[time-nuts] GPS antenna selection - lightning

Bob Camp kb8tq at n1k.org
Mon Aug 8 11:13:24 EDT 2016


Hi

We tend to look at all this lighting / EMP stuff very much as a “get to the ground” 
sort of thing. For whatever reason the whole thought process stops once we get
to a coper weld rod driven however far into the dirt. 

If you try to operate a vertical antenna against that same rod in the middle of a nice dry
summer.  You will quickly find out that dirt != ground. The same fun and games
that get you a low impedance ground for your antenna also apply to a low impedance 
ground for your protection system. Its not an identical process, but it’s the same idea. 

You can argue that a good bond of everything to a single point is sufficient. Looking around
my house, there is most certainly *not* a single point of entry for everything. Various 
utilities and other wires / chunks of conductive stuff go off in a variety of directions. Like
most homes in the US, it’s a wood frame structure. There is no nice steel frame to 
tie everything to. I suppose the first step would be to tear the house down and re-build
it from scratch …..

Bob

> On Aug 8, 2016, at 10:00 AM, jimlux <jimlux at earthlink.net> wrote:
> 
> On 8/7/16 8:06 PM, Bill Hawkins wrote:
>> This thread grows old, so here's one person's summary:
>> Marine supply stores sell rolls of 4 inch
>> wide copper strap for connecting the mast on the wheelhouse cabin with
>> the keel of fiberglass boats. This is also the ground for all electronic
>> equipment. The strap is considerably less inductive than a wire.
> 
> No - strap is about the same inductance as a wire of the same length. The advantage of strap is a lower RF resistance, which is important if the strap is part of your antenna system, because it's less resistive loss than a wire.
> 
> For lightning impulses, either conducted or radiated, the inductance dominates the voltage rise (e.g. Xl is much larger than Rac).
> 
> Strap or bar may be easier to make connections to (drill a hole in some 1/8x1" bar, tap it, and hook your lug up)
> 
> 
> 
> 
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