Why run power from battery dirrect?

[KF5LJW]

High power radios that have floating grounds can develope some screwy problems that can cause interfearince with automotive electronics.

I see what they are saying but I don't agree with their management of the power negative lead.

FWIW I agree with you on these two points.

1. To prevent any interference with the auto Electronics regardless if the radio is floating or not is to go to the point where the battery terminates to the vehicle. Typically they have 2 termination points. 1 to the alternator and another to the engine block, and another smaller one to the firewall. Use the one with the heaviest cable.

2. I completely disagree with fusing the negative lead. If for some reason the fuse were to open, would cause the return current to flow through something it is not suppose to like the coax shield or mic cable. In which case would likely burn open a solder tract inside the radio. The negative should be a solid made connection whether or not you take it to the battery or the chassis.

Personally when I did installs in the 80's after High Energy Ignitions and ECM came out, we used a special battery replacement bolt distributed by Motorola. It replaced the factory battery bolts for side mounted battery post. I did litterally hundreds of Law Enforcement vehicles and worked closely with the auto and radio manufactures. I was even published in a trade magazine called Mobile Radio Technology for reducing noise interference in mobile installations in about 1984. (I think it was 1984, been a long time). It was my MSEE thesis paper in college.

Most of today's vehicles now come with a factory battery term plate on both the battery post with an empty stud positions to facilitate high power accessory equipment terminations like two-way radios and high power stereos.

[M0GVZ]

Minimizing RF interference to and from the vehicle's sensitive electronic circuitry is one good reason.

I usually run just one heavy line to the battery + terminal with a fuse block right at that point (at the battery) and use the vehicle's chassis as the current return path. Of course, that depends on getting a very good electrical connection to the chassis/frame somewhere, which in some vehicles isn't so obvious.

In my new car I won't be powering the Icom 7000 from a direct connection to the battery. There is a fuse box below the rear light which is there to run towbar electrics, aux trailer and the heated seats - none of which I have. The cable feeding it is rated at least 125A as thats the max total of the fuse ratings. Somehow I don't think it'll have a problem running a 23A radio. The aux trailer electrics fuse alone is rated at 30A. I'll run the ground from the floorpan in the boot (trunk). Doubt I'll have any issues as I've not had any in the past running the ground from near the radio rather than from the battery.

I never have any common mode issues because I'm not frightened to take a drill to the car.

[AD5MB]

That amount of drop seems excessive. That is roughly equivalent to a single 14g wire 20 feet long.

painted panels held together by bolts that were lubricated and are trending to dusty and rusty.