[TowerTalk] Lightning Protection

[K8RI]

On 7/8/2013 3:17 PM, Jim Lux wrote:
> 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...)

IIRC It's in the hand book, I'll see if it's in the current edition i 
have on the computer


>
> 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.
>

The multi length ground is an operational ground and not a safety ground 
for lightening.

For a lightening pulse that could mean thousands of volts.

Although we think of lightening as static, it is not DC.  The sharp rise 
and fall times mean it's much more like medium frequency with most of 
the energy lying near, or in 160 meters. OTOH Lightening strokes are 
pretty much unique with no two being identical.

> 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.

Not necessarily.  Even large aircraft have received substantial damage 
from strikes while airborne and some have been brought down.

I've never had a plane struck, but coming back from Denver in the 
Debonair, I had such a static build up, all the radios quit working and 
I had to power down the whole panel and reset to get them back up.

ATC was kinda excited when I came back on as they had lost the 
transponder return.  They understood when I explained.  I had to do a 
reset twice in that area.  Man, what a ride!  Flying blind in that stuff 
(all the electronic instruments quit!) is exciting.  It's like partial 
panel while on a roller coaster and no visibility.


73

Roger (K8RI)