Topband: Wireless Internet RFI Issue

[Jim Brown]

On 7/29/2013 11:11 AM, Tom W8JI wrote:
> That almost always is a switching power supply issue. The normal mode 
> of excitation is differential between the power mains and other 
> cables. My neighbor's system bothered me.
>
> The BEST solution

is to replace the switching PSU with a linear PSU having a suitably 
voltage and current rating.  Most of us have a box full of these vintage 
wall warts laying around, and if we don't, they're easy to buy cheap at 
thrift stores and hamfest flea markets.

The only tricky part is mating with whatever connector the equipment mfr 
has chosen to use for power. I solve that by cutting both PSU cables and 
installing Power Pole connectors on the one coming from the linear PSU 
and the one with the equipment power connector.

If, for one reason or another, I can't do that, I plug the switcher into 
one of several outlet boxes that I've built with a Corcom or Delta RF 
filter.

> to this is a lightning protection type outlet strip that (if it does 
> not have them) you add capacitors to. I used a system that had F 
> connectors, eithernet, telco, and power.

Lightning protection type outlet strips have MOVs, and MOVs used in this 
manner are often the CAUSE of lightning damage if things plugged into 
them are interconnected with equipment grounded at a different point, 
even when the equipment at the other outlet also is "protected" by an 
MOV. . Examples where this can be a problem are computers at different 
locations connected by Ethernet cables, computers connected to radios 
(which must be bonded to station ground), etc.  The problem within a 
station can be avoided by bonding between all of the interconnected 
equipment and the station ground with short, fat copper, but that won't 
help with stuff plugged into an outlet strip plugged into a different 
wall outlet.

Ah, you say, all those green wires are bonded together back at the 
breaker panel, and the panel is grounded.  Yep, but there's lots of 
inductance in those connections, and a bit of resistance, so when the 
MOV shoves the lightning spike onto the green wire(s), the potential 
difference between interconnected equipment can easily be enough to fry 
that gear in a lightning event.  We learned about that in the pro audio 
world almost 20 years ago, and I've seen many reports of damage to 
computers connected by wired Ethernet.

73, Jim K9YC