Total posts : 45366
Several decades of taking care of AM broadcast station antenna systems has given me a healthy respect for “unwanted” electrical potential and discharge. I have spent hundreds of sleepless evenings putting antenna networks and transmitters back together after lightning and static discharge do their work. I have even repaired the destruction these forces can impose on FM stations as well.
” Local electrical codes require grounding of masts and grounded protection of lead wires (such as spark gaps or gas discharge tubes) at the point of entry of a building because this provides a path to ground in the event of a direct or nearby strike. The idea here is to protect the building and its contents, and NOT the mast or antenna. I wanted to make that distinction about the purpose of protective grounding.” -Neil
I wish local electrical codes took into consideration what happens when you have RF potential at the end of a needle pointing into the sky. Simply put, they don’t. I have wrestled for decades with code policy makers to understand the basic theory of adding high frequency RF energy into the equation. Discharge tubes, static chokes and other such devices, when used in an RF environment, become, at best, fuses that burn and arc themselves. Been there, repaired it, own the shirts. I have many stories (I won’t bore you with them) about protection devices failing and spending hours finding why the transmitter won’t go back on the air. Instead, you get the annoying “chunk-a-chunk-a” sound of the transmitter trying to reset. Broadcast techs know exactly “the” sound I mean.
Lightning, interestingly enough, does not propagate from clouds in the sky. Instead, a lightning strike intiates from an object on the ground. Knowing this should change how you deal with lightning. Many radio practitioners have no idea about how a lightning strike develops. However, they really should take the time, instead of just cleaning up the mess. Its all about saving time and money, isn’t it?
The most reliable lightning/safety ground known to man is a 2-4 inch copperstrap from the antenna support to well-designed dissapative ground. Strap is used due to the low inductive reactance to ground. Lightning and static dischrages are very high frequency oscillating arcs. The grounding rules for Part 15 are short sided and incomplete not allowing for safe operation of an elevated “radio needle” charged with RF ready and willing to intiate a real disaster.
So, for someone who has had to deal, on many occasions, with the destructive power of mother nature, I suggest safety, in any venue, should be foremeost. And in CFR 47, this is referred to as “good engineering practice”.
Marshall Johnson, Sr.
Rhema Radio – The Word In Worship