2M Antenna Mast Question

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Doug Rathman:
Just to get started, here is a minimal ground plan.   See the ARRL antenna book chapter #1 for some common sense on this.

1) Ground the antenna mast to a ground rod driven beside it.  Brass ground pipe clamps, bury grade rod clamps, and #4 solid wire.  

2) Ground the coax to the same rod if it's also beside your house entry point. Otherwise drive in another rod.  A Polyphaser device (or other makes) work okay. If you can't afford one of these devices then at least ground it using an SO239 female/female barrel connector and a 1/2" brass waterpipe clamp hooked right to the ground wire near the rod.

3) Ground your radio and power supply chassis with some heavy flexible wire (maybe some #10 automotive hookup wire or coax braid) to a small piece of copper pipe connected to the back of your desk.  Use stainless steel hose clamps. Don't daisy chain your equipment.

4) Run some of that braid or #10 wire from the pipe on the back of your desk outside to the ground rod. Maybe double up on that run.

5) Daisy chain the rods together with the #4 solid wire then also to your main AC service panel ground rod (or waterpipe if you have an older house) so that everything is bonded together properly.   Keep your ground connections reasonably short and avoid sharp turns.

6) I recommend using a 2-postion coax switch that is grounded to your copper pipe bus behind the desk, so it's easy disconnect.

Having fun yet? :-)

73, Doug NG0K

Chris J. Smith:
"And dont get me started by saying "If you take a direct lightning strike everything will be toast anyhow" Because if you follow the right bonding/grounding procedures, You CAN take direct lightning strikes with no damage!"

There may be no damage from the lightning strike to the mast or the antennas, but have you thought about the heat from the strike itself?  Even if the strike is dissapated by the lightning protection, the nearness of the installation to the house may cause heat/fire damage to the house.

Since the main reason for the elaborate lightning protection is the draining of static charges to PREVENT lightning from striking, you may do well to rethink your statement of 'no damage from lightning strikes' to such an installation.  Nature and its actions can't be predicted.

Kenneth Meyer:
Quote:  "There may be no damage from the lightning strike to the mast or the antennas, but have you thought about the heat from the strike itself? Even if the strike is dissapated by the lightning protection, the nearness of the installation to the house may cause heat/fire damage to the house.

Since the main reason for the elaborate lightning protection is the draining of static charges to PREVENT lightning from striking, you may do well to rethink your statement of 'no damage from lightning strikes' to such an installation. Nature and its actions can't be predicted".  

The "heat" from the point of attachment of lightning to a mast or antenna is at that point ONLY.
It is pretty silly to think that 20 or so feet away there would be any heat from the very short duration of a direct lightning strike.

In the "olden" days, Lightning rods for roof protection were about 3 feet tall, Just because of that very fear.  Since the 1950's or so it was found that 12 inch rods are PLENTY long enough to protect a roof!

Lightning protection is a pretty well defined science nowadays.  
Most anything CAN be properly protected from lightning damage. It is only a question of effort (And cost) to do so.

This has been proven time and again on tall building
(Skyscraper) type buildings with antennas at roof level. The ONLY heat is right at the point of attachment.

 
 

Chris J. Smith:
That may be so Ken, but the point is can you guarantee the lightning strike will follow the mast to the ground?  No--nobody can.  Most professional installations keep the mast or tower away from buildings just because the lightning charge may jump.  Therefore the heat damage may be closer than you may think since heat would be produced at the point the lightning charge leaves the mast and at the point in 'attaches' itself to another structure.  

There is NO predicting the actions of nature, and the person who states they can is a fool.  Since the gentleman stated the mast would actually be attached to his house, it is wise to assume a worst case scenario and plan for it.

Kenneth Meyer:
Lightning protection rods (Air terminals) are attached directly to a roof to protect it! The Bare copper (Or aluminum) cable is attached directly to the building.
Has been done this way for over 100 years now.
The procedure to properly install lightning protection on buildings is well established.   Lightning WILL follow that mast, Or lightning ground cables. ANY metalic object within 6 feet NEEDS TO BE BONDED to the down conductor.
This is done to prevent any "flashover" during a direct strike.
A good comparison of what happens when lightning strikes a metalic object like an antenna mast is just like dragging an arc welding electrode across the mast.
The heat developed, And the marks on the mast look almost exactly the same.
AND lightning bolts are not all the same size, energy, or duration. some are very small and weak, Some can be very large and powerful, (And longer in duration if a number of strokes takes place)  Some of the largest strokes can actually burn little holes into an aluminum antenna mast.
I have masts and antenna elements here from the top of very tall commercial towers that look like a person "held" that arc welder in one place for 5 seconds or so and burned holes.
That point of attachment is the only place there is any heat, In a properly protected installation.
While there can be other points of attachment at the same time, When everything is installed right, NO damage results.
The 6 foot "rule" is for normal installations. Critical
installations like military ammunition dumps, High level government buildings, etc. Most everything is bonded to ground, No matter the distance to the mast or down conductor.

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