Advise on antenna lightning protection
Being a new ham, I am in process of setting up my first antenna. I decided on an openstub J-pole which will be installed about 9ft above my wooden deck. House and surrounding trees a higher than the top of the antenna.
As far as my research goes, the J-pole does not need grounding for proper operation but I still need protection from lightning storms which are frequent around here during summer.
My original thought was to put a 8ft copper rod into the ground and connect the antenna/mast as well as the coax lightning protector to the rod.
Then I started to do some research on the web, reading the IEEE guide for Surge Protection of Equipment as well as NEC requirements and several articles and comments in different fora.
Based on my newly acquired knowledge I looked at existing protection for satellite antenna, air conditioner etc.
Now I completely confused and I hope to get some guidance here.
According to NEC the house should have a central ground point to which all lightning currents will be conveyed.
Looking at the outside of the house, there is a metal pipe going into the ground right where the AC meter is located. About 1 foot from the pipe is a copper rod in the ground (no idea how deep) where phone and cable is connected to. In the basement I have the cold water pipe coming out of the ground an a (it seems) aluminum wire is clamped to it and disappears in the floor somewhere. The satellite disk as well as the satellite coax is 'grounded' on an outside PVC water pipe.
Here my questions:
1) Should I be concerned about the described situation?
2) Is in advisable to connect the antenna/mast/coax to the same copper rod than phone/cable? Even though it is probably 50' between rod and antenna?
3) Are you aware of any good guides on this topic on the internet.
Appreciate any comments
Well, it depends...
You generally don't want to make the mast part of your antenna, so grounding your coax at that end only works (properly) for some installations.
That said, yes, you do want only a common earth ground point for your house. Having more than one is dangerous if you have an insulation fault on different circuits, or a lightning strike nearby as induced voltages will differe between the circuits and bad things can happen from that.
Check out www.polyphaser.com. They have some very good references on how to properly ground a radio station (but you still have to consider your own situation).
As an example, I'm running a 5BTV vertical with about 100' of coax leading to it. Outside my window where the coax passes through, the lightning arrestors are installed (a Polyphaser IS-B50 and some other commercial arrestor - I forget the name). A #6 copper ground wire goes from the ground lugs on the lighting arrestors to a row of four 8' ground rods which are then bonded with #6 copper wire to the single earth ground point for the house's load center and telco connection. In this way, it's not possible to have an insulation fault or lightning groundstrike induce a high voltage across the shack wires into the house electrical wiring.
Polyphaser will tell you, all bets are off for a direct antenna strike, because lightning will go where lightning will go... However, a properly installed suppressor will minimize the surge that hits your equipment or the coax switch (if you turn off the antennas during a storm).
Also, the IS-B50 should not be installed near the antenna because it needs time for the strike impulse to travel down the coax and create a voltage differential it can then react to. If it's too near the strike, both the center conductor and shield will have the same voltage and little or no suppression will occur.
One last thing: Although a single copper-plated ground rod may suffice for the house earth ground, you will likely get far better earth ground performance from pounding in 1 or more (I'd say 3+ ) additional 8' ground rods and bonding them in a daisy-chain to your current ground rod. It's a fair amount of effort to pound those in with a sledge. Spacing is semi-important as well, There are several threads on this subject you can search for.
GL and 73, Dave
Last edited by KI6NNO; 06-27-2008 at 08:44 PM.
Reason: pretty much always miss something semi-important...
In general, EACH mast or tower should have a ground conductor going to it's own ground rod(s) first, THEN those grounds bonded to the other grounds at your place (Power, Telco, etc) #6 bare copper wire is the minimum size to use.
Flat copper strap (Roof flashing) Sold at most all home supply stores is much better to use for grounding your station "Single Point Ground"
For some good info:
Thanks for the replies, that helped a lot. And off I go to do some more reading about that
The more you read, the more confused it becomes.
At least in regard to the less than perfect solutions we do in our home stations.
QST had a nice two part article, and there are several good posting here in the QRZ archives. I too have read the Polyphaser book, the Electrical code, and about 100 posts on the subject.
ONE little piece of advice, which, if you REALLY do things well, you can ignore, but, since you will likely NOT do things that well, FOLLOW the advice....Disconnect your antenna when not using the rig.
One poster here said that was like leaving an unatended hand grenade, but MOST rational people will just say it is just a simple way of removing the most obvious danger, burning out the rig by a NEAR strike that induces current in your antenna.
A DIRECT strike, which seems to be VERY rare overall, is difficult to protect from UNLESS you follow a LOT of precautions, and follow them CORRECTLY and completely. I never have, most hams never do.
We just take whatever we feel is common sense for US, and try our best.
I have had about 4 NEAR strikes in the last 40 years, a rotor went, a burn mark on top of a rig, a fryed capacitor on a hard to get to antenna, and a chared piece of plastic on a large antenna knife switch. No destroyed radios, no blown computers, no fires, no melted coax, just one rotor indicator resistor.
The yard guy who cuts my lawn accidently hit the ground rod (now protected) for my main tower. ( There are NOW two ground wires and rods on each tower) and THREE on the one next to the house). When he loosend up the connector, I KNEW I should re-tighten it, I didn't, we had a storm that day, and I THINK that may have contributed to the problem.
In ANY case, I now also have Cinch-Jones connectors on each rotor control box, and keep those ALSO disconnected when not in use.
Again, I am just doing what seems to make sense for me, YOU may find another approach, but, lightning (a direct strike) seems to avoid hams for the most part....
One reason I suspect that is true, is that we tend to put a LOT of crap (er, antennas) on our towers, and THAT tends to dissipate the building up of the 'streamer' charge that induces a strike......
ANYWAY, best of luck with the new antenna set up.
Last edited by WA9CWX; 06-29-2008 at 09:36 PM.
"Clear intent is the best predictor of experience"
As for disconnecting the antenna when not in use:
Would it make sense to use a coax switch that, when an antenna is not chosen, it is connected to a ground? And it has a position that puts the rig to NO antenna, thus grounding all antennas and separating the rig? Does such a switch, designed specifically to work that way, exist? Or would a strike just pulverize such a switch and make the whole thing pointless?
Originally Posted by KA3JLW
Nearly all of the damage problem is ground loops through shields, or parallel currents on the center and shield.
Very little if any of the problem is a center conductor to shield differential unless you have a very special setup.
This is why if you talk to old timers who worked in BC and two-way long before the fancy lightning suppressors came around you will find everyone who had good cable routing and grounding had very few problems with lightning long before suppression devices were sold.
Now think about what the switch will do. It won't interrupt the primary path at all. So while it will offer some help for the less problematic differential mode problems, it won't change much in the way of primary problems.
If you do all the grounds properly outside and use an entrance plate that grounds the coax, and 99% of doing that properly is bonding things to the mains ground properly, then your best bet is to disconnect the coax and unplug the rig when not using it.
A grounding switch will certainly offer a small margin of additional improvement, but the only thing that really is worthwhile is pulling the plug and disconnecting the cable.
I never pull the plugs here unless I'm going away for a week. I never disconnect the feed cables. I don't have lightning protection devices and I have three towers that are over 200 feet tall, one is over 300 feet and gets hit almost every big storm. I never have problems.
The key is all in the cable entrances and the grounding, although the extra security of disconnects certainly is helpful in some cases.
I can't think of any antenna that should have an RF hot shield once the coax leaves the feedline connection to the antenna.
Originally Posted by KI6NNO
I can think of some antennas that are poorly designed that should NOT have a hot shield but do.
What type of antenna, other than a poorly designed one or a broken antenna, has voltage from the shield to ground?