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Station With Center-Fed Dipole - Best Grounding Technique?
Okay, since I'm installing an entirely new setup, what I'm looking for
here is the best way to ground my equipment and a large center-fed wire dipole. Lets start with the shack first. The radio and speaker are both connected to the house ground through their power cords. To provide better RF grounding, I'm thinking of everything (including radio & speaker) connected with 1" copper braid to two salted (for increased conductivity) ground rods just outside. Is that sufficient? Next, to reduce the likelihood of lightning reaching the shack, the only thing I can think of is a lightning arrester inline to two additional salted ground rods, with the coax disconnected when not used. I don't believe RF is an issue with a dipole, so is this sufficient for lighting protection? Give me your opinions. Am I missing something? Is there a better way? stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
wrote in message ... Okay, since I'm installing an entirely new setup, what I'm looking for here is the best way to ground my equipment and a large center-fed wire dipole. Lets start with the shack first. The radio and speaker are both connected to the house ground through their power cords. To provide better RF grounding, I'm thinking of everything (including radio & speaker) connected with 1" copper braid to two salted (for increased conductivity) ground rods just outside. Is that sufficient? Those 2 rods must be connected directly to your house power service ground with (i think) #4 or larger wire. This is a serious safety issue. This connection can NOT be through the green wire in the shack, it must be to the rod/wire that comes into the house. Note also, this is NOT an 'RF ground'... There really is no such thing as an RF ground, ground rods are all about power line and lightning safety. Salting rods is really not necessary unless you are in exceptionally poor soil, and then its more the water you have to use to keep them moist that helps the most... even salt in dry soil can't help you. Next, to reduce the likelihood of lightning reaching the shack, the only thing I can think of is a lightning arrester inline to two additional salted ground rods, with the coax disconnected when not used. I don't believe RF is an issue with a dipole, so is this sufficient for lighting protection? again, don't put in separate rods, all rods must be hooked together and to the service entrance ground. if you have coax lightning arresters they should be tied to the same ground as everything else where they enter the shack. disconnecting the coax from the radio can't hurt, but may not help much either. |
Station With Center-Fed Dipole - Best Grounding Technique?
Stewart,
The advice Dave gave is good. There is no perfect grounding installation, every one is a compromise to some degree. So I will describe a "close to" optimum setup and yours will be a compromise, but try to make it the minimum compromise you can. There are three grounds to be aware of. Safety, RF, and lightning or surge. 1. You are already covered for safety with the green wire ground. 2. You don't ground your equipment for RF grounding. Only some antennas need one, such as a vertical. Your dipole does not. 3. Lightning and surge protection ground - There should be only one grounding POINT, and it has already been established. It is the ground the power company uses. Any other ground you establish has to be connected to that one, as Dave described. The objective of surge protection is to keep the fireball outside of your house!! If you don't allow surges into your house it really simplifies the job of equipment protection. All conductors that come into your house need to be protected with proper surge devices. That includes telephone, cable tv, your 220 volt power, and your dipole coax. Ideally you have a plate (some think it has to be copper, but it can be aluminum as well) mounted right at the ground rod and on it you have a telephone line protector, a cable tv protector, and your coax lightning arrestor. Polyphaser and others make such devices. But the most vital of all is one that goes on your power line. Why ? Because any of these conductors can bring a lightning surge into your house, but the one that is most likely is the power line. It is called a whole house protector and it usually is installed by an electrician at the circuit breaker panel. The telephone line probably has gas tubes protecting it. Cable TV will have a little block, hopefully tied in already but it doesn't have gas tubes in it so it can use help. In the way of compromises, usually you have to bring in the coax at some other point. If you do, you ground the coax shield with the lightning arrestor to a ground rod, but as Dave described that rod has to be tied to the power company ground. Etc. etc. If you had residual surges that you were concerned with, AFTER you did all the above, then the next step is to bond all of your equipment together and tie it to the ground point. As you now know, if your shack is not located next to the ground point mentioned above, you have to provide a good and short conductor to that point. Good luck. Rick K2XT |
Station With Center-Fed Dipole - Best Grounding Technique?
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Station With Center-Fed Dipole - Best Grounding Technique?
Thanks for the replies, Dave, Rick, and Jim. Since my ideas didn't go
over so well, perhaps it's best to just describe my setup and then listen to any suggestions. Since I'm not an electrical engineer, do try to keep things simple. As I said earlier, the radio and speaker are both connected to the house ground through their power cords. I've also installed an inverted V dipole in the back yard (the only place it will fit). The center (feedpoint) of the antenna is attached to the roof on the second floor (about twenty feet above the ground) and the two ends run out to the two corners of the backyard. That's the best I can accomplish given local antenna restrictions. My house is located on a hill with a top floor entrance and living area. Below that is another floor level with the backyard, with a basement below that. The radio will be located in the living room on the top floor, again one floor above the backyard. The coax (RG-8X) will run out a window on the second floor to the center (feedpoint) of the antenna attached to the roof just outside (a run of roughly 15-ft). Now, where (if any) should I add grounding to that setup? I was going to add a lightning arrester to the coax just before it enters the house (fed into two ground rods), but will forego that since none seem overly thrilled about the idea. By the way, a Yeasu technician once recommended salting ground rods to resolve a poor grounding situation at the time, so I've been doing that ever since (can't hurt), especially during the dry summer months. Adding water is pretty obvious, so didn't think I needed to spell that out, Dave. stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
noname wrote:
Thanks for the replies, Dave, Rick, and Jim. Since my ideas didn't go over so well, perhaps it's best to just describe my setup and then listen to any suggestions. Since I'm not an electrical engineer, do try to keep things simple. As I said earlier, the radio and speaker are both connected to the house ground through their power cords. I've also installed an inverted V dipole in the back yard (the only place it will fit). The center (feedpoint) of the antenna is attached to the roof on the second floor (about twenty feet above the ground) and the two ends run out to the two corners of the backyard. That's the best I can accomplish given local antenna restrictions. My house is located on a hill with a top floor entrance and living area. Below that is another floor level with the backyard, with a basement below that. The radio will be located in the living room on the top floor, again one floor above the backyard. The coax (RG-8X) will run out a window on the second floor to the center (feedpoint) of the antenna attached to the roof just outside (a run of roughly 15-ft). Now, where (if any) should I add grounding to that setup? I was going to add a lightning arrester to the coax just before it enters the house (fed into two ground rods), but will forego that since none seem overly thrilled about the idea. By the way, a Yeasu technician once recommended salting ground rods to resolve a poor grounding situation at the time, so I've been doing that ever since (can't hurt), especially during the dry summer months. Adding water is pretty obvious, so didn't think I needed to spell that out, Dave. stewart / w5net Do you have metal water pipes upstairs with continuity to a spot near the ground rods downstairs? If so you can run a strap to your shack upstairs, and another from the water pipe to the ground rods downstairs. You need an RF ground (as the safety ground is the 3 prong Edison.) MFJ makes an artificial ground. Do you use a balun at the antenna feedpoint? How do you tune the inverted-V? |
Station With Center-Fed Dipole - Best Grounding Technique?
d
Do you have metal water pipes upstairs with continuity to a spot near the ground rods downstairs? If so you can run a strap to your shack upstairs, and another from the water pipe to the ground rods downstairs. bad plan. 1) Water pipes may or may not have good electrical conductivity. 2) You're asking for leakage current to flow in the pipes: corrosion is one possibility, shocks to people touching the pipes or plumbing is another. 3) If you also have the third wire ground to chassis, good chance you've now created a big receiving loop consisting of the pipes and your house electrical systems. Not good. 4) Using plumbing systems for electrical safety bonding/grounding is not recommended in any of the recent editions of the electrical code, and is certainly not a good idea for RF currents. You need an RF ground (as the safety ground is the 3 prong Edison.) MFJ makes an artificial ground. If it's a coax fed antenna, there should be no need for any sort of RF ground in the shack. Do you use a balun at the antenna feedpoint? How do you tune the inverted-V? Good RF chokes on the coax at the feedpoint and at the point of entry would go a long way to eliminating any "RF in the shack" problems. A couple 2.4" 31 mix cores with half a dozen turns on them, for instance. Whether the V is tuned or not won't have any effect on RFI or grounding. |
Station With Center-Fed Dipole - Best Grounding Technique?
On Mon, 04 May 2009 13:14:04 +0200, noname wrote:
Now, where (if any) should I add grounding to that setup? I was going to add a lightning arrester to the coax just before it enters the house (fed into two ground rods), but will forego that since none seem overly thrilled about the idea. Hi Stewart, A very good description of your set-up. You are already grounded through a the haphazard path of your AC outlet - if you chose to use three prong connections, if your outlet is in fact grounded, if your equipment actually has a safety ground to chassis. A lot of "ifs," hence my use of "haphazard." By deliberately adding a ground wire going to an ad-hoc ground rod, you can easily introduce problems. The worst of which could be lethal, but that extreme is unlikely (except it might only be resolved at the coroner's inquest). Consult code for grounding requirements. The minor problems include ground loops that can plague your listening and/or your contacts asking what that strange music is in the background of your transmission. The loops can burn out wiring in your rig (actually, more like traces on cards). The oddities that arise from ad-hoc grounding scroll out on a list of complaints that many come here to find solution for. By the way, a Yeasu technician once recommended salting ground rods to resolve a poor grounding situation at the time, so I've been doing that ever since (can't hurt), especially during the dry summer months. Adding water is pretty obvious, so didn't think I needed to spell that out, Dave. That sounds like a fantasy. If this thread doesn't grow suitably to fill in the vacuum of information, you can do a search in google groups, for this group, using the key word GROUND and CODE. 73's Richard Clark, KB7QHC |
Station With Center-Fed Dipole - Best Grounding Technique?
Jim Lux wrote:
Do you use a balun at the antenna feedpoint? How do you tune the inverted-V? Good RF chokes on the coax at the feedpoint and at the point of entry would go a long way to eliminating any "RF in the shack" problems. A couple 2.4" 31 mix cores with half a dozen turns on them, for instance. Whether the V is tuned or not won't have any effect on RFI or grounding. A BalUn would help a lot. Since we are sticklers for the NEC, Homey needs a #6 wire from where the transmission line enters the dwelling to an 8' copper clad rod driven into the earth, as close as practicable. |
Station With Center-Fed Dipole - Best Grounding Technique?
In article ,
Richard Clark wrote: By the way, a Yeasu technician once recommended salting ground rods to resolve a poor grounding situation at the time, so I've been doing that ever since (can't hurt), especially during the dry summer months. Adding water is pretty obvious, so didn't think I needed to spell that out, Dave. That sounds like a fantasy. If this thread doesn't grow suitably to fill in the vacuum of information, you can do a search in google groups, for this group, using the key word GROUND and CODE. 73's Richard Clark, KB7QHC It really depends on the area that your trying to build the RF Ground on, or into. Here in Alaska much of the earth (Dirt) is just plain Silica Sand, and rock, with very little mineralite in it, and is about as effective an RF Ground as a piece of Glass. We use Dipoles a lot just for that reason as they don't required an RF Ground to work against to radiate effectively. In some areas where Marconi type Antennas are used, and one MUST have an effective RF Ground, we have used Chicken Wire panels laid flat out from the base to 1/4 Wave at the lowest Frequency of intended use, and then Salted the dirt to add to the effective conductance of the Ground plane untill the chicken wire Rusts to the point of leaving just the conductive material in the top of the dirt. The Commercial AutoTune Antenna Tuners really don't work well without an effective RF Ground to work against, as the Microcode that runs them, can't deal with the very non-stable RF Grounding Systems. There are a number of ways to get single-ended Autotuners to tune Balanced Dipole type Antennas, and those are used as well. Much of the work done in the commercial MF/HF Communications Antennas Systems here in Alaska, was pioneered by the Engineering Staffs of the old Northern Radio Company, and then continued by Stephens Engineering Associates. (SEA) Both outfits were leaders in Bush Communications here in Alaska, in their day. -- Bruce in alaska add path after fast to reply |
Station With Center-Fed Dipole - Best Grounding Technique?
"dave" wrote
A BalUn would help a lot. For what? If the antenna system is balanced (as are dipoles, inherently), I seriously doubt a balun would be good for anything. |
Station With Center-Fed Dipole - Best Grounding Technique?
Howard Lester wrote:
"dave" wrote A BalUn would help a lot. For what? If the antenna system is balanced (as are dipoles, inherently), I seriously doubt a balun would be good for anything. He's feeding it with coax, so it's not just a good idea, it's required. The antenna is balanced, the feedline is not. He stated the feedline is RG-8X. tom K0TAR |
Station With Center-Fed Dipole - Best Grounding Technique?
dave wrote:
Since we are sticklers for the NEC, Homey needs a #6 wire from where the transmission line enters the dwelling to an 8' copper clad rod driven into the earth, as close as practicable. What if it is 1/4WL long? -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
Station With Center-Fed Dipole - Best Grounding Technique?
Cecil Moore wrote:
What if it is 1/4WL long? Then not only will he not be worried about insurance problems and nearby lightening strikes, but he won't be bothered with interference complaints, and all those annoying "Donald Duck" voices and beeps on the radio, etc. :-) Geoff. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM |
Station With Center-Fed Dipole - Best Grounding Technique?
Cecil Moore wrote:
dave wrote: Since we are sticklers for the NEC, Homey needs a #6 wire from where the transmission line enters the dwelling to an 8' copper clad rod driven into the earth, as close as practicable. What if it is 1/4WL long? "as practible" leaves some wiggle room. Charts of lengths to avoid are available. |
Station With Center-Fed Dipole - Best Grounding Technique?
"Tom Ring" wrote
He's feeding it with coax, so it's not just a good idea, it's required. The antenna is balanced, the feedline is not. He stated the feedline is RG-8X. I know that, and just because it's balanced to unbalanced, it's not *required.* The antenna system can work just fine without one. In some cases, at least according to the late Lew McCoy, it can do more harm than good. If the antenna system is inherently unbalanced due to one leg being, say, in greater proximity to metal and other objects, then I would consider using some kind of balun or choke system. |
Station With Center-Fed Dipole - Best Grounding Technique?
On Mon, 04 May 2009, dave wrote:
Do you have metal water pipes upstairs with continuity to a spot near the ground rods downstairs? If so you can run a strap to your shack upstairs, and another from the water pipe to the ground rods downstairs. Nope, nothing anywhere near the radio. All the water pipes in the house are on the opposite side, fifty feet or more from the radio. The shortest path to any ground whatsoever is directly out the window and down to the soil roughly ten feet below. You need an RF ground (as the safety ground is the 3 prong Edison.) MFJ makes an artificial ground. Do you use a balun at the antenna feedpoint? How do you tune the inverted-V? Nothing is permanently installed at the moment, so it's a fairly clean slate. The antenna (Alpha Delta Model DX-EE 40-20-15-10 meter dipole) was pre-installed to drill the hooks needed to hold it up, but it's now a pile of wires on the living room floor. The antenna doesn't have a balun of any type. While the antenna was up, I used an MFJ-207 Antenna/SWR Analyzer to get some very quick readings just to make sure the antenna would work. stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
Howard Lester wrote:
"Tom Ring" wrote He's feeding it with coax, so it's not just a good idea, it's required. The antenna is balanced, the feedline is not. He stated the feedline is RG-8X. I know that, and just because it's balanced to unbalanced, it's not *required.* The antenna system can work just fine without one. In some cases, at least according to the late Lew McCoy, it can do more harm than good. If the antenna system is inherently unbalanced due to one leg being, say, in greater proximity to metal and other objects, then I would consider using some kind of balun or choke system. http://www.bunkerofdoom.com/lit/bal_...baltransys.pdf |
Station With Center-Fed Dipole - Best Grounding Technique?
On Mon, 04 May 2009, Jim Lux wrote:
Where are you located? The recommendation will vary substantially if you are in Southern California (almost no lightning) or Orlando Florida (Lightning capital of the US, for all intents and purposes). Heidelberg, located in central Germany. Lightning is not a huge problem here, but one can perhaps never be too safe in that regard. By the way, the soil here is just fine as well and certainly doesn't lack moisture. Thus, since so many are fosusing on it, I'm sorry the salt was even mentioned. It's not needed in any way. It's just something I've gotten into the habit of doing. Hmm. and that Yaesu technician has what training and experience in grounding systems for lightning protection (other than what's printed in the front of the manuals)? And did the salting improve anything? if so, what? adding grounding is almost always the wrong solution to operational problems (RFI, for instance), since the purpose of grounding systems is to deal with abnormal events (short circuits, transients, etc.) The salt did indeed help in that particular situation. At the time, I was living on a hillside in Bremerton Washington, with the immediate countryside mostly small rock incapable of holding water for any length of time. The situation was so bad, my radio (Yaesu FT-847) would often instantly shut off due to high SWR readings, in spite of my ground plane antenna being fully functional with several (at one point eight) ground rods installed. The only way to prevent that was to add water around the ground rods each day, which usually worked only until the next day. Since adding more ground rods did nothing (and watering my antenna each day was quickly getting tedious), I called Yaesu thinking the radio might be defective. The technician recommended salt after agreeing my ground rods should be sufficient for the task. I was skeptical, but did as he suggested. Dug a hole (about a foot deep) around each ground rod, drove the rods in a bit deaper, poured in a generous helping of rock salt, and then watered the area long enough for the salt to spread into the soil. Of course, the radio was fine immediately after adding the water, but the real test was the next day once the water drained away. The radio did operate just fine that next day, and the day after that. In fact, the rock salt added to the soil (more added every two to three months) resolved the problem entirely the remainder of my time at that location. stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
On Mon, 04 May 2009, Richard Clark wrote:
A very good description of your set-up. You are already grounded through a the haphazard path of your AC outlet - if you chose to use three prong connections, if your outlet is in fact grounded, if your equipment actually has a safety ground to chassis. A lot of "ifs," hence my use of "haphazard." Okay, I have checked each of those. The house was recently inspected ensure compliance with recent building code requirements, with the outlets and overall grounding system checked for proper wiring at that time. The house wiring exceeded current building requirements, which I was indeed happy to hear. The radio uses a three-prong cord (a requirement here), with the chassis apparently connected at several points to the ground of that. It appears the antenna shield side of the connector is also bolted directly to that chassis. By deliberately adding a ground wire going to an ad-hoc ground rod, you can easily introduce problems. (snip) So you recommend no additional grounding? stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
dave wrote:
Jim Lux wrote: Do you use a balun at the antenna feedpoint? How do you tune the inverted-V? Good RF chokes on the coax at the feedpoint and at the point of entry would go a long way to eliminating any "RF in the shack" problems. A couple 2.4" 31 mix cores with half a dozen turns on them, for instance. Whether the V is tuned or not won't have any effect on RFI or grounding. A BalUn would help a lot. Balun/choke.. tomato, tomato.. they're really all the same thing. Keep the RF off the outside of the coax. Since we are sticklers for the NEC, Homey needs a #6 wire from where the transmission line enters the dwelling to an 8' copper clad rod driven into the earth, as close as practicable. The communications system (be it CATV, net powered broadband, amateur, etc.) would need to be bonded to any of the usual things that form the grounding/bonding system,e.g, one could "ground" through the metal conduit. A ground rod is, of course, not recommended in the current codes as a made electrode, and in any case, the code doesn't necessarily require a specially installed ground for this purpose. If you DO install another ground, then it has to be bonded with AWG #6 copper (or bigger) (can't use the conduit) Telephone has different rules. Must have electrode/grounding means as close as practicible to point of entrance, and the ground wire has to be AWG14 or large, insulated, in as straight a line as possible. Metal structure supporting outdoor antenna systems have to be grounded with AWG10 or bigger copper, AWG8 aluminum, or AWG17 copperclad steel, straight line. (the size requirement is for mechanical strength, not conductivity, which is why the copperweld(r) can be smaller) So you have these weird situations where the phone protection block has to be connected with AWG14 insulated to a grounding electrode as close as practicible, but then, because of the "bonding of electrodes" rules, you have to connect that electrode to the "house ground" with nothing smaller than AWG6. CATV is even different.. grounding block for drop has to be grounded to an electrode close to block and an *insulated* AWG14 or bigger run to bond with the rest of the house's grounding system. This sort of thing is why most ham installations aren't "code compliant"... heck, you could go insane trying to wend your way through the thicket of rules for the NEC. And that doesn't even begin to get into the transient suppression guidelines and/or NFPA 780 lightning protection rules. |
Station With Center-Fed Dipole - Best Grounding Technique?
Howard Lester wrote:
"dave" wrote A BalUn would help a lot. For what? If the antenna system is balanced (as are dipoles, inherently), I seriously doubt a balun would be good for anything. Most every practical dipole installation has some imbalance in the installation (the trees are closer to one side than the other, etc.).. a choke to prevent RF current from flowing on the outside of the feedline will at least make the pattern more consistent with expectations. Might make the tuning less "twitchy" too (because you've decoupled the effect of things near the feedline). Certainly, a choke at the entrance to the shack is a great way to keep RF outside. |
Station With Center-Fed Dipole - Best Grounding Technique?
Cecil Moore wrote:
dave wrote: Since we are sticklers for the NEC, Homey needs a #6 wire from where the transmission line enters the dwelling to an 8' copper clad rod driven into the earth, as close as practicable. What if it is 1/4WL long? The NEC cares not one whit for RF performance. The NEC rules are designed to keep the house from burning down or people dying if something happens: like a power line falling on the antenna. I read a quoted statistic (for which I can't find the original source, so it might not be trustable) that electrocution is the leading cause of death in connection with antennas. |
Station With Center-Fed Dipole - Best Grounding Technique?
I was skeptical, but did as he suggested. Dug a hole (about a foot deep) around each ground rod, drove the rods in a bit deaper, poured in a generous helping of rock salt, and then watered the area long enough for the salt to spread into the soil. Of course, the radio was fine immediately after adding the water, but the real test was the next day once the water drained away. The radio did operate just fine that next day, and the day after that. In fact, the rock salt added to the soil (more added every two to three months) resolved the problem entirely the remainder of my time at that location. The professionals use something like bentonite or montmorillion clay (kitty litter) as a soil admixture. The stuff is like a sponge and holds the water real well (by surface tension) and is very ionic as well, so the conductivity is good. You have to be careful, because too much causes an expansive soil problem. |
Station With Center-Fed Dipole - Best Grounding Technique?
On Tue, 05 May 2009 17:10:16 +0200, noname wrote:
On Mon, 04 May 2009, Richard Clark wrote: A very good description of your set-up. You are already grounded through a the haphazard path of your AC outlet - if you chose to use three prong connections, if your outlet is in fact grounded, if your equipment actually has a safety ground to chassis. A lot of "ifs," hence my use of "haphazard." Okay, I have checked each of those. The house was recently inspected ensure compliance with recent building code requirements, with the outlets and overall grounding system checked for proper wiring at that time. The house wiring exceeded current building requirements, which I was indeed happy to hear. Hi Steve, So, in fact your three prong plugs find their way to the panel ground. Can YOU find that ground? The radio uses a three-prong cord (a requirement here), with the chassis apparently connected at several points to the ground of that. It appears the antenna shield side of the connector is also bolted directly to that chassis. So, by this explicit statement, your "balanced" antenna has been unbalanced at the rig (which only further enforces the unbalance by virtue of the coax connection). By deliberately adding a ground wire going to an ad-hoc ground rod, you can easily introduce problems. (snip) So you recommend no additional grounding? This is a loaded question because there are TWO grounds which discussion often gets mixed. They may both go to the same point of zero potential, but their paths are what distinguish them. The TWO grounds are safety ground and RF ground. Any wire that is significantly long at a wavelength of your operation, will qualify more as a radiator than it will as a ground wire. Consider you are sitting at your transmitter, it has a dedicated newly applied ground wire that runs the shortest distance to what you think of as ground. Maybe that is all of 10 feet. You are operating on 10M. Ground is a quarterwave away. That puts your equipment at the high potential end of a wire with zero potential at ground. How grounded does that sound? The solution there is to add an artificial ground tuner to move that potential away from you (this would be an attempt to "balance" the distribution so that your equipment sits at an artificially imposed neutral - ground of another mother). Thing is, as I said, you already have a ground connection. The safety ground is a necessity unless you are very practiced in the art of isolation. You can add another path, and, again, that path may be a different length to the one you already have. Given that situation, you may find one path now spilling current into the new one - as dependant upon the wavelength of operation and the physical path lengths. When this spilling from one path into the other occurs, strange things happen compared to if you hadn't added that new path. More's to be said, but that's enough for now. 73's Richard Clark, KB7QHC |
Station With Center-Fed Dipole - Best Grounding Technique?
Richard Clark wrote:
On Tue, 05 May 2009 17:10:16 +0200, noname wrote: On Mon, 04 May 2009, Richard Clark wrote: A very good description of your set-up. You are already grounded through a the haphazard path of your AC outlet - if you chose to use three prong connections, if your outlet is in fact grounded, if your equipment actually has a safety ground to chassis. A lot of "ifs," hence my use of "haphazard." Okay, I have checked each of those. The house was recently inspected ensure compliance with recent building code requirements, with the outlets and overall grounding system checked for proper wiring at that time. The house wiring exceeded current building requirements, which I was indeed happy to hear. Hi Steve, So, in fact your three prong plugs find their way to the panel ground. Can YOU find that ground? The radio uses a three-prong cord (a requirement here), with the chassis apparently connected at several points to the ground of that. It appears the antenna shield side of the connector is also bolted directly to that chassis. So, by this explicit statement, your "balanced" antenna has been unbalanced at the rig (which only further enforces the unbalance by virtue of the coax connection). By deliberately adding a ground wire going to an ad-hoc ground rod, you can easily introduce problems. (snip) So you recommend no additional grounding? This is a loaded question because there are TWO grounds which discussion often gets mixed. They may both go to the same point of zero potential, but their paths are what distinguish them. The TWO grounds are safety ground and RF ground. Any wire that is significantly long at a wavelength of your operation, will qualify more as a radiator than it will as a ground wire. Consider you are sitting at your transmitter, it has a dedicated newly applied ground wire that runs the shortest distance to what you think of as ground. Maybe that is all of 10 feet. You are operating on 10M. Ground is a quarterwave away. That puts your equipment at the high potential end of a wire with zero potential at ground. How grounded does that sound? Worse than that. You've basically made a big loop antenna: greenwire ground to panel, panel to ground rod, ground rod to rig. The solution there is to add an artificial ground tuner to move that potential away from you (this would be an attempt to "balance" the distribution so that your equipment sits at an artificially imposed neutral - ground of another mother). Or, easier.. put a choke around the feedline where it comes into the shack, so that there's no appreciable RF current through the chassis and green-wire ground. Thing is, as I said, you already have a ground connection. The safety ground is a necessity unless you are very practiced in the art of isolation. You can add another path, and, again, that path may be a different length to the one you already have. Given that situation, you may find one path now spilling current into the new one - as dependant upon the wavelength of operation and the physical path lengths. When this spilling from one path into the other occurs, strange things happen compared to if you hadn't added that new path. Exactly.. one DC/Line frequency path is all that's needed for safety. |
Station With Center-Fed Dipole - Best Grounding Technique?
Jim Lux wrote:
Howard Lester wrote: "dave" wrote A BalUn would help a lot. For what? If the antenna system is balanced (as are dipoles, inherently), I seriously doubt a balun would be good for anything. Most every practical dipole installation has some imbalance in the installation (the trees are closer to one side than the other, etc.).. a choke to prevent RF current from flowing on the outside of the feedline will at least make the pattern more consistent with expectations. Might make the tuning less "twitchy" too (because you've decoupled the effect of things near the feedline). Certainly, a choke at the entrance to the shack is a great way to keep RF outside. A choke wastes power. |
Station With Center-Fed Dipole - Best Grounding Technique?
Jim Lux wrote:
Howard Lester wrote: "dave" wrote A BalUn would help a lot. For what? If the antenna system is balanced (as are dipoles, inherently), I seriously doubt a balun would be good for anything. Most every practical dipole installation has some imbalance in the installation (the trees are closer to one side than the other, etc.).. a choke to prevent RF current from flowing on the outside of the feedline will at least make the pattern more consistent with expectations. Might make the tuning less "twitchy" too (because you've decoupled the effect of things near the feedline). Certainly, a choke at the entrance to the shack is a great way to keep RF outside. A choke wastes power. |
Station With Center-Fed Dipole - Best Grounding Technique?
dave wrote:
A choke wastes power. I certainly wish that the RF power that left my lip with an RF burn scar had been wasted by a choke. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
Station With Center-Fed Dipole - Best Grounding Technique?
dave wrote:
Jim Lux wrote: Certainly, a choke at the entrance to the shack is a great way to keep RF outside. A choke wastes power. A properly designed common mode choke does not waste power. Roy Lewallen, W7EL |
Station With Center-Fed Dipole - Best Grounding Technique?
dave wrote:
Jim Lux wrote: Howard Lester wrote: "dave" wrote A BalUn would help a lot. For what? If the antenna system is balanced (as are dipoles, inherently), I seriously doubt a balun would be good for anything. Most every practical dipole installation has some imbalance in the installation (the trees are closer to one side than the other, etc.).. a choke to prevent RF current from flowing on the outside of the feedline will at least make the pattern more consistent with expectations. Might make the tuning less "twitchy" too (because you've decoupled the effect of things near the feedline). Certainly, a choke at the entrance to the shack is a great way to keep RF outside. A choke wastes power. How might this happen? The choke's not in the desired RF path (i.e. the inside of the coax and the antenna itself) Putting an RF impedance of, say, 5K in series with the current on the OUTSIDE of the shield should effectively reduce the current to zero, so there's no power being dissipated in the choke. Yes, if you use a choke with too low an impedance, it might dissipate power. |
Station With Center-Fed Dipole - Best Grounding Technique?
Tom Ring wrote:
He's feeding it with coax, so it's not just a good idea, it's required. The antenna is balanced, the feedline is not. He stated the feedline is RG-8X. The assembly instructions for the antenna say... The antenna is "..designed to be used with 50 ohm coax cable. No balun is required for proper operation. If RF on the coax is a problem, simply wind a "choke balun" with the coax that's used for your feedline. Wind approx 8 turns, at about an 8 inch diameter and tape (with outdoor rated black electrical tape), like a donut, and place this "donut" near the feedpoint of the antenna. You should leave about 2 foot of your coax sticking out of this "donut" for connection to the antenna. Then attach the end of your coax to the antenna connector on the center insulator, with the coax connector that is already on your feed line." In other words, a scramble-winding choke near the antenna's feedpoint, which I'll add if RF becomes an issue. As stated in my first message ("don't believe RF is an issue with a dipole," which should probably read "major issue"), I'm much more concerned with safety and lightning protection. stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
Jim Lux wrote:
Or, easier.. put a choke around the feedline where it comes into the shack, so that there's no appreciable RF current through the chassis and green-wire ground. Okay, I'm adding a balun. Now the question is what and where. The assembly instructions for the antenna say... The antenna is "..designed to be used with 50 ohm coax cable. No balun is required for proper operation. If RF on the coax is a problem, simply wind a "choke balun" with the coax that's used for your feedline. Wind approx 8 turns, at about an 8 inch diameter and tape (with outdoor rated black electrical tape), like a donut, and place this "donut" near the feedpoint of the antenna. You should leave about 2 foot of your coax sticking out of this "donut" for connection to the antenna. Then attach the end of your coax to the antenna connector on the center insulator, with the coax connector that is already on your feed line." In other words, a scramble-winding choke near the antenna's feedpoint. The alternative is an MFJ-915 in-line balun with 50 ferrite core beads on coax (cheaper than I can buy the ferrites), which MFJ says should be installed closer to the radio (3 feet) as opposed to the antenna feedpoint at the other end of the coax as described above. Which of the two options is most sufficient for the task and which is the correct placement for this - or are they both right depending on the type? stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
On Wed, 06 May 2009 01:54:34 +0200, noname wrote:
Okay, I'm adding a balun. Now the question is what and where. The assembly instructions for the antenna say... Hi Stewart, The answer to that is driven by the perceived problem. In a nutshell, if you don't have a problem, you don't need the balun (or choke). Knowing that you have a problem is another matter; but if you don't know what the problem is (the perception), you wouldn't know if it got fixed either. 73's Richard Clark, KB7QHC |
Station With Center-Fed Dipole - Best Grounding Technique?
noname wrote:
Jim Lux wrote: Or, easier.. put a choke around the feedline where it comes into the shack, so that there's no appreciable RF current through the chassis and green-wire ground. Okay, I'm adding a balun. Now the question is what and where. The assembly instructions for the antenna say... The antenna is "..designed to be used with 50 ohm coax cable. No balun is required for proper operation. If RF on the coax is a problem, simply wind a "choke balun" with the coax that's used for your feedline. Wind approx 8 turns, at about an 8 inch diameter and tape (with outdoor rated black electrical tape), like a donut, and place this "donut" near the feedpoint of the antenna. You should leave about 2 foot of your coax sticking out of this "donut" for connection to the antenna. Then attach the end of your coax to the antenna connector on the center insulator, with the coax connector that is already on your feed line." In other words, a scramble-winding choke near the antenna's feedpoint. The alternative is an MFJ-915 in-line balun with 50 ferrite core beads on coax (cheaper than I can buy the ferrites), which MFJ says should be installed closer to the radio (3 feet) as opposed to the antenna feedpoint at the other end of the coax as described above. Which of the two options is most sufficient for the task and which is the correct placement for this - or are they both right depending on the type? Read Jim Brown's RFI-Ham.pdf referenced in an earlier post. "choke baluns" made by winding coax are pretty much single band devices. A better approach is a single 2.4" toroid of suitable mix (#31 is good), and put a dozen turns of your RG-8x on it. Put one at the feedpoint, put one where it comes in the shack. Buy some extra cores because they make good RF filters for things like power cords (and the hole is big enough that a standard IEC power connector will fit through them) The MFJ915 is fine, although I wasn't able to find any actual performance specifications or details of what mix they're using. (in a few minutes of casual googling).. MFJs is probably an incarnation of the "W2DU balun", so the data Jim measured is probably reasonable. (about 1500ohms peaking at 10MHz) I think you'll get better results (cheaper) with the single big toroid..5 turns gives you more impedance than the W2DU, and it goes up from there ( based on the measurements in K9YCs paper.. page 12). The toroids run about $5. Most of the gain is from using a better mix (31) |
Station With Center-Fed Dipole - Best Grounding Technique?
Richard Clark wrote:
Hi Steve, I assume you're talking to me since you replied to my message. My name is Stewart, not Steve. So, in fact your three prong plugs find their way to the panel ground. Can YOU find that ground? I don't understand your question. The radio chassis is grounded to the wall outlet. The overall house wiring was recently inspected, with the grounding checked at that time. It was a thorough inspection which also included a device plugged into most outlets to check the wiring. Given that, I don't really know what I'm supposed to find and why. So, by this explicit statement, your "balanced" antenna has been unbalanced at the rig (which only further enforces the unbalance by virtue of the coax connection). I guess so. Actually, I don't really know. The radio was manufactured with the chassis grounded to the wall outlet and the antenna was designed by it's manufacturer to work properly with 50 ohm coax feed connected (I would assume) to a radio like this. What impact that has on balanced versus unbalanced is beyond me, and the same is true for what exactly you want me to do about it. stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
Richard Clark wrote:
Hi Stewart, The answer to that is driven by the perceived problem. In a nutshell, if you don't have a problem, you don't need the balun (or choke). Knowing that you have a problem is another matter; but if you don't know what the problem is (the perception), you wouldn't know if it got fixed either. Wow, your messages get more cryptic as they go along. I thought the very first message made it clear I'm not trying to fix a specific problem, but instead trying to head off some of the more common problems associated with a setup like this. Again, this is an entirely a new setup which has not been installed yet. What I'm seeking here is some input on the best way to do that. I'm fairly familiar with the basics of dipole antennas, but hoping for some solid advice from those with a lot more experience than my own. stewart / w5net |
Station With Center-Fed Dipole - Best Grounding Technique?
On May 5, 7:26*pm, Jim Lux wrote:
noname wrote: Jim Lux wrote: Or, easier.. put a choke around the feedline where it comes into the shack, so that there's no appreciable RF current through the chassis and green-wire ground. Okay, I'm adding a balun. Now the question is what and where. The assembly instructions for the antenna say... * The antenna is "..designed to be used with * 50 ohm coax cable. No balun is required for * proper operation. * If RF on the coax is a problem, simply wind * a "choke balun" with the coax that's used for * your feedline. Wind approx 8 turns, at about * an 8 inch diameter and tape (with outdoor rated * black electrical tape), like a donut, and place * this "donut" near the feedpoint of the antenna. * You should leave about 2 foot of your coax * sticking out of this "donut" for connection to * the antenna. Then attach the end of your * coax to the antenna connector on the center * insulator, with the coax connector that is * already on your feed line." In other words, a scramble-winding choke near the antenna's feedpoint. The alternative is an MFJ-915 in-line balun with 50 ferrite core beads on coax (cheaper than I can buy the ferrites), which MFJ says should be installed closer to the radio (3 feet) as opposed to the antenna feedpoint at the other end of the coax as described above. Which of the two options is most sufficient for the task and which is the correct placement for this - or are they both right depending on the type? Read Jim Brown's RFI-Ham.pdf referenced in an earlier post. "choke baluns" made by winding coax are pretty much single band devices. A better approach is a single 2.4" toroid of suitable mix (#31 is good), and put a dozen turns of your RG-8x on it. * Put one at the feedpoint, put one where it comes in the shack. *Buy some extra cores because they make good RF filters for things like power cords (and the hole is big enough that a standard IEC power connector will fit through them) The MFJ915 is fine, although I wasn't able to find any actual performance specifications or details of what mix they're using. (in a few minutes of casual googling).. MFJs is probably an incarnation of the "W2DU balun", so the data Jim measured is probably reasonable. (about 1500ohms peaking at 10MHz) I think you'll get better results (cheaper) with the single big toroid..5 turns gives you more impedance than the W2DU, and it goes up from there ( based on the measurements in K9YCs paper.. page 12). The toroids run about $5. *Most of the gain is from using a better mix (31) What if you use a coax with two shields, one shield for chassis ground which is the coax connection and the outer shield for earth/ground? Yes, there could be a ground loop but the nearest ground to a strike/ antenna is probably the best protection |
Station With Center-Fed Dipole - Best Grounding Technique?
On Wed, 06 May 2009 02:55:54 +0200, noname wrote:
Richard Clark wrote: Hi Stewart, The answer to that is driven by the perceived problem. I'm not trying to fix a specific problem Then there's no reason to fix imagined ones. Again, this is an entirely a new setup which has not been installed yet. Grounding has been covered, but, likely as not, you will have more problems there than anything over the air. As for antennas, I've read the advice offered to you by MFJ. Belts and suspenders kind of stuff, but that is the level of advice you can expect until you discover something wrong. Do everything suggested, and then do it again at different places. [Cryptic as it seems, eventually this lesson will emerge from the reams of advice.] You ask to prevent problems and I have pointed out they are only problems if you think (or get burnt when) they are. A bajillion operators live lives of happy operation with none of those "solutions" in place. Fix their "problems" and likely as not, nothing will get noticeably better, could eliminate some former contacts, and only make them grumpy about engineers crimping their fun. 73's Richard Clark, KB7QHC |
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