with an inline fuse, got a Diamond NR770HB on the roof with a NMO mount, feed line is about 12 feet of LMR-240 going through the firewall with a rubber grommet. everything looks clean honestly im pretty happy with how it came out.

but here's the thing - SWR on 70cm is great, reads like 1.3:1 across the whole band which seems fine. but on 2m i'm getting like 2.1:1 around 146 MHz and it gets worse toward the edges. antenna is supposed to be pre-tuned so i didnt expect to have to do anything. i havent trimmed anything yet. is this normal for that antenna or did i mess something up with the mount? the NMO hole is centered on the roof pretty much.

also the radio itself seems to work fine, making contacts on the local repeaters no problem, just bugging me that the meter shows that SWR and i dont want to cook the finals over time.

The NR770HB is a decent antenna but they do sometimes need a little trimming to get 2m dialed in, especially on a large vehicle like a full size truck. The roof gives you a great ground plane which is good but sometimes that actually shifts resonance slightly compared to how the manufacturer tested it. Try trimming just a tiny bit off the top element - like 2-3mm at a time and recheck. At 2.1:1 you're not really hurting anything with the 857's protection circuits but yeah better to get it right.

Also double check that NMO connector is making solid contact and the coax isn't kinked anywhere near the mount. I've seen bad SWR readings that turned out to be nothing more than a loose center pin on the NMO. Worth 5 minutes to check before you start cutting.

had basically the same thing happen with mine, diferent antenna but same deal where 70cm was fine and 2m was off. ended up being a tiny nick in the coax where it went through the firewall grommet, wasnt enough to see visually but was causing all kinds of weirdness. just something to check while youre poking around in there