Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Yet more on grounding  (Read 1241 times)
EXWA2SWA
Member

Posts: 158




Ignore
« on: November 16, 2004, 12:36:35 PM »

I've done some reading on this topic here and elsewhere and am trying to get my thoughts together on this.

I don't think I'm looking for RF ground here so much as safety ground.

I've reconciled myself (but not yet my wife) to breaching the brick to carry ground outdoors to a ground rod. The plan is to use tinned braid between the various pieces of gear and a grounding buss made of 3/4" copper pipe. Then to use AWG4 wire from the buss through the wall to the rod. The run from buss to rod will of necessity be approx. 10'-12'. There's really no practical way to route wire underground to connect 2 or more rods more than a couple of feet apart.

Antennas will be attic-dwellers fed with coax from the shack to ladder-line on G5RV-Jr for HF and directly to an Arrow 146/440GP for VHF. Rigs are TS830S (standard old 2-prong AC line cord), ICOM 730 and Yaesu 2600M (both powered by a switching PS).

Wondering if it's advisable (or worthwhile) to:
(a) connect the buss to the 117AC socket ground (tying the two systems together)
(b) construct an antenna grounding buss with a couple of SO239's for Oklahoma's thunderstorm season. The idea would be to disconnect the antennas from the rigs/tuners and connect them to ground. The gear would be unplugged from AC and the transmitters put on 50-ohm dummy loads while the antennas were grounded.

Would welcome comments and suggestions, particularly the ones that say "Are you NUTS?"

Many thanks,
Jim
KE5CXX

Logged
KZ1X
Member

Posts: 3227




Ignore
« Reply #1 on: November 16, 2004, 12:47:32 PM »

If your antennas are inside the attic, why are you concerned about thunderstorms, or safety grounds?

If you are using a G5RV type antenna, how tall is your attic?  The feedline to that antenna *must* hang vertically, at least the balanced section up to the "balun" part.  (I have had zero luck using this antenna indoors, since my attics always had lots of AC wiring and HVAC ducts in them, and the G5RV has crazy reactances just by itself.  It cross-couples into anything within a 1/4 wave, so it seems anyway. YMMV.)

If you have balanced antennas (in other words, ones that contain both their 'driven' and 'image' elements) then you really don't need any "RF ground"
(whatever that is).

If you plan for an outdoor antenna, you will be rewarded for your investment in time and effort far greater than the payback from planning an unneeded grounding system.
Logged
K0IZ
Member

Posts: 737




Ignore
« Reply #2 on: November 16, 2004, 01:34:29 PM »

Change the power cord on the 830 to 3-prong so it will connect to the ground on your 120 volt circuit.  From safety perspective all of your equipment would then be grounded, just like other 3-wire devices plugged into power.  Like above post, not sure why the concern about lightning ground on an attic antenna.  If lighting is going to strike, it probably already has a bunch of stuff in the attic to hit.

With or without a ground, it is a good idea to disconnect antennas from rigs during storms.  Even without direct hit (unlikely), static buildup can damage components.
Logged
W4TME
Member

Posts: 299




Ignore
« Reply #3 on: November 16, 2004, 03:11:10 PM »

Jim,

I think what you are asking about is primarily a safety ground, but you may want to look at the RF ground as well since you are going to have antennas in the near field of you house AC wiring and will probably have some RFI issues as well.

Let’s look at you questions & comments.

"I've reconciled myself (but not yet my wife) to breaching the brick to carry ground outdoors to a ground rod. The plan is to use tinned braid between the various pieces of gear and a grounding buss made of 3/4" copper pipe. Then to use AWG4 wire from the buss through the wall to the rod. The run from buss to rod will of necessity be approx. 10'-12'. There's really no practical way to route wire underground to connect 2 or more rods more than a couple of feet apart."

Single point grounds are always good.  A copper pipe will make a good ground buss.  The AWG4 wire will provide an effective safety (AC) ground, but since it is high in impedance (small surface area), it will not make a good RF ground.  Because of your antenna system location (more on this later), I would consider also running some tinned braid of the same length as the wire as well to your ground rod. Also, the multiple ground rods out side do not need to be more that a few feet apart to be effective.  From my main ground rod, I have several other ground rods that are in a "hub-n-spoke" configuration that are no more than 4-6 feet away.  The more ground rod surface area you have in contact with the earth the better.  Put in as many as you can, particularly if the conductivity of you soil is poor.
 
"Antennas will be attic-dwellers fed with coax from the shack to ladder-line on G5RV-Jr for HF and directly to an Arrow 146/440GP for VHF."

Antennas in the attic will more than likely induce RF into your AC wiring and any other wiring that is near the radiating elements.  Having a good RF ground bonded to the house’s AC ground will provide that stray RF a low impedance path to ground.  You are probable going to need some ferrites and a choke balun on the HF stuff since the G5RV will have RF on the shield of the coax.  I have never run a G5RV, but those I know who do say it’s a touchy antenna and the proper geometry is paramount.  Good luck.

"Wondering if it's advisable (or worthwhile) to:
(a) connect the buss to the 117AC socket ground (tying the two systems together)
(b) construct an antenna grounding buss with a couple of SO239's for Oklahoma's thunderstorm season.
The idea would be to disconnect the antennas from the rigs/tuners and connect them to ground. The gear would be unplugged from AC and the transmitters put on 50-ohm dummy loads while the antennas were grounded."

I would not put a secondary connection from your ground buss to the AC wall socket.  Your connection with AWG4 is sufficient and will get grounded anyway if you follow the good advice from K0IZ that you need to change the power cord to three conductors and connect the ground to the chassis of the rig.  I would also recommend a good surge protector with a lot of RF suppression and isolation between NEMA connector banks, such as an Isobar Ultra series (http://www.tripplite.com/products/product.cfm?productID=104).  Also try to make sure that all of your A/C devices are plugged into the same circuit breaker so they are closer together in ground potential.

You probably are not going to have issues with direct strikes since the antennas are inside, but a grounding buss for the antennas isn't a bad idea.  More grounding is always better than less.  In addition, I would highly recommend lightning suppression from Polyphaser or ICE (my favorite) so that static and the electromagnetic pulses induced from near strikes will be shunted to ground rather than going to your rigs.  I live in central North Carolina and we can get lightning 12 months out of the year.  It can save your rig since induced EMP is a lot more probable than direct strikes.

-Tim W4TME
Logged
K6AER
Member

Posts: 3479




Ignore
« Reply #4 on: November 16, 2004, 03:21:26 PM »

I see common tread and what I would call an urban myth regarding indoor antennas and lightning. Just because an antenna is mounted indoors does not mean it is immune to a lightning strike. Thousand of homes are struck ever year from lightning and this is because the static cloud to earth discharge is looking for a ground path. The best ground path is the return ground in your home wiring and in some cases the antenna connected to you radio equipment. Treat all wiring and antennas inside or outside the same and provide AC surge protectors on your equipment and RF cable surge protectors on your antenna feeds. When you look at the insulating properties of a typical roof there is none compared to a billion volt discharge.
Logged
K1CJS
Member

Posts: 5871




Ignore
« Reply #5 on: November 16, 2004, 03:48:14 PM »

One thing you should NEVER do is connect your antenna directly to ground.  That will put ground potential up in the air at your antenna, attracting lightning--and you really don't want to attract it, do you?

If you want to destroy your antenna system, pull it down!  At least that way, you'll save your house!! ;-)
Logged
AA4PB
Member

Posts: 12673




Ignore
« Reply #6 on: November 16, 2004, 04:16:51 PM »

One thing you should NEVER do is connect your antenna directly to ground. That will put ground potential up in the air at your antenna, attracting lightning
-----------------------------------------------
Well, your antenna is connected to ground thru the radio and house wiring whether you like it or not. Even if the coax is left disconnected, it is not far from ground in comparison to the distance that the lightning has travelled before it got to your antenna. Now the real question is: would you like the lightning discharge to have a nice, low impedance path to ground thru a heavy guage wire and ground rod or would you rather that it travel thru your coax, radio, and house wiring on its way to ground? There is probably not one professional antenna installer in 1000 (if that) that would ever recommend NOT grounding your antenna to keep it from attracting lightning.

As for indoor antennas, they are probably no more likely to take a strike than the metal ductwork and the electrical wiring that is already in the attic.

Most lightning damage to radio equipment is not the result of a bolt of lightning directly striking the antenna (although that is possible). Most damage comes from currents induced into the antenna and feed lines from currents produced by lightning stiking other nearby objects (trees, etc).
Logged
K1CJS
Member

Posts: 5871




Ignore
« Reply #7 on: November 16, 2004, 04:57:27 PM »

Before you get your shorts afire there PB, read the gentleman's post.  The way it is written, it sounds like he wants to disconnect his co-ax from his rig and connect the center of it to ground.  Nobody said anything about not putting ground protection on the antenna, grounding it like that just makes sense.  But if the antenna is always connected to ground, how are you gonna get any worthwhile signal out of it, or for that manner, into it???

Ground protection on an antenna is good practice, inviting lightning to strike is not.  And grounding the center conductor, like it or not, IS inviting lightning to strike.
Logged
K1CJS
Member

Posts: 5871




Ignore
« Reply #8 on: November 16, 2004, 04:58:49 PM »

Oh, yes, I've always been told to disconnect the antenna connection form the rig and put it down away from ANYTHING electrical or conductive.  
Logged
AA4PB
Member

Posts: 12673




Ignore
« Reply #9 on: November 16, 2004, 05:54:07 PM »

Many antenna designs are DC grounded, even when they are in use. Many coax switches automatically ground the center conductor of an unused antenna. In my book it is a good idea to ground both the shield and the center conductor of an antenna when it is not in use. Grounding the center conductor is not going to "attact" lightning to the antenna.

Disconnecting the coax from the rig and leaving it lie on the floor or elsewhere around the shack is a bad idea in my opinion. If lightning energy does come down the coax it can jump feet to the nearest ground and that could cause a fire. You are much better off to have it grounded to a solid, low impedance ground so the current will have a good path rather than jumping across the room. If you are going to disconnect the coax then leave it outside as far away from the house as possible.
Logged
W4TME
Member

Posts: 299




Ignore
« Reply #10 on: November 16, 2004, 06:01:30 PM »

Think about it this way.  We are talking about a direct strike which is rare compared to the EMP produced by near strikes.  Your antenna, of which one part of it is ALREADY grounded on the coax shield (I am assuming that everyone follows the accepted practice of grounding the coax shield at the entrance of your home) is surrounded by other structures that are at the same relative potential, so grounding the center conductor  isn’t going to tip the balance and make your antenna “more negative” than the surrounding structures.  If it is a direct strike, a LOT of volts just traveled through tens of thousands of feet to hit your antenna.  Air is not a good conductor.  If your coax is disconnected lying on the floor or in a jar, all that potential is still looking for a path to ground.  Being disconnected it will take any random number of paths WITHIN your shack to find a low potential.  I would rather try to "suggest" a path to ground by having the center conductor grounded than not.  Then again, if it is a direct strike, you are still going to have a big mess on your hands.

-Tim W4TME
Logged
AE6RV
Member

Posts: 146




Ignore
« Reply #11 on: November 16, 2004, 07:29:33 PM »

If you get a direct strike to an attic antenna, chances are your house is on fire, and unless someone got hit by the incidental strike, you don't really care what happened as a result of the coax laying on the floor.

Bob
Logged
W3JJH
Member

Posts: 1422


WWW

Ignore
« Reply #12 on: November 16, 2004, 07:51:00 PM »

The National Electrical Code (Article 810 which covers Amateur Transmitting and Receiving Stations) REQUIRES that a bonding jumper no smaller than AWG 6 shall be connected between your station grounding electrode (the ground rod) and the building power grounding electrode (the mains power ground) [810-58 and 810-21].  Connecting to the third pin on an outlet is insufficent since its ground wire back to the service panel will be no larger than AWG 10 and can be as small as AWG 18.  BTW, 1-in flat braid is equivalent to AWG 7 and is does not meet this requirement either.  It is sufficient for the connections from the radios to the ground however.  In fact, AWG 14 meets the NEC requirement for an operating ground conductor between a radio and the ground rod [810-58(c)].  Of course, the flat braid will give better RF performance.

As for grounding your antennas, the NEC [810-57] REQUIRES that outodor antennas either be fed with coax with a "permanently and effectively" grounded shield or be fed with lightning arrestors on each lead wire or that the antenna itself be "permanently and effectively" grounded.  The purpose of the ground is protect the building from a lightning strike.  If you antenna is *inside* of the building, any lightning strike will hit the roof before it gets to the antenna and there's no practical protection from lightning in the grounding.
Logged
EXWA2SWA
Member

Posts: 158




Ignore
« Reply #13 on: November 17, 2004, 05:13:21 AM »

Some clarification on my part: it's not a direct strike that worries me, but the static charge & EMP that accompany near misses. I was headed for a 'fraidy-hole' a few years ago, carrying a portable radio with the line cord loose. Static electricity in the air jumped from that little lump of wire to the wet ground,  almost causing my wife to scream (she's not that excitable) and leaving me wishing I'd brought spare underwear.

Thanks to all who responded; I'll digest your suggestions and information and make better-informed decisions. I *knew* there would be some good reasons to ask "Are you NUTS?" and so appreciate your collective candor.


Logged
K8AC
Member

Posts: 1465




Ignore
« Reply #14 on: November 17, 2004, 05:19:37 AM »

I suggest that you carefully re-read W4TME's comments regarding induced currents from nearby strikes.  I'm certainly no expert on lightning protection, but have more experience than most since I suffered two direct hits within a year at my station.  In both cases, the strike hit my 160 meter inverted L.  With the first strike, I had the usual silly gas discharge arrestor on my coax where it entered the house.  It may even have fired - who knows.  I never paid attention to the recommendations for tying all the grounds together and having a common ground panel where the cables enter the house.  The equipment connected to my antenna coax didn't suffer any damage in the RF circuitry.  However, induced currents in my control lines for my outdoor relays resulted in very high potentials at the point where those wires connected to my gear.  Everything attached to my station power supply was damaged and my PC was destroyed since it was connected to the rig via RS-232C cables.  

After a lot of study, I implemented the suggestions found at the Polyphaser site as well as many ideas mentioned by W8JI.  In May of this year, an unexpected thunderstorm came up very quickly and the tree holding my 160 meter antenna was struck, with the antenna again becoming part of the ground path for the bolt.  This time, my outdoor relay boxes were zapped again, but the protection circuits on the relay lines in my grounding box apparently were effective.  This time, most of my damage came from currents induced in the underground telephone line.  Note that this line runs underground for at least 1 3/4 miles.  The line was melted open at the telephone box on the house and just about everything attached to the telephone line in the house was toast.  The induced surge travelled into the PC from the telephone line and from there to the station gear through the RS-232 lines.  All grounds, including telephone, power and station ground panel were correctly tied together.  While my satellite TV cable was also tied into my entry ground panel and had a Polyphaser arrestor on it, sufficient current was induced into the long run of cable inside the house walls to zap several units attached to that cable.

I believe that if I had connected everything to ground AT THE STATION DESK as well, and bypassed the control cables, etc. there with MOVs, I might have escaped damage this time.  

The net of all this: Don't spend all your time and money worrying about the effects of the direct strike.  The real damage may be done by induced currents, even on cables that are almost completely underground.  The fact that your antennas are in the house means nothing in avoiding damage from that source.  High potentials can reach your rig through telephone, cable TV, satellite TV or control lines for relays, rotors, etc.  If your station is a good distance inside the house from the common ground entry panel, a second common ground bus (connected to the first) is in order.  

Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!