[TowerTalk] Lighting protection for roof mounted tower

[Roger (K8RI)]

First I've been retired for about 14 years, but in industry (and on old 
barns no less) they installed lightning rods. They were all tied 
together by a very heavy braided Copper cable of may be 0 or 00 size. At 
the end the cables would run down the edge of the roof, down the corner 
of the building to ground rods at each corner. Industry still does 
something similar, just more elaborate. That grounding system can drive 
sensors located all over the building crazy that work in the micro and 
milli volt range.

On 5/13/2010 12:36 AM, Ray wrote:
> I have an 8 ft roof tower that I am debating where and how to install. My
> concern is lighting protection and the way I would like to run the coax.
> This roof tower will hold a 3 el 6m yagi, small yagis for 2m and 440mhz, and
> a 2m vertical on top. My radio room in almost in the center of the house.
> The run for all my HF coax and cables from the station to the Single Point
> Ground is about 30 ft long running under the raised floor. We do get late
> summer monsoon rains and lightning.
>
> First option: mount the roof tower above my shack. I would run the coax
> cables and #4 grounding wire straight down, through the roof and attic and
> into a living room divider wall with a 90 degree sweep to my shack. The coax
> run would be about 30 ft. There are #4 ground wires both in the attic and
> raised floor that I could connect the roof tower ground wire to.
>    
Were I to choose this method (which I wouldn't) you need to remember you 
are channeling any strike to the tower and antennas right through the 
middle of your house.  Lightning does not like to make turns so it'd 
likely get off at or before that 90 degree sweep. I just have an 
aversion to channeling lightning any where *through* my house. I'd also 
use a much larger ground wire.
>
> Second option: mount the roof tower at about the same place and run the coax
> to the edge of the roof, down to ground level, then into my SPG. The total
> RG8 coax run for each antenna and ground wire would be about 85 ft. This
> length of coax can start to lead to losses on the VHF frequencies.
>
>    
I'd probably choose this route and follow both the pattern of the old 
lightning rods with the cable from the tower down the rids to each end 
and then down to the ground system at each corner, plus I'd also run a 
larger ground (maybe #2 or even larger) along with the antenna cables to 
the bulkhead and SPG.  If you are really concerned about the loss in 85 
feet you might consider something like LMR-600 or even some Hard line 
such as 3/4, 7/8, or even 1" plus, but anything over the 600 at that 
length for only 440 is a bit of overkill IMHO.

Although I've been running 228' of LMR 400 to both a pair of 11L 440 
antennas and 12L 144 antennas successfully I'm now switching to 
LMR-600.  A bit over a year ago I was able to pick up about 1500 feet of 
LMR-600 for $1.20 USD per foot which is not much more than early 9913 
cost. A bit of shopping will still find it under $1.50 USD per foot.  
OTOH the connectors run about $13.00 USD each.

As I have an SO2R set up, but with multiple operator positions I chose 
to standardize on one coax and one type of connector. I do have two 
exceptions.  I use RG-8X for the runs to the 40 meter, half wave, center 
fed, sloping dipoles, and Davis BuryFlex(TM) for rotator loops. BuryFlex 
is very rugged and flexible with loss characteristics similar to 
LMR-400. My preference for connectors is crimp and I use them entirely 
*EXCEPT* for the UHF to fit LMR-600. They are made but run some where 
between $60 and $80 each so I settled for clamp type there.

73 and good luck...I'm sure you will find many opinions

Roger (K8RI)

> My concern is about running the roof tower cables thru the house thereby
> creating a possible lightning path into the house vs. making the longer
> cable runs to the SPG. I do have two 70 ft HF towers nearby with quite an
> extensive ground system on each. All ground rods (about 50) are
> interconnected with #4 wire to each tower, the SPG and the house mains
> input. The roof tower would be somewhat dwarfed by the two HF towers, but
> when lighting strikes, we all know that it will go anywhere and everywhere.
>
> What are the thoughts, comments and opinions about bringing my 6m and VHF
> cables through the house? I would sure like the shorter coax runs, but
> safety is my concern.
>
> Tnx,
>
> Ray,
> N6VR
>
> Chino Valley, AZ
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