Safety ground versus RF ground for a 2nd Floor shack
I know this has been addressed on the group before but I remain confused.
I will string a dipole in the trees. The coax shield will be earth grounded, as well as the balun and lightening arrestor. Now, in the 2nd floor shack, I've read that running a ground line from equipment 15 feet or more (in this case) to an earth ground will bring RF into the shack and be a potent source for TVI, etc. My choice, then, is to use the ground on the mains. Given that the shield is earth grounded on the antenna and the equipment is grounded to the mains, isn't this a good scenario for ground loop? Seems like a catch-22. My own gut says safety first, lower risk of RF issues after-the-fact by ? what ? I remember suggestions of coiling the ground wire in an RF choke, multiple ground lines of various lenghts to mess with harmonics. Ferrite beads? Chicken blood and a black cat? John |
Safety ground versus RF ground for a 2nd Floor shack
On Thu, 09 Mar 2006 23:28:12 -0500, jawod wrote:
I know this has been addressed on the group before but I remain confused. I will string a dipole in the trees. The coax shield will be earth grounded, as well as the balun and lightening arrestor. The BalUn? As for each, or the rest, where will that ground be? Back in the shack? Out below the antenna? Now, in the 2nd floor shack, I've read that running a ground line from equipment 15 feet or more (in this case) to an earth ground will bring RF into the shack and be a potent source for TVI, etc. Poor choice of reading. It should have been extensive enough to resolve your confusion. My choice, then, is to use the ground on the mains. Not always the best choice, but all such considerations have issues. Given that the shield is earth grounded on the antenna and the equipment is grounded to the mains, isn't this a good scenario for ground loop? You better believe it. Seems like a catch-22. My own gut says safety first, lower risk of RF issues after-the-fact by ? what ? You first have to figure out what ground means. I remember suggestions of coiling the ground wire in an RF choke, multiple ground lines of various lenghts to mess with harmonics. Ferrite beads? Chicken blood and a black cat? Hi John, A dipole certainly doesn't need a ground connection. Neither does a choke or BalUn. The lightning arrestor - obviously. But you are not going to do that through house wiring.... are you? No. So where? Starting with that last point, the ground needs to be close by the arrestor, and given the coax can be laid out anywhere, it may as well pass nearby your service ground where you can provide a short ground lead to the arrestor. Then follows the possibility of the ground loop. This will only arise if the safety ground carries current (it shouldn't) or the neutral return to that service ground does, and has some resistance to boot. It stands to reason there will be current, what remains to be seen is if there is appreciable resistance (a poor connection). Try as you might to avoid it, you WILL have a ground connection to the service ground from your rig (unless you are floating free on battery power and have absolutely no other accessories going to your rig). When you connect your arrestor to ground, this will guarantee a loop configuration. Any potential (pun intended) problem is strictly a matter of this resistance and current. I'll cut it short with this as questions are sure to follow. 73's Richard Clark, KB7QHC |
Safety ground versus RF ground for a 2nd Floor shack
jawod wrote: I know this has been addressed on the group before but I remain confused. My own gut says safety first, lower risk of RF issues after-the-fact by ? what ? I remember suggestions of coiling the ground wire in an RF choke, multiple ground lines of various lenghts to mess with harmonics. Ferrite beads? Chicken blood and a black cat? John, You have been misled and confused by bad information. Richard Clark has given you good advice. The only antenna that requires an RF ground is an antenna with a single conductor feedline worked against ground, or an antenna that is poorly designed or constructed. The only reasons to have a hamshack ground, unless you are trying to band-aid an antenna that is improperly constructed or feed a longwire, are electrical safety and lightning. Electrical safety can be taken care of by using a three wire outlet with grounding to the sagfety ground, and by following national codes. National codes require your station ground be bonded to the power mains entrance ground. We are not suposed to have two isolated grounds according to NEC, and it is a bad idea to have isolated grounds for lightning, safety, and RFI reasons. I'm afraid all the talk about ground loops and such have confused you. Try reading this: http://www.w8ji.com/ground_systems.htm 73 Tom |
Safety ground versus RF ground for a 2nd Floor shack
jawod wrote:
I know this has been addressed on the group before but I remain confused. I will string a dipole in the trees. The coax shield will be earth grounded, as well as the balun and lightening arrestor. Now, in the 2nd floor shack, I've read that running a ground line from equipment 15 feet or more (in this case) to an earth ground will bring RF into the shack and be a potent source for TVI, etc. My choice, then, is to use the ground on the mains. Given that the shield is earth grounded on the antenna and the equipment is grounded to the mains, isn't this a good scenario for ground loop? Seems like a catch-22. My own gut says safety first, lower risk of RF issues after-the-fact by ? what ? I remember suggestions of coiling the ground wire in an RF choke, multiple ground lines of various lenghts to mess with harmonics. Ferrite beads? Chicken blood and a black cat? John Reading the two responses so far...I'll get my advice elsewhere. Typical internet group response...mildly insulting and of no direct value. I first have to know what ground means? Whatever. Imaginary numbers apparently require imaginary minds. |
Safety ground versus RF ground for a 2nd Floor shack
jawod wrote:
I know this has been addressed on the group before but I remain confused. I will string a dipole in the trees. The coax shield will be earth grounded, as well as the balun and lightening arrestor. Now, in the 2nd floor shack, I've read that running a ground line from equipment 15 feet or more (in this case) to an earth ground will bring RF into the shack and be a potent source for TVI, etc. My choice, then, is to use the ground on the mains. Given that the shield is earth grounded on the antenna and the equipment is grounded to the mains, isn't this a good scenario for ground loop? Seems like a catch-22. My own gut says safety first, lower risk of RF issues after-the-fact by ? what ? I remember suggestions of coiling the ground wire in an RF choke, multiple ground lines of various lenghts to mess with harmonics. Ferrite beads? Chicken blood and a black cat? John John, So you are taking a balanced aerial, a dipole, chuck it onto a balun and the feed it with a coax. Nothing wrong with that... There should not be any "involvement" by the coax in the functionality of that dipole. The grounding of the coax are for shielding purpose only and as such, you ground the coax at one of the terminations, in your case, the transceiver. Building regs normally demand that the house's mains ground should be connected to a ground rod somewhere, normally at a central point. Assuming that every level adds 2.5m, you are sitting 5 meter up. Even if you ground your rig with a separate connection to a ground rod, you'll still be electrically 5 meter away from ground ( at least ). You will always have RF in your shack PERIOD, It's just a question where it is and how you discover it. It's either RF current or RF Voltage. As the RF voltage is what you normally discovers by having a "hot" key or transceiver, you need to phase shift the ground connection of the coax in time so you have a max current at your rig instead of high voltage. This is solved by using an artificial ground. Buy or build one, they are dirt simple. MFJ sells one. The artificial ground is basically a capacitor and an inductor in series with the coax SHIELD(!). Both cap and coil is variable/tunable. By changing the cap and coil, you can move the RF Voltage and RF current +/- 90 degrees. You just adjust for max RF current at your operating frequency. This worked fine at the 32nd floor for me... Cheers Dan / M0DFI |
Safety ground versus RF ground for a 2nd Floor shack
One way to beat this is to tune with low power and touch the
rig. Every few days increase the power until you have built up a tolerance to the RF tingle. You could also try this with the household power, starting at 2 or three volts, and increasing it gradually over time until you build up your immunity to electric shock as well. Irv VE6BP :-) |
Safety ground versus RF ground for a 2nd Floor shack
There is absolutely no reason to have an RF ground unless:
1.) You are end feeding a single wire antenna that is brought into the shack 2.) The two conductor feedline you have brought in, be it coax or open wire, is connected to an antenna that is not properly designed or installed The safety ground is required. The RF ground is a band-aid for something else being wrong. 73 Tom |
Safety ground versus RF ground for a 2nd Floor shack
Irv Finkleman wrote:
One way to beat this is to tune with low power and touch the rig. Every few days increase the power until you have built up a tolerance to the RF tingle. You could also try this with the household power, starting at 2 or three volts, and increasing it gradually over time until you build up your immunity to electric shock as well. Irv VE6BP :-) I tried this approach several years ago...got up to about half a kilovolt... but my wife complained that my glow was keeping her up at night. |
Safety ground versus RF ground for a 2nd Floor shack
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Safety ground versus RF ground for a 2nd Floor shack
On Sun, 12 Mar 2006 22:39:51 -0500, jawod wrote:
If I run a low gauge wire from that earth ground to the main box ground, then this is prevents ground loop? What if the distance to the mains box is 60 feet? Hi John, This is required by code. Violate code and insurance can dump your policy faster than a lightning strike. The whole point of that wire is to prevent ground loops - this one being the mother of all loops. If and when lighting gets snubbed by your arrestor, it will bury that charge into this inferior ground (the non-code unconnected ground that is), lift that ground's potential, and that potential will follow its way into the shack (along the shield) to find your safety ground (which is far better suited for that path) and you might happen to be sitting on the shoulder of that current superhighway. The resistive earth path between your arrestor ground and service ground is not nearly as attractive as the path from safety ground, through power supply, through chassis, through transmission line shield to the arrestor. It is a rare power supply that breaks that path's DC continuity, and a rarer one that RF isolates it both. Unless you are running solely on battery, no charger, and no accessories connected to the rig - there is a path to ground that lightning will find as an alternative. 60 feet is trivial for safety (the RF in lighting is more LF or MF than HF). 73's Richard Clark, KB7QHC |
Safety ground versus RF ground for a 2nd Floor shack
jawod wrote: If we assume that there is a well matched antenna: twin line to balun, SWR does not cause ground currents or RFI. coax to transceiver. My RF concern was that a long line to ground would serve as an antenna to bring RF into shack. If this is not the case, or if this is easily dealt with, great. A long line to the ground definitely WILL act like an antenna, but the effect is absolutely unavoidable. If you look up national electrical codes you'll see external wires or cable grounds entering a dwelling are supposed to be bonded or grounded to the same ground as the power mains and other utilities. This is primarily to ensure if there is any type of ground fault or surge (i.e. lightning) everything in the house rises at the same rate. You don't want ANY surge current flowing through the house wiring, and bonding grounds outside the house greatly reduces currents through the house. This is called a "common point ground", and it REDUCES ground loops. Second, amateur gear is not normally UL/CSA approved. It sometimes contains high voltage. High voltage inside a metal box can be a problem. If you get a short from a transformer primary to secondary the case can actually rise to the full amount of high voltage. That voltage can appear on antenna cables (as it can if other components inside the box fail), or between that device and other devices. While not all amateur stations have HV devices, most have line operated equipment. It is possible to have 120VAC appear on cabinets and cables in those devices. Because of this, we should always have an independent safety electrical ground. That ground is required by code to be bonded to the service ground. That leaves us RF. There are only two things required for RF in the shack prevention. The first is you use an antenna with a two conductor feedline. It can be coax or twinlead. The antenna system can have ANY SWR, but it must ensure the currents on each conductor of the coax or twinlead are perfectly balanced and 180 degrees out of phase. http://www.w8ji.com/verticals_and_baluns.htm If the currents are not balanced, some current will flow back to the power lines, telephone lines, and other connections to the station equipment. The cure for this is really fixing the antenna system. Although a "RF ground" in the station can cover up the problem, the feedline will still radiate and receive signals. The second is your station must have a common "ground buss" and all equipment in your station should be bonded to that ground buss. The importance of an external low impedance RF ground on that ground buss is actually very minor. The real importance is that ALL equipment in the shack operate at the same RF potential. In second floor locations I actually laid aluminum foil under carpet for my shack RF ground, the large "plate" acting like a groundplane for RF, but I ALWAYS had an external safety ground. That's because I always ran amplifiers and other equipment that was not UL/CSA listed. Sometimes you just do what you have to do to get on the air. It's best if you work out any RF problems IF they occur. If it was me, I would not worry about RF problems until they showed. Safety is another issue. If you are dead or the house burns down, it is too late to work on problems. The mains box is on the opposite side of the house...that ground is not conveniently located. What you do is up to you. I'm only telling you what the NEC tells us we should do and why. It does NOT mean your insurance will be invalid if you don't follow NEC, it only means they can cancel you. State laws require insurance companies honor policies, but if they find out something isn't safe they can cancel you. Otherwise they can only refuse to pay for fraud or an intentional violation of the agreement you signed. You station is less safe for lightning and for electrical safety if you don't bond the grounds, but I have had many stations over my lifetime that did not follow that guideline. That's what you should do, and you should do it for electrical and lightning safety. My coax will go thru a lightening arrestor (Polyphase) which will be earth grounded. If I run a low gauge wire from that earth ground to the main box ground, then this is prevents ground loop? What if the distance to the mains box is 60 feet? Yes. It reduces chances of harmful ground loops. I believe you should find that on polyphasers site in technical papers. Try: http://www.polyphaser.com/ppc_TD1016.aspx and other technical papers. 73 Tom |
Safety ground versus RF ground for a 2nd Floor shack
jawod wrote:
Reading the two responses so far...I'll get my advice elsewhere. Typical internet group response...mildly insulting and of no direct value. I first have to know what ground means? Whatever. Imaginary numbers apparently require imaginary minds. Richard wrote a very detailed response which covered pretty much everything you need. Perhaps you did not read it all. What didn't you understand? If you didn't understand something, you should have asked about what you did not, and he would gladly (I'm assuming, but I'm pretty sure on this) have answered your question. tom K0TAR |
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