So I've been running an HT clipped to my visor for like two years now and finally broke down and bought a proper mobile rig — picked up a Yaesu FTM-300DR a few weeks ago and spent most of last weekend doing the install. Overall pretty happy with how it turned out but I have a couple things bugging me.

First one is the antenna. I went with a NMO mount drilled through the roof, ran the coax down the A-pillar and under the dash. Used some LMR-400 I had laying around from a previous project. The SWR is reading fine on 2m, like 1.3:1 or so, but on 70cm it's climbing up around 2.2:1 and I'm not totally sure if that's the antenna or maybe how I routed the coax. It's a Diamond NR770H if anyone's familiar with it.

Second thing is just noise. I get some kind of whine that tracks with engine RPM on receive, not super loud but annoying enough that I notice it. I haven't chased it down yet. The radio is powered off a fused run direct to the battery which I thought would help but apparently not.

Anybody dealt with either of these? The SWR thing is what's really on my mind because I want to make sure I'm not cooking the finals on 70cm before I do any serious operating.

The RPM whine is almost certainly alternator noise getting in through the power leads or a ground loop somewhere. Try adding a ferrite choke on the power cable right near where it connects to the radio — snap-on type works fine. Also check that your radio chassis has a solid ground to the vehicle body, not just relying on the negative lead. Sometimes running a short bonding strap from the radio bracket to a nearby chassis ground point kills it completely. I chased that same noise on my FTM-400 for a week before I realized the ground on my power connector was a little loose.

On the 70cm SWR — the NR770H is a decent antenna and 2.2:1 isnt terrible, you're not gonna hurt anything at that level, but it could probably be better. Sometimes those dual band antennas are a little finicky and the connector end or how the coax is dressed near the mount can affect UHF more than VHF. Make sure your NMO connector is torqued down properly and there's no moisture getting in. LMR-400 is overkill for a mobile run but it certainly won't hurt anything.

congrats on getting a real radio in there, big difference from running an HT off the visor lol. i had almost the exact same whine issue in my jeep and what fixed it for me was one of those cheap noise filters inline on the power feed — i think i paid like 8 bucks for it on amazon. not the most elegant solution but it works. some guys swear by just finding the real cause but i never had the patience for that.

as for the 70cm swr honestly i wouldnt lose sleep over 2.2 especially if youre mostly on 2m. but if it bugs you try reseating the antenna on the mount, sometimes they dont make perfect contact right away especially if you used any kind of thread locking compound or the mount wasnt totally clean when you drilled it.