[TowerTalk] FIRST TOWER & 2ND FLOOR SHACK --HELP

[K8RI]

On 8/7/2013 1:56 PM, Jim Brown wrote:
> On 8/7/2013 9:59 AM, Earl Morse wrote:
>>   Whether you run the conduit to the top of the tower and put your
>> polyphasers at that point OR run the conduit to the base of the tower
>> and place the polyphasers at that point OR run conduit through the
>> house and place the polyphasers at the entrance point its all about
>> providing that alternate path for lightning that doesn't pass through
>> your hamshack.
>
> It DOES matter where Polyphasers are located -- their function is to
> protect the equipment to which they are connected, and they work by
> shorting the center conductor of the coax to the shield. For that
> reason, they should be as close to the equipment as practical.
>
> That is VERY separate from the issue of grounding, which is the most
> critical aspect of lightning protection. I think most experts would
> advise that the cables go down the tower all the way to its base, be
> bonded to the tower at the top and bottom, and go along or in the ground
> to the house, where they should be bonded to the building ground, then
> come up to the shack. There must also be a bond from your shack ground
> to the building ground.

Another aspect of grounding the shield at the top and bottom of the 
tower as well as at your SPG at the base of the house is the 
considerable capacitance from the center conductor to ground/shield in 
that length of coax. I believe this tends to bypass much of the pulse 
coming down the line "before" it reaches the rigs, so theoretically‎ 
it's not only better for the rigs but reduces the work the Polyphasers 
have to do.

73

Roger (K8RI)

>
> The tower itself must be grounded at its base, both to it's own concrete
> base (a Ufer ground) and to at least three rods, usually each bonded to
> a leg.  This provides a short (low inductance) path to earth for a
> strike, which minimizes what is coupled to your home.
>
> Remember -- lightning is not a DC event, it is an RF event, with its
> energy broadly centered around 1 MHz, and extending for at least one
> decade of frequency above and below. (that is, 100 kHz to 10 MHz). So
> what matters most is the inductance and the routing of the grounding
> conductors, not their resistance. And remember also that lightning comes
> into our homes from the power system, the telephone system, CATV
> systems, and on the wiring in our homes, so all of this stuff must be
> bonded together and to that central ground, usually at the point were
> power comes into the house.
>
> Finally, radios do not need "an RF ground" to work, to be safe, or to
> minimize noise or RFI.  But they DO need proper bonding, as I've
> described for lightning safety, and proper bonding can often help with
> noise and RFI.
>
> 73, Jim K9YC
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