|
|
|
Hi, Maybe advisable to check your own house first, eg. computer controlled,
washing machine, dishwasher, stove, TV, video or dvd machine, or hot water system etc. But I reckon the worst thing are the bedside "touch" lamps. Good luck. "Rick " wrote in message ... I am trying to locate the source of power line noise in my neighborhood. I drove around with a 10 meter am receiver with a base loaded vertical on the car and found the noise source is hard to pinpoint. Possibly this is because the noise is being conducted along the power line? What is the best way to locate the source. I am assuming if I can tell the power company that I am certain of the pole (cracked insulator ?) that is causing the problem I stand a better chance of getting action. A related question - IF I was to find the pole where the noise originates is there any chance of being able to actually see arcing occurring? Rick K2XT |
"Wes Stewart" wrote in message
Not really. Any decent power company will have an expert whose job it is to find this stuff. Mine (a rural co-op) does not, although they have tried very hard on several occasions. About the time I got their guy sort of trained, he was injured and retired. Subsequently, they called in the guy from the local metropolitan company with his specially equipped van and he found the problems almost immediately. Wes: I have previously pointed out that few to none of the electric utilities have noise experts any longer. Since deregulation, none of them want to try to justify the cost to their stockholders, and the accountants are firmly in charge. Ask Riley Hollingsworth or Ed Hare if you are reluctant to take my word. I have worked as an independent in this field since well before deregulation, and have watched the demise of the "noise expert". There are still a number of them active as private consultants, and there is plenty of work out here to keep all of us busy, but if there is still one employed by a utility company, I would sure like to know his name and the name of the utility, because I can no longer identify one from my lists. Rick: See: http://www.arrl.org/tis/info/HTML/power_line_handbook/ on the ARRL web site for further guidance. -- Crazy George Remove N O and S P A M imbedded in return address |
On Sun, 21 Mar 2004 18:53:49 -0600, "Crazy George"
wrote: |"Wes Stewart" wrote in message | Not really. Any decent power company will have an expert whose job it | is to find this stuff. Mine (a rural co-op) does not, although they | have tried very hard on several occasions. About the time I got their | guy sort of trained, he was injured and retired. Subsequently, they | called in the guy from the local metropolitan company with his | specially equipped van and he found the problems almost immediately. | |Wes: | |I have previously pointed out that few to none of the electric utilities |have noise experts any longer. Since deregulation, none of them want to try |to justify the cost to their stockholders, and the accountants are firmly in |charge. Ask Riley Hollingsworth or Ed Hare if you are reluctant to take my |word. I have worked as an independent in this field since well before |deregulation, and have watched the demise of the "noise expert". There are |still a number of them active as private consultants, and there is plenty of |work out here to keep all of us busy, but if there is still one employed by |a utility company, I would sure like to know his name and the name of the |utility, because I can no longer identify one from my lists. It's been a couple of years but Tucson Electric Power was the one. | |Rick: | |See: | |http://www.arrl.org/tis/info/HTML/power_line_handbook/ | |on the ARRL web site for further guidance. |
Thanks to all you guys for responding. Good info.
Here's a quick update. I turned off the main breaker in my house and still have the noise. As you experts point out, it is tough to get a bearing on the noise with HF measurements. I tried on 20, 15, 10 with a 3 element yagi and got peaks and nulls in different directions. Also with a 5 element 6 meter beam. Advice on the ARRL site said to use VHF, so as a first cut I drove the neighborhood with my FT100 mobile rig, mode AM, and 2 meter 1/4 wave antenna. S meter is approximately S2 everywhere except near two poles where it goes up to S7. This is a rural area, heavily wooded, with houses set way back from the street. Along the street there are many transformers on the poles, with taps coming from the high voltage. Also there are these approximately 1 foot long fuses. I know, because when the squirrels get across my transformer that is the fuse that blows like a shotgun. So there are many places where a bad connection could occur. This morning I make my first call to the power company. I'm in central NJ. Stay tuned. And thanks again for the tremendous help and interest. Rick K2XT ps - I started this discussion on the antenna newsgroup because it seemed most appropriate. I hope it's ok if we keep it here. I don't crosspost. |
Walking around using an old RatShack portable short wave radio I was able
to track down an unusual noise source (an incessant clicking that was all over 40-160m. I was able to aim the portable antenna at various wires while walking around. This particular noise turned out to be someone's bad telephone. When the telephone was disconnected, this loud click-click-click disappeared. Seems like that bad telephone was somehow "transmitting" this noise back through the phone lines. Admittedly the noise from the power lines here are much more difficult to pin down and seems to change with the weather. It can be very annoying and discouraging. There is a high voltage transformer right here next to the house, which means those hv lines are coming right down my driveway. Designing an antenna which is not even close to parallel to these power lines has helped somewhat. I am hoping the new 160m full wave loop which will be further away is going to be a big improvement. I am just hoping that the ladder line feed to this loop will not also pick up the noise. If so I will have to change that feedline to coax which will be a compromise. Impoving my RF ground and making sure it was totally independent from the A.C. safety ground at the house main has helped also. My primary RF ground cable goes through a hole in the floor at the station and immediately to a copper pipe driven in under the house. This first run is shorter than 6'. This first copper pipe is then tied to several others at about 10' apart to make up for the fact that they are only driven 5' into the ground. Make sure your RF ground is independent of the house AC safety ground. I also use a constant voltage transformer and a good power conditioner because the AC here is a mess. -bill Rick wrote: Thanks to all you guys for responding. Good info. Here's a quick update. I turned off the main breaker in my house and still have the noise. As you experts point out, it is tough to get a bearing on the noise with HF measurements. I tried on 20, 15, 10 with a 3 element yagi and got peaks and nulls in different directions. Also with a 5 element 6 meter beam. Advice on the ARRL site said to use VHF, so as a first cut I drove the neighborhood with my FT100 mobile rig, mode AM, and 2 meter 1/4 wave antenna. S meter is approximately S2 everywhere except near two poles where it goes up to S7. This is a rural area, heavily wooded, with houses set way back from the street. Along the street there are many transformers on the poles, with taps coming from the high voltage. Also there are these approximately 1 foot long fuses. I know, because when the squirrels get across my transformer that is the fuse that blows like a shotgun. So there are many places where a bad connection could occur. This morning I make my first call to the power company. I'm in central NJ. Stay tuned. And thanks again for the tremendous help and interest. Rick K2XT ps - I started this discussion on the antenna newsgroup because it seemed most appropriate. I hope it's ok if we keep it here. I don't crosspost. |
zeno wrote:
Walking around using an old RatShack portable short wave... Impoving my RF ground and making sure it was totally independent from the A.C. safety ground at the house main has helped also. My primary RF ground cable goes through a hole in the floor at the station and immediately to a copper pipe driven in under the house. I did the same thing -- a 10 ft copper clad steel rod driven through a hole in the concrete of my basement floor. The floor is about 5 feet below ground level. I found out later that this was not a great idea because the floor shields the ground below from moisture -- measuring the ground rod to my waterpipe later showed a dc resistance of almost 50 ohms -- it would have made a better dummy load. I have since put 4 10 foot copper clad steel ground rods outside and bonded them together using silver solder. This works much better. A chum of mine, noting my problematic results, decided to go sideways through his basement concrete intothe back yard where the soil would be moist. The end result was partially flooding his basement after the first rain! He wasn't home at the time! I should note that the ground rods only provide the safety ground, however they serve as the base for a number of other ground wires spread around the yard in a sort of helter-skelter radial system. This provides a pretty good RF ground. Moral: The best intentions often have unintended consequences! Irv VE6BP -- -------------------------------------- Diagnosed Type II Diabetes March 5 2001 Beating it with diet and exercise! 297/215/210 (to be revised lower) 58"/43"(!)/44" (already lower too!) -------------------------------------- Visit my HomePage at http://members.shaw.ca/finkirv/ Visit my very special website at http://members.shaw.ca/finkirv4/ Visit my CFSRS/CFIOG ONLINE OLDTIMERS website at http://members.shaw.ca/finkirv5/ -------------------- Irv Finkleman, Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP Calgary, Alberta, Canada |
On Sat, 17 Apr 2004 16:47:04 GMT, zeno wrote:
Make sure your RF ground is independent of the house AC safety ground. I also use a constant voltage transformer and a good power conditioner because the AC here is a mess. Hi Bill, The combination of these two statements could kill you. If AC is a mess, and if you have your own independent ground, then there may come a day when you connect/disconnect a wire between them (and it is guaranteed to be there) that has enough potential to blow your fuse. Think about it. The most common method of connect/disconnect involves the use of both hands, one wire in each (think of holding onto shelled connectors), with a path across the heart - classic killer scenario. Having separate grounds is against code. Being against code it is also a loophole for insurance to deny a claim if misfortune comes of this misapplication. Having separate grounds is also bad engineering and bad noise control. In short, there is no good reason to do it when it needs to be done right. What you have the potential for are problems called "ground loops." Closing or breaking those loops is what brings those problems. There was a thread in the last week with excellent links to how to do it right. I don't have them at hand right now, but you should research or prod me for more. 73's Richard Clark, KB7QHC |
"zeno" wrote in message ... Walking around using an old RatShack portable short wave radio I was able to track down an unusual noise source (an incessant clicking that was all over 40-160m. I was able to aim the portable antenna at various wires while walking around. This particular noise turned out to be someone's bad telephone. When the telephone was disconnected, this loud click-click-click disappeared. Seems like that bad telephone was somehow "transmitting" this noise back through the phone lines. Admittedly the noise from the power lines here are much more difficult to pin down and seems to change with the weather. It can be very annoying and discouraging. There is a high voltage transformer right here next to the house, which means those hv lines are coming right down my driveway. Designing an antenna which is not even close to parallel to these power lines has helped somewhat. I am hoping the new 160m full wave loop which will be further away is going to be a big improvement. I am just hoping that the ladder line feed to this loop will not also pick up the noise. If so I will have to change that feedline to coax which will be a compromise. Impoving my RF ground and making sure it was totally independent from the A.C. safety ground at the house main has helped also. My primary RF ground cable goes through a hole in the floor at the station and immediately to a copper pipe driven in under the house. This first run is shorter than 6'. This first copper pipe is then tied to several others at about 10' apart to make up for the fact that they are only driven 5' into the ground. Make sure your RF ground is independent of the house AC safety ground. I also use a constant voltage transformer and a good power conditioner because the AC here is a mess. -bill Hi Bill, Isolating RF ground from AC ground may be a solution in your individual circumstance, but it is not recommended or safe under normal conditions. Single Point Common Ground means what it says and nothing is "isolated". That begs for problems not the least of which is ground loops. I do exactly the same thing under my shack WRT multiple RF ground rods as you have and a very short drop to them as well - that elminates the chance for 1/4 wave multiples in the ground sytem to raise the impedance drastically. But according to best available practices and electrical code everything (antenna ground rods, RF ground rods, and service-mains ground rod) are all tied together. Understand that this in no way contributes in any way to "noise" in the receivers, and it can reduce noise significantly. It also helps minimize lightning damage, at least according to all the codes, writings, and many experts in this group. 73's Jack Virginia Beach |
OK, I guess I have to do more thinking about this, even though my head is
already totally spinning from the fact that there seems to be blatant discrepancies between expert opinions out there. I am new to this ng and have much to learn. I am not sure who to believe at this point. The book says "one common ground", AC safety AND RF, all one thing. This seems to be what is being advised here as well. This seems to be consistent with building codes. That is the "law", the politically correct physics, and what one needs to say in print or be liable, etc. Then I turn around, and experienced hams are telling me the exact opposite, eg. not to tie the RF ground to the house AC safety ground. To tie the RF ground to the house safety ground rod means a much longer run and thus the potential problems of 1/4 wavelength resonance also mentioned here. By the way, I am using an older Kenwood TS530S (until I get some experience and decide to invest in a more current rig). Are current rigs now always with three pronged polarized/grounded plugs? My unit here has a two prong non-polarized ac plug, just like the old audio tube amps I still use for hi-fi. This whole "ground" thing and its history is quite mysterious, controversial, and confusing to say the least. In 1953 when I was first a novice, I used a bizarre little homemade transmitter with one 117N7 tube which only plugged into one side of the house current!!!! and then used an earth ground and antenna. I am, in retrospect, amazed I am here and alive to tell the story. Where is Tesla when we need him...... Just curious, if I were to take a light bulb and connect ONE terminal to the hot side of an ac house outlet and then connect the other terminal to a ground rod driven into the ground in the middle of a forest somewhere where trees fall without anyone there to hear them, will the light bulb light up? bill (feeling a bit ungrounded at the moment.....) Jack Painter wrote: "zeno" wrote in message ... Walking around using an old RatShack portable short wave radio I was able to track down an unusual noise source (an incessant clicking that was all over 40-160m. I was able to aim the portable antenna at various wires while walking around. This particular noise turned out to be someone's bad telephone. When the telephone was disconnected, this loud click-click-click disappeared. Seems like that bad telephone was somehow "transmitting" this noise back through the phone lines. Admittedly the noise from the power lines here are much more difficult to pin down and seems to change with the weather. It can be very annoying and discouraging. There is a high voltage transformer right here next to the house, which means those hv lines are coming right down my driveway. Designing an antenna which is not even close to parallel to these power lines has helped somewhat. I am hoping the new 160m full wave loop which will be further away is going to be a big improvement. I am just hoping that the ladder line feed to this loop will not also pick up the noise. If so I will have to change that feedline to coax which will be a compromise. Impoving my RF ground and making sure it was totally independent from the A.C. safety ground at the house main has helped also. My primary RF ground cable goes through a hole in the floor at the station and immediately to a copper pipe driven in under the house. This first run is shorter than 6'. This first copper pipe is then tied to several others at about 10' apart to make up for the fact that they are only driven 5' into the ground. Make sure your RF ground is independent of the house AC safety ground. I also use a constant voltage transformer and a good power conditioner because the AC here is a mess. -bill Hi Bill, Isolating RF ground from AC ground may be a solution in your individual circumstance, but it is not recommended or safe under normal conditions. Single Point Common Ground means what it says and nothing is "isolated". That begs for problems not the least of which is ground loops. I do exactly the same thing under my shack WRT multiple RF ground rods as you have and a very short drop to them as well - that elminates the chance for 1/4 wave multiples in the ground sytem to raise the impedance drastically. But according to best available practices and electrical code everything (antenna ground rods, RF ground rods, and service-mains ground rod) are all tied together. Understand that this in no way contributes in any way to "noise" in the receivers, and it can reduce noise significantly. It also helps minimize lightning damage, at least according to all the codes, writings, and many experts in this group. 73's Jack Virginia Beach |
On Sat, 17 Apr 2004 18:42:44 GMT, zeno wrote:
Hi Bill, By the points offered: Then I turn around, and experienced hams are telling me the exact opposite, eg. not to tie the RF ground to the house AC safety ground. Experienced Amateurs (as distinct from experienced Professionals). To tie the RF ground to the house safety ground rod means a much longer run and thus the potential problems of 1/4 wavelength resonance also mentioned here. The basic confusion that arises is in the distinction between RF and Mains ground. You can keep your RF ground rod (add some radials to it to actually make it RF ground) as long as you tie it to the Mains ground (usually in close proximity to the drop and meter). The distance between THESE two points is immaterial RF wise as your RF ground will insure little or no RF current travels to the Mains ground. In THIS sense, they are separate. If there is noise (RF) on the Mains, it may seek your RF ground through this connection, but as long as you are not sharing it (you are not using this lead to both connect your equipment AND connect the two grounds) then there will be no problem. You should have a lead from your equipment to the RF ground and THEN to the Mains ground (two paths, one conductor) in that order: MAINSGROUND-------------RFGROUND------------SHACK GOOD MAINSGROUND----------SHACK-----------RFGROUND BAD By the way, I am using an older Kenwood TS530S (until I get some experience and decide to invest in a more current rig). Are current rigs now always with three pronged polarized/grounded plugs? My unit here has a two prong non-polarized ac plug, just like the old audio tube amps I still use for hi-fi. Most rigs aren't AC powered at all - they require 13.6VDC that comes from an AC powered DC supply. AC power is floating with a Hot/Neutral. Neutral eventually finds ground but you are in jeopardy of relying on that. Ground, the third wire, is a safety consideration and is never expected to conduct current except as a consequence of failure. Modern construction practices and code certainly mandates a thick enough conductor, but not for the purpose of supporting power needs. In 1953 when I was first a novice, I used a bizarre little homemade transmitter with one 117N7 tube which only plugged into one side of the house current!!!! This is also from an era when newspapers reported the passing of husbands or wives who, while washing the dishes, leaning on the stove, playing with the toaster, putting down the iron, turning off the mixer, or holding the refrigerator door.... leaned over to turn down the radio volume - classic across the heart scenario - classic results. They were killed by "modern" engineering design techniques to reduce noise (caps across the mains to the metal frame). Let's see, is it suppose to plug in this way, or was it the oth.*#!!**#..... 73's Richard Clark, KB7QHC |
I think this is starting to make sense, maybe. My RF ground rod which is directly
under the station about 6' directly down, also ties to a series of additional rods about 10 feet apart in both directions from that first rod (I am thinking this is like a radial since the bare wire connecting them is also on the earth (?). Should I connect the furthest rod of this series to the house mains ground rod which is actually not that far away at that point? Would I be ok then? -bill Richard Clark wrote: On Sat, 17 Apr 2004 18:42:44 GMT, zeno wrote: Hi Bill, By the points offered: Then I turn around, and experienced hams are telling me the exact opposite, eg. not to tie the RF ground to the house AC safety ground. Experienced Amateurs (as distinct from experienced Professionals). To tie the RF ground to the house safety ground rod means a much longer run and thus the potential problems of 1/4 wavelength resonance also mentioned here. The basic confusion that arises is in the distinction between RF and Mains ground. You can keep your RF ground rod (add some radials to it to actually make it RF ground) as long as you tie it to the Mains ground (usually in close proximity to the drop and meter). The distance between THESE two points is immaterial RF wise as your RF ground will insure little or no RF current travels to the Mains ground. In THIS sense, they are separate. If there is noise (RF) on the Mains, it may seek your RF ground through this connection, but as long as you are not sharing it (you are not using this lead to both connect your equipment AND connect the two grounds) then there will be no problem. You should have a lead from your equipment to the RF ground and THEN to the Mains ground (two paths, one conductor) in that order: MAINSGROUND-------------RFGROUND------------SHACK GOOD MAINSGROUND----------SHACK-----------RFGROUND BAD By the way, I am using an older Kenwood TS530S (until I get some experience and decide to invest in a more current rig). Are current rigs now always with three pronged polarized/grounded plugs? My unit here has a two prong non-polarized ac plug, just like the old audio tube amps I still use for hi-fi. Most rigs aren't AC powered at all - they require 13.6VDC that comes from an AC powered DC supply. AC power is floating with a Hot/Neutral. Neutral eventually finds ground but you are in jeopardy of relying on that. Ground, the third wire, is a safety consideration and is never expected to conduct current except as a consequence of failure. Modern construction practices and code certainly mandates a thick enough conductor, but not for the purpose of supporting power needs. In 1953 when I was first a novice, I used a bizarre little homemade transmitter with one 117N7 tube which only plugged into one side of the house current!!!! This is also from an era when newspapers reported the passing of husbands or wives who, while washing the dishes, leaning on the stove, playing with the toaster, putting down the iron, turning off the mixer, or holding the refrigerator door.... leaned over to turn down the radio volume - classic across the heart scenario - classic results. They were killed by "modern" engineering design techniques to reduce noise (caps across the mains to the metal frame). Let's see, is it suppose to plug in this way, or was it the oth.*#!!**#..... 73's Richard Clark, KB7QHC |
Richard Clark wrote: MAINSGROUND-------------RFGROUND------------SHACK GOOD MAINSGROUND----------SHACK-----------RFGROUND BAD I may still be confused here, not really fuly comprehending the above illustration. The mainsground comes to the shack anyway in the AC outlets powering the shack, being the third or ground terminal (although not really connecting to my Kenwood 530 which in this unique case only has a two prong AC plug and internal power suppy. I think this ground thing has to do with the "routing" as you indicate, just as the mystery of ground loops in an old tube hi-fi amp where the correct star grounding is the way to get rid of hum. As long as my shack RF ground is a short direct route to the first ground rod of the series, I should be ok then tying the mains ground to a "later" point in the RF ground rod system. (?) bill |
On Sat, 17 Apr 2004 20:15:21 GMT, zeno wrote:
I think this is starting to make sense, maybe. My RF ground rod which is directly under the station about 6' directly down, also ties to a series of additional rods about 10 feet apart in both directions from that first rod (I am thinking this is like a radial since the bare wire connecting them is also on the earth (?). Hi Bill, The additional ground rods don't do much, RF-wise. You are far better off with wire laid out radially on or just below the ground surface. However, what you have is good. Should I connect the furthest rod of this series to the house mains ground rod which is actually not that far away at that point? Would I be ok then? Depends on what you mean by furthest, but it sounds OK. Look at my answer in the other post. 73's Richard Clark, KB7QHC |
On Sat, 17 Apr 2004 20:22:56 GMT, zeno wrote:
Richard Clark wrote: MAINSGROUND-------------RFGROUND------------SHACK GOOD MAINSGROUND----------SHACK-----------RFGROUND BAD I may still be confused here, not really fuly comprehending the above illustration. The mainsground comes to the shack anyway in the AC outlets powering the shack, being the third or ground terminal (although not really connecting to my Kenwood 530 which in this unique case only has a two prong AC plug and internal power suppy. I think this ground thing has to do with the "routing" as you indicate, just as the mystery of ground loops in an old tube hi-fi amp where the correct star grounding is the way to get rid of hum. As long as my shack RF ground is a short direct route to the first ground rod of the series, I should be ok then tying the mains ground to a "later" point in the RF ground rod system. (?) Hi Bill, Look again at the illustration. Now think of noise originating in the Mains and traveling towards RF ground. That current, across impedance, produces noise voltage. In the "BAD" illustration, think of the left hand as hot, and the right side as cold. Just like at a setting of a potentiometer, noise voltage is injected INTO the SHACK if there are other paths to ground (there always are, you describe just exactly how it happens above). Now, repeat the same problematic noise current in the "GOOD" illustration. It sinks right into RFGROUND and does not proceed on towards the SHACK. You will of course have mixed grounds because this vale of tears we call reality demands that you power your SHACK from the Mains. And if it weren't that, it would be the 'puter, or the phone, or a battery charger for the drill (the list is endless and so common that we become blind to the obvious paths mixing noise into our life). Most local noise is conductive. That is, it comes from the source and the sink residing on the same breaker in the panel. The source noise current injects itself into the sensitive sink side that is sharing the path. By using an extension cord, you can confirm this by powering the noise source off another outlet that goes to a different breaker. That noise that is not conductive is radiative. It arrives from the source through the air. This can be nipped in the bud by using a transmission line choke at its entry (generally the feedpoint of the antenna). 73's Richard Clark, KB7QHC |
Most local noise is conductive. That is, it comes from the source and the sink residing on the same breaker in the panel. The source noise current injects itself into the sensitive sink side that is sharing the path. By using an extension cord, you can confirm this by powering the noise source off another outlet that goes to a different breaker. That noise that is not conductive is radiative. It arrives from the source through the air. This can be nipped in the bud by using a transmission line choke at its entry (generally the feedpoint of the antenna). 73's Richard Clark, KB7QHC Is this true for all antenna designs? Is this choke various depending on other characteristics of antenna and feedline. For example, in my anticipated 160m full wave loop which I plan to feed with diy ladder line to a Johnson Matchbox (250w), is there a specific recommendation for such a choke? Can I simply make what I need with a few windings of something around another round something and than wrapp it in rubber tape etc. Is this something I can incorporate into the hardware system at the antenna feedpoint where I will be attaching the two ends of my loop to the ladder line? -bill |
On Sun, 18 Apr 2004 02:48:58 GMT, zeno wrote:
Is this something I can incorporate into the hardware system at the antenna feedpoint where I will be attaching the two ends of my loop to the ladder line? Hi Bill, Feedline chokes are principally designed for the nature of coax which is unbalanced by design. Ladder line is presumably balanced and thus resists noise pickup of local origin. However, the balance is strictly a matter of its load, and if either end of the line meets an unbalance, the whole system is off balance and noise can intrude through what is called "the common mode." As such, balance is a very local thing that only you can determine through performance. I imagine that a loop would be harder to unbalance; but dipoles, especially low ones, are very susceptible. 73's Richard Clark, KB7QHC |
Richard Clark wrote: The additional ground rods don't do much, RF-wise. You are far better off with wire laid out radially on or just below the ground surface. However, what you have is good. How long should those radials be? and would just a couple be better than none? Bill |
Hi Richard,
OK, I will install the ladder line to the loop without embellishment first, then see how it performs in the specific locale then go from there. Bill Richard Clark wrote: On Sun, 18 Apr 2004 02:48:58 GMT, zeno wrote: Is this something I can incorporate into the hardware system at the antenna feedpoint where I will be attaching the two ends of my loop to the ladder line? Hi Bill, Feedline chokes are principally designed for the nature of coax which is unbalanced by design. Ladder line is presumably balanced and thus resists noise pickup of local origin. However, the balance is strictly a matter of its load, and if either end of the line meets an unbalance, the whole system is off balance and noise can intrude through what is called "the common mode." As such, balance is a very local thing that only you can determine through performance. I imagine that a loop would be harder to unbalance; but dipoles, especially low ones, are very susceptible. 73's Richard Clark, KB7QHC |
On Sun, 18 Apr 2004 17:48:23 GMT, zeno wrote:
Richard Clark wrote: The additional ground rods don't do much, RF-wise. You are far better off with wire laid out radially on or just below the ground surface. However, what you have is good. How long should those radials be? and would just a couple be better than none? Hi Bill, The current is densest at the feed point for a quarterwave vertical. Invest copper density in the first eighth wavelength with fewer radials migrating out beyond there, and so on for as much as you can tolerate. The classic FCC grounds run from 112 to 120 quarterwave lengths to give something like 95% shielding from ground (the point of radials). Scaling does not follow a strict law of proportionality as 60 would be 85% effective. The proportion is more log based than arithmetic such that a dozen (roughly a tenth of the FCC standard) would be at least 50% effective. Now, such pencil-whipping is based on abstractions drawn from full quarterwave radials under a full quarterwave radiator (classic field work for AM stations). As such, there are a lot of variables to consider, and yet a dozen, eighthwave long would be a solid RF ground. However, few of us have properties that long/wide (without things in the way) when trying to get into the 160M band game. So ultimately you do what you can and don't gloat to those who know better. On the flip side, 160M RF penetration into the ground is substantial and the traditional ground rods do offer some advantage, and as Reggie offers, so does the water service - find pipes. Another myth exploded is when you hear DXers crow about horizontals have no need of ground systems - they obviously have enough "gain" to discard the 1 or more dB advantage in a ground screen below their prima donna antenna. RF ground serves many functions: 1. A reference to tune against (stability, a sink - what you seek); 2. A shield to reduce ground loss (more gain); 3. A reflector to enhance low propagation angles (more gain). Please note that number 3 is offered for verticals only, at distances of many wavelengths away - such is the advantage of shore placed antennas. As such, "ground" is a misnomer (swamp, lake, ocean, or sea serves instead) - and ignore the babble about the "conductivity" of these being so much better. It is the drastic mismatch between the æther and the body of water that does the DX charm, conductivity is in the toilet. 73's Richard Clark, KB7QHC |
| All times are GMT +1. The time now is 01:37 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com