[Antennas] Dumb question?

[Joe Giacobello]

This subject was discussed in depth on the TowerTalk forum some time 
ago.  I also believed at the time that lightning rods and porcupines 
discharged the atmosphere in their vicinity and, in so doing, reduced 
the probability of a strike.  I was corrected by K1TTT, who apparently 
has a lot of professional experience in this area, and a paper written 
by a professor of E.E. from the New Mexico Inst. of Mining and 
Technology.  The paper was tellingly entitled "There Is No Magic To 
Lightning Protection: Charge Transfer Systems Do Not Prevent Lightning 
Strikes."  (If you can't find the paper on the Web, I'll be happy to 
e-mail a copy.  It's easy reading.)

The primary purpose of mounting a lightning rod on a house or other 
structure appears to be to simply offer a preferred path to ground for 
the strike, as opposed to its using the structure itself as the path.

73, Joe
K2XX



Bill Aycock wrote:
> Ron-
> Prepare for strong differences of opinion. Many will say that charge 
> dissipation is a myth, and many will say it works. I tend to be on the 'it 
> works' side, based on experience working for 38 years in a Rocket fuel plant 
> where all buildings were made to Army Ordnance standards. These standards 
> include "Uffer" grounds and pointed rods above.
> In that time, we only had one lightning induced fire, and that was 
> attributed to a painting crew having disconnected the overhead system, and 
> not re-connecting it.
> Bill-W4BSG
>
> ----- Original Message ----- 
> From: <bonddaleena at aol.com>
> To: <antennas at mailman.qth.net>
> Sent: Sunday, May 17, 2009 3:00 PM
> Subject: [Antennas] Dumb question?
>
>
>   
>> Hi, here is a question I would like to put before the list....
>>
>> I have just finished getting my 2 - 95 foot towers up. They are well
>> engineered and guyed VERY well with 1/4" EHS guy wire.
>> The towers are well grounded with low imped copper strap from each leg
>> to a system of 8' ground rods all interconnected.
>> I have had tall towers like this at my last 4 QTHs and never had a
>> problem with lightning DIRECTLY hitting a tower. I have had some 'near
>> misses' which have taken out several mast mounted VHF and UHF GaaSFET
>> preamps , until I learned how to protect them.
>>
>> However, I was watching a special last night on Ben Franklin and they
>> went into great detail about how he invented the 'lightning rod'
>> concept.
>> I have read extensively about this subject, but still have this
>> question on my shrinking mind:
>>
>> Since I leave near the thunderstorm capitol of the USA (Florida), would
>> I gain any safety by installing a very pointed conductor at the very
>> top of my tower's mast?
>>
>> One tower will have a pair of 432 MHz long yagis at 115'. They will be
>> fed with 7/8" CATV hardline and have the preamp near the rotor.
>> I have ground straps to bypass the rotor. The antennas are all at DC
>> ground, so there would be a direct path to ground for everything on the
>> tower.
>>
>> My feeling is that by placing a sharply pointed 'tip' to the top of the
>> mast will help dissipate a charge before it builds to strike potential.
>> As you are aware, this is how Ben's stuff works. Lightning rods cannot
>> withstand a direct 'hit'. They are for dissipation purposes.
>>
>> OR, am I inviting a strike with the pointy rod????
>>
>> I've not seen this topic discussed before.
>>
>> Thank you in advance.
>>
>> ron
>> N4UE
>> ______________________________________________________________
>> Antennas mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/antennas
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Antennas at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>>
>>     
>
>
> ______________________________________________________________
> Antennas mailing list
> Home: http://mailman.qth.net/mailman/listinfo/antennas
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Antennas at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
>