[TowerTalk] Ground Radials Insulated or Not

[Gary Schafer]

Jim Lux wrote:
> At 08:18 AM 12/6/2004 -0800, Michael Tope wrote:
> 
>> From a performance point of view, I suspect it doesn't make
>> any difference at all whether the wires are insulated or not.
>> One consideration that I haven't heard discussed with regard
>> to radials, however,  is lightning protection. Wouldn't it be better
>> from a lightning perspective to have at least some of the radials
>> in the system uninsulated? Perhaps a few heavy radials (6 to 8)
>> made from #4 bare copper interspersed with the balance of the
>> radial system made from whatever is cheapest. Just a thought.
>>
>> Mike, W4EF......................................
> 
> 
> One might argue that you want to keep the "RF grounding" function of the 
> antenna (which, after all, is connected to the coax shield) separate 
> from the "lightning current discharge" function.

How are you going to keep them separate?

> 
> The junction from antenna/tower/whathaveyou to the lightning ground is 
> going to rise in voltage pretty substantially, regardless of how good 
> the ground is. A notional 5 ohm ground with 10kA lightning stroke 
> current is going to go to 50 kV.

That's right! The lightning is not going to discriminate between 
anything that you want to call a lightning ground and the radials that 
are in the ground that you call an rf ground.

Why not take advantage of all that work of putting in radials. That is 
one of the best lightning grounds you can get. It provides many paths 
for the lightning to dissipate. Much better than several ground rods.

However it would not hurt to install a few ground rods connected to the 
radials in addition.

> 
> I'll have to look for the details, but I seem to recall that one of the 
> analyses that NEC-4/NEC-3 were designed for was to look at whether 
> lightning grounds should be combined with RF grounds (particularly 
> radial fields).  I do recall that they came up with the surprising 
> finding that with elevated radials, the performance with the radial 
> field connected to the ground stake was worse than with them separate.
> 

That would make sense as an elevated radial system is done to isolate it 
from ground losses.

73
Gary  K4FMX

> Jim, W6RMK
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