[TowerTalk] Lightning Protection

[Jim Lux]

On 7/8/13 9:37 AM, K8RI wrote:
> On 7/8/2013 10:33 AM, Jim Lux wrote:
>> On 7/8/13 7:18 AM, john at kk9a.com wrote:
>>> I also have a shack on the 2nd floor and I also disconnect all cables
>>> going to the tower. I only use the station for major contests so doing
>>> this is not really inconvenient. Disconnecting however is not a reliable
>>> means of protection as the energy can be induced into anything nearby. I
>>> am not sure if there is any way to stop this from occurring. Even if you
>>> disconnect it is a good practice to have multiple lines of ground rods a
>>> single point ground and MOVs or GDTs on every rotator and relay.
>>>
>>> John KK9A
>>>
>>
>>
>> I'm not sure about the value of the multiple lines of ground rods *from
>> the entrance panel*.  I just don't see the physics of what it's doing
>> there.  The goal at an entrance panel is to have everything tied to one
>> reference voltage, and let that go up and down.
>
> That is for operating on multiple bands to prevent the rig from rising
> too far above ground  Recommended by ARRL.
>
Exactly where is this recommended by the ARRL (so I can go find it...)

Is that the "tuned ground wire" thing? where you put half a wavelength 
at each band of interest, on the assumption that a transmission line 
repeats the far end impedance at every half wave.

I don't think that has any validity for lightning (and it's dubious for 
Tx or Rx, as well).

What you're concerned about, presumably, is that the coax ground isn't 
too different from the equipment chassis ground.  That's easy: a 
reasonably short wire between equipment and coax entry point.

I don't know that the voltage of the chassis, relative to some distant 
point outside, has a lot of importance.   After all, planes have no 
ground wire or rod, get hit by lightning, and keep on working.


I think there's an enormous amount of almost correct info about 
grounding out there. Some of it dates from the days of running a single 
long wire against a ground rod. Some of it is from electrical codes 
(which have different objectives). Some of it is just plain 
misunderstanding of the physics, but has crept into the lore.

(that sharp bends have much more inductance than gentle ones... provably 
wrong, but you see it in lots of places)