Topband: RFI - and lots of it (negative fuse)

[Tom W8JI]

> My Icom radios come with the power cord fused for both negative and
> positive.  From what you say, I should remove the negative fuse if I 
> install
> the radios in a vehicle.  Now when the radios are at the fixed station the
> same power cord is used (both lines fused), I understand that the negative
> line fuse should also be removed.
>

The standard from UK is well worded:

"4.6.4. Negative Feed Connection
In the case of negative earth return vehicles, the negative power line 
should not be fused. It should be connected to the vehicle body as close as 
practical to the point at which the battery-to-body connection is made. Do 
not connect the negative power line directly to the battery.
For heavy commercial vehicles (>7.5Tonne GVW) only, and those vehicles with 
tilting cabs where the cab may be isolated from the chassis by rubber 
mountings, a ground point is provided by the vehicle manufacturer within the 
cab to provide battery to cab grounding. Generally this is located within 
the main fuse box. It is recommended that this point be used for 
installations in this instance.  With certain equipment it may be necessary 
to connect the negative supply line to a local earth point. In this case an 
existing vehicle earth point must be used."

I just went through terrible problems with an aftermarket EFI system that 
insisted on a battery negative connection. It never worked properly until I 
used the vehicle chassis as the negative.

I regret now, after years of experience with problems, ever following the US 
and Japanese standard of using a battery negative pole or terminal, and not 
the vehicle chassis.  I still, because the warnings to use the battery 
negative were so strong in an expensive EFI system, I followed it (knowing 
better) and had a ground loop noise problem right away.

I've damaged radios and accessory equipment several times over the years, 
and the ground loop also makes common mode noise and audio hum and noise 
problems worse. I used to buy into the common advice, because I never really 
thought about it. No negative fuse holder for me, and no negative battery 
post connections for me. My three wire plug shack power supplies have all 
been modified now, and no longer have a ground loop from mains or station 
ground to the negative power lead.

The UK standards have it correct.

73 Tom