Here is a little primer on lightning:
Having your antenna grounded does not drain off any charge that helps prevent a strike. As a matter of fact grounding the antenna makes it slightly more prone to a strike but not grounding it is much worse as you have no control over what path the energy will take if not grounded. When a storm cloud moves over the area charge builds on objects on the ground. The ground items, towers etc start to emit streamers. When a strike is imminent step leaders come down from the charged cloud and move in approximately 150 foot steps. Changing directions with each step. When a step leader gets close enough to a streamer a connection is made. What follows is a plasma trail which is a very low impedance path that the lightning charge follows. Lightning can be thought of as a current source. In other words if there is a 10 KA strike it is going to develop that much current into whatever it strikes. If for example it hits your tower and the total impedance to ground is quite low then the voltage developed across the tower will be relatively low. But if the ground system is not a good one then the voltage will rise higher. It will still develop the 10 KA current. Bonding all equipment to a common point is one of the first steps to take. Just adding a polyphaser coax protector to the coax line will only equalize the current between center conductor and shield. If power is not protected and everything bonded together the coax protector will do little good. Even without a coax protector, just bonding everything is a great first step. The whole idea is to keep everything at the same voltage level when a strike occurs. 73 Gary K4FMX _____ From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Tony KT9AC Sent: Wednesday, August 18, 2010 9:25 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Polyphaser Question Remember the objective is not to take the brunt of a lightning strike, but to drain off any static that would attract that strike. Lightning is just a spark looking to close the gap, and if your antenna is closer to DC ground, it will find something closer to its potential (i.e. static charged) to hit. Any protection is better than nothing, and don't scrimp on buying the cheapest used protector. Its your equipment your protecting and potentially avoiding liability. I buy new Polyphasers for our site and sleep just fine. On 08/18/2010 08:56 AM, wd8chl wrote: On 8/17/2010 11:55 PM, Ray Brown wrote: > What do you do when you want to install a small UHF linking repeater on > a 4-story building that has no lightning protection on its' roof? (this is to > link an ambulance at a hospital to its' base repeater 40 miles away) > > From what I've heard, it may not be a good idea to hook it to the HVAC, > either. > > (sigh) > > > Ray, KB0STN No. I would find the nearest copper pipe from either the in-house water system or the sprinkler system, and clamp to that (making sure you don't crimp the pipe!!!) using #6 or maybe #8 wire if it's REALLY close (less then 5') Again, not as good as a dedicated system, but MUCH better then nothing.
