Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Mar 19, 2012.
You know I've been asking myself this very question of late.
Next stage would be an XOR-cist.
But ground issues can lead to all kinds of weirdo effects. If the computer and the displays are connected to different outlets then you can get strange effects.
Also if you have wired LAN then you shall have an unshielded TP cable between outlet in the wall and the computer, especially if the cabling to the outlet is shielded and that it's grounded by the switch and that grounding is on a different path where you have different sub panels with different loads causing "backcurrent" through the ground wiring. This could be a problem when the ground and neutral is shared, which isn't unusual in older installations.
As for computer power supplies - they have a tendency to "leak" a little AC to the ground from the RFI filter that's on the grid side.
I have seen examples of outlet "upgrades" where a 2-prong have been changed to a 3-prong outlet and then the ground is either not connected at all or connected to the conduit pipe where it tries to assume that the conduit pipe is grounded, something that's very unreliable and if the electrical system is upgraded on the path to the subpanel and the conduits are replaced to plastic conduits then things would get "interesting".
Then you have the situation where the neutral is "hanging in the air". That could get really "interesting". Most modern power supplies in computers runs from 100 to 240 volts with at least 50 to 60 Hz, so the problem might not be readily obvious unless you measure the voltage in the outlet relative to a know good ground.
Weak wiring overall can also be a problem if you have a powerful computer - some computers together with displays can consume quite a bit of power, so it's worth it to measure the voltage when the computer is on and running under load with all surrounding devices.
A power supply in the computer that's too weak could also be a cause for trouble.
Many computer problems are hw/driver related though. It's not always the latest driver that's the right driver, and sometimes the latest drivers aren't provided by Microsoft.
Have fun trying to drive out the devils!
Are you sure about it not being relevant to ham family at all?
RFI is a common issue when there's one or more ham radio stations in a neighborhood. In the case of computer malfunction, it's not the fault of the ham (who's licensed to emit electromagnetic energy). Instead, it's the lack of filtering and shielding in the computer and/or its modem, or other associated hardware.
Have you tried (as a substitute for an earth ground) a counterpoise, such as a series of wires of various lengths, fanned out from your computer in as many directions as practical, and reaching to the far corners of your abode?
Thank you for the most excellent original post and follow up conversation. It has cleared up some confusion for me.
A few of the things I've learned from this thread:
6 AWG solid tinned copper is sufficient for lightning dissipation because of the brevity of the event. Solid has better thermal mass than stranded and doesn't have as many problems with corrosion.
Ground rods are useful for low frequency power and DC. But for lightning you really want radials/rings or a grid near the surface to dissipate the charge and reduce "step potential".
All grounding conductors should be bonded together (AC ground, structural metal, concrete, roofing) to reduce potential between parts of the overall system.
To eliminate lightning risk for a piece of equipment there should only be one path to the equipment. As soon as there are two paths there is a possibility for a voltage potential to pass through the equipment and cause damage.
Ideally you want all outside connections to enter the structure at one point. You can still obtain some of the benefits without the SPG but this is a compromise.
Briefly: I'm not a ham but the 70' aluminum freestanding radio tower I'm building for LTE cellular radio has many of the same issues to deal with. My antennas (2 parabolic grids for MIMO) still need to be pointed with a rotator. The radio will be mounted on the tower near the antenna and powered with "power over ethernet". Data signal to the rest of the residence will be electrically isolated with a run of fiber.
I have a few questions:
I didn't hear any mention of lightning rods ("air terminals") on the thread. Unfortunately my mast is a little undersized and the relatively delicate top parabolic grid antenna is currently the tallest point. Does it make sense to bond a lightning rod to the top of the mast to shunt the brunt of the charge? (Doesn't seem like it would hurt anything other than the wallet.)
Tower and mast are aluminum. But the lightning charge will flow through the rotator and thrust bearing. Is this sufficient? Or should I add a loop of stranded copper to bridge the mast to the tower body? Similarly, is the bolted aluminum sections sufficient to move the lightning charge to ground or should I supplement with a continuous copper wire to the base?
Exothermic welding doesn't seem like a good idea on the aluminum tubing. I've got beefy Harger grounding clamps for each leg and the leg anchors are steel embedded in 6' of concrete. Will this be sufficient for bonding?
I need to bond the tower to the residence's grounding system. Straightest path is through an attic to an auxiliary distribution panel. Should I use bare copper (6 AWG?), insulated copper, just bond to the nearest j-box, or should I bury a copper loop around the perimeter of the structure to the service entrance?
I currently plan about four 40' grounding radials going off in several directions. These will be buried about 6-12" and will be bonded to the ring around the base of the tower with exothermic welds. Tree roots and other obstructions limit my ability to add more radials. Will this be sufficient or should I more effort into the radials?
Thanks again for the excellent advice on this thread,
Correct, I made no mention of Air Terminals because that is a completely different subject matter and becomes a moot point if there is a Tower involved. The Tower or Mast is effectively an Air Terminal. Adding an Air Terminal is not going to buy you anything if I understand you correctly.
No you should not need a Shunt (or bridge as you called it), would not hurt anything, I just don't see much value in doing so IMO.
Other than Coax, Signal, and Power cables, do not run any extra copper cable for ground as it is pointless and would NOT do anything. To lightning and RF, a single wire is just a large resistor, and the Tower Impedance is much lower. All it would do is add weight, wind loading, and cost with no benefit unless you call a downed tower from wind or ice a benefit.
No you cannot Exothermic Weld aluminum. The clamps are the proper type for your application. Keep in mind your Tower concrete piers are excellent Ground Electrodes, better than any Ground Rod you can sink because concrete is very conductive with a massive surface area in direct contact with soil with a very large cross-sectional area.
With that said, search Flea Bay and the beast from the Amazon for a product from Sanchem Inc called NO-OX-ID A-SPECIAL electrical grease. This stuff is what utilities, Rail Road, Military, Marine, and Civil Engineering use. Use it on all electrical connections sparingly. When used as instructed makes a life-time connection. It is inexpensive and a small tube will last you a lifetime.
Loaded question here, not sure you will like my answer or questions. Why would you run Tower Grounds through your house? I was under the impression you have a Mast on top of your house? Clarify please.
I can only assume, perhaps incorrectly, now you are talking about using the tower as a Vertical Antenna? Or are you using the Tower to elevate say VHF or UHF antennas? Two completely different applications. This might be a case where you have misunderstood terms and usage. Example a "RADIAL" has a couple of different meaning depending on context. In fact causes hams a lot of confusion, and I mean a lot of confusion that defies science.
If this Tower is a Vertical Antenna for HF, then you would be talking about RF Radials which have little or anything to do with dirt or earth ground. Last thing you would want to do is bury them 6 to 12 inches deep as that would completely defeat their purpose and destroy the antenna with significant Ground Losses. RF Radials are a Counterpoise or the other half of a Dipole Antenna. Stop and think about that for a moment or two. Go on-line and look for RF Ground Radial kits for HF. Everyone of them use small insulated wire laying on the Grass. RF cannot penetrate soil, and if you buried the radials more than a few inches, you are going to suffer significant Ground Losses. RF radials using small insulated wire laying on top of grass offers no lightning or electrical protection of any kind. They are just Counterpoises.
Now a commercial or goberment operator uses their radials as both an RF Counterpoise and Earth Ground (lightning protection. Projects I have worked on use tinned, bare, solid conductors just covered with dirt. Two projects, goberment, a very shallow trenches were scratched out, just enough to sink conductor below the surface, and then flooded with drilling mud, aka bentonite clay slurry.
I get the impression you are using the tower for VHF, UHF or even higher frequencies and thus have no use for RF Radials. Nor would you need 40 of them. At a minimum, 1 radial for each Tower Leg, nor more than 3 per leg ran as deep and long as possible. Rods not required. When used this way are just part of the Ground Electrode System, and has nothing to do with RF. You cannot use dirt as a conductor even if you wanted too. Voltage we use are just way to low. You have to get up to the 10's of thousands of volts to use dirt as a conductor. Only utilities can use dirt as a conductor.
Hope that helps, good luck.
That helps very much, thanks!
My only concern is that the relatively delicate parabolic grid antenna will be at the very top of the tower. They're made of aluminum, but not sure they can take the brunt of a lightning strike unscathed. So I may go ahead and potentially over engineer for peace of mind. Good to know that a shunt or other wiring to ground is unnecessary.
I already had some some Noalox, but this NO-OX-ID is even more versatile. I'll order some.
No, 70' tower is adjacent to residence and unconnected physically. I would like to bond the tower ground to the residential ground but the straightest path is through the garage attic. A much more difficult path goes around the garage.
Your last impression is correct. I'm using standard cellular 0.6 - 2.7 Ghz frequency range. The radials are purely for lightning dissipation. My current plan is to install 4 (one for each leg plus an extra) which will extend out about 40 feet from tower base.
Again, thanks for all your help Dereck!