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RFI: "Good RF Grounds" [Way too long!]
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
RF grounding and antenna concepts: Before opening this can of worms I want to explain the steps that lead to this thinking. The following is the result of a casual comment by William Fieldstone. I don't remember the exact question as it was in the middle of a frustrating antenna testing session. But several hours later I was thinking about his basic question and realized that in spite of being a SWL for over 40 years, a ham for over 25 years and an EE, I had never really bothered to think about the random wire antenna that many SWLs use. Perhaps because I started in radio way before I had any understanding and just had never bothered to reconcile the way I treated random antennas and what I knew to be the physics of how antennas operate. Either I can call it an epiphany or, as the new agers would say, a "paradigm shift". Or more likely I had simply been guilty of sloppy or muddled thinking. As I developed the thoughts that follow, I had many conversations with fellow hams, SWLs and some professional engineers that specialize in RF. Some of the conversations got very heated. I was spouting what was viewed as heresy. But after the dust settled everyone agreed with my conclusions. That doesn't mean I am correct, maybe my friends just gave in to my insane ravings to shut me up. I even went back to my college text books and reviewed the section of EM wave theory and antenna function. Before we discuss grounds we need a quick review of how antennas really work. Most of think that 'good RF ground' is a requirement. But stop and think a moment. A TV UHF antenna is a dipole. While we ground such antennas for safety reasons, a ground doesn't effect reception. Hams that operate in the HF, or SW, bands often use dipoles, beams, or loops. None of which need a ground to operate. It is true the ground near the antenna has a pronounced effect on many characteristics such as angle of radiation and to some degree the actual impedance and bandwidth. But a dipole would work just fine in free space. With the exception of 'Long Wire Antennas', Beverage and other surface or traveling wave antennas, all other forms of antennas are either loops or some form of dipoles. Loops and dipoles simply do not need a ground. Back in 1984 I was interested in low power, QRP, Ham HF operations. I used a simple home brew HF transmitter, direct conversion receiver and a dipole. I operated for several weekends from a friend's cabin in the Daniel Boone National Forrest and I used a dipole suspended between two convenient trees. I operated off my motorcycle battery and nothing was grounded. The battery was sitting on a wooden front porch picnic table. I worked 17 countries and 38 states in 3 weekends. While doing some R&D for a commercial WWV receiver installation I experimented with a dipole and a Panasonic RF2300. I was on the metal roof of a manufacturing plant, and I was not connected to ground in any way. And I had very good reception across the HF band with a dipole cut for 10.0MHz Will's question made me realize that with the exception of loops, all of the antennas I normally use are a dipole. In the case of the ever popular random wire antenna, the wire was clearly one element and the earth was the non obvious other half of the dipole. Take a look at any taxi, cop car, fire truck or even a car or truck with a CB. The vertical whip is part of the dipole and the car/truck body is the other part of the dipole. We call such antennas ground planes. A very effective 2M ham antenna can be made with a 19" vertical rod and a 40" diameter metal plate, or picnic table top. A 10 or 11 meter antenna can be created with a ~100" vertical whip and a ~200" metal roof. Both antennas do not need the 'ground plane' connected to the earth. Many hams use vertical antennas and all commercial MW stations in the US use vertical antennas. The FCC requires MW stations to use about 122 radials that form an effective ground plane. A few MW stations use an elevated set of radials that don't need to be grounded for proper operation. For lightning protection a ground is needed, but not for operation. Hams, and SWLs, that use verticals need to have enough radials to reduce the losses caused by poor soil conductivity. A 1/4 wavelength vertical element and an 8' NEC ground rod will be a very poor antenna. The all too common random wire antenna that is using the soil, a poor conductor unless you live in a salt marsh, is a very inefficient antenna. In extremely RF quiet locations such a setup works very well. My friend with the cabin deep in the Daniel Boone National Forrest lets my wife and me spend a week there every fall. There is no electricity, telephone, or cable TV service within a mile or so. In that location, a single random wire antenna, with no feed line, and using the well casing as a ground works VERY well. However at my home, such a setup is an absolute failure. The biggest problem with the all too common random wire antenna is the lack of isolation and the inherent high impedance and the extreme difficulty of achieving sufficient isolation from the noise within the home. So now we come to the main question: "What is a good RF ground?" It depends..... A better first question might "why do I need a good RF ground?" Remember that the earth is almost always an extremely poor conductor. Imagine trying to put up an antenna on a soil less rocky mountain top. Kind of hard to get any sort of ground. I have seen such a location that took a direct lightning strike. Given that lightning has traveled through several thousand feet of the world's best insulator, air, even the poor conductivity of rock looks like a very good ground. The surface of the rock was covered by what physicists call a dendrite pattern. Looked kind of like frost on a window. So why do we insist on trying to use such a poor conductor as part of our antenna system? Habit? Since SWLs typically listen from 100KHz to 30MHz, I am including LW and MW here, and since hams most often operate on a few narrow bands of frequencies the antenna we use are very often very dissimilar. A ham can get by with a couple of dipoles or even a single dipole with "traps" to add additional bands. SWLs can't do that. For a dipole the only ground that is needed is a safety ground. In a proper dipole there will be no ground currents. So if one is going to use a random wire antenna, we need to understand it is a poor compromise but it will work. By adding a 8' NEC ground rod at the feed line end, and by adding as many radials that are as long as feasible, we can boast both the performance of such an antenna, but more importantly we can achieve much higher attenuation of the noise from the home. Let's face it; on lower HF the background noise is high enough so that greater efficiency isn't that helpful. The improved unobvious leg of the dipole, the "ground", would have much better conductivity. But more important the conductivity for efficiency is the improved conductivity converts the pseudo dipole formed by the random wire antenna, into a more effective dipole. And this will allow a better match to the feed line. Better match equals increased isolation can lower the noise from within your home by at least 1 S-unit and many times by 3 or more S-Units. This is manna from heaven. If we decide to go with an active monopole antenna then the ground needs are very similar. Again a 8' NEC ground rod and as many radials as practical will create a "good RF ground. Of course we could forget the grounding rod and just go with a set of elevated radials, or in my case a metal roof and have very good reception. An active dipole doesn't need a ground for operation, although for safety and precipitation static an earth ground is very important. I am not a fan of loops, but if one decides a loop is the way to go, the RF ground really doesn't matter. The feed line does need to be bonded to the NEC required safety ground for lightning protection. In any case, the antenna ground ALWAYS needs to be bonded to the NEC safety ground. If you want to isolate the antenna ground then you need to use a broadband 1:1 RF transformer to achieve electrical isolation between the antenna/ground system and the house NEC ground. In a lightning strike that 1:1 will short and your antenna/ground will become some what connected to the NEC ground. In my experience, any time connecting the antenna ground to the NEC ground increases noise level, there are other issues in either the homes grounding system or power distribution system that needs careful attention. In closing, I believe that since the beginning of radio the concept of 'ground' has been misunderstood. In the past the deficiencies of a random wire antenna connected to whatever convenient piece of metal that happened to be connected to the ground. In the 1930's concerns about antenna efficiency didn't exist. And even today "efficiency" in it's self is not an issue. In the 30' my father's family had a battery powered MW receiver from Sears. They were deep in the eastern KY hills, with no AC in the county. No telephone. In other words a damn near perfect radio environment. Dad told me stories of the distant stations he received on the 3 stage TRF radio. No local noise, fairly high natural back ground noise, meant the deficiencies meaningless. The same antenna in the same location in the mid 1960's showed the deficiencies imposed serious limitations. My father couldn't understand why my better receiver performed much worse then the older simpler receiver he had used. His mom was a packrat, I am doomed I have the packrat gene from both sides, and still had the receiver. So over the winter of 1967 I rebuilt the receiver. On my home antenna it was clear that my super-het Zenith beat the pants of the Sears TRF. The next summer with a new antenna ran from the same supports my Zenith still beat the Sears hands down. Dad just couldn't understand why the reception was so much worse. Of course the entire county was then wired with AC, telephones and everyone had a TV. And most of the TV's had several hundred feet of twin lead running up the hill sides to antennas mounted up high enough to "see" the distant TV stations. Dad, and I, just didn't understand how much local RF noise had been added. Had I been more knowledgeable I could have realized way back then the importance of proper antenna design and the role antennas can play in fighting RFI. Recently I had a chance to visit Dad's old home, a first cousin still lives there. We took on of our R2000's, and several antennas. The 100' random wire with ground that consisted of the homes NEC grounding system, lighting grounding system and a deep 4" steel well head, that we bonded before my tests, was still a very poor performer. One of Dallas Lankford's active dipoles was best and his 15' relay tuned vertical was a close second. When I added 8 15' radials staked out on the ground the 15' antenna had a slight edge on the active dipole. My cousin has several PCs, several TVs, a DBS and cable TV. Hardly the pristine RF dreamland my dad experienced 70 years ago. So back to the question "What makes a "Good RF Ground?" The sad answer is it depends. For well designed antennas other then random wire, a "Good RF Ground" is simple a safety ground. Assuming the home has a NEC compliant ground system, this will work quiet nicely. If one is insistent on using a ~100' random wire, then something like a whole house ground ring works very well. Rather silly. I know I have one. There are several very weak TIS (low power traffic information stations) that were inaudible with my ~75' random wire antenna. Several summers ago a friend's brother gave me enough 3/8 copper tubing to surround our home, His brother my friend is a commercial electrician and had a Ditch Witch rented for a job that got canceled. Since the client had already paid for the rental, my friend brought it down. He dug an 18~24" trench around our home. We laid the tubing in, and another friend welded the sections into one giant circle. We drove 8' NEC ground rods at the corners and bonded it to the service ground with 4AWG. A neighbor works for a quarry and he brought a dump truck load of ground clay and sand mix down and we back filled the trench with about a foot of the mixture. I laid a soaker hose and we dumped another 6" of the mixture then topped it off the original soil. Another neighbor needed the left over soil to fill in a large depression in his back yard. Think sink hole. I was amazed to receive a 10W TIS from Winchester Ky and another one from Richmond, both about 30 miles away. I visited the Winchester TIS and it is a very poor installation. A 10' whip mounted to a roof top AC air handler. Last summer I received a new TIS like signal on 1640. It is a continuous rebroadcast of the Jackson KY NWS audio stream. Most likely the Irvine KY NOAA WX signal. NOAA doesn't know who is running this, the Richmond DES doesn't know and the Blue Grass Army Depot won't admit that they know anything. Several RDF trips suggest that it is a line source, leaky coax, inside of the Depot near the south west end. This signal is just detectable on a 70' random wire antenna using my "super" ground. It is much stronger, S2, on the Lankford 15' antenna, and better yet with a Lankford 15' antenna with a set of 16' elevated radials. But it is even better with a Lankford Active Dipole and best with the latest Lankford design, an improved derivative of the PA0RDT mounted on the ridge of our metal roof. The roof is grounded, but I suspect the ground is not an issue. A "good rf ground" is only needed with the wrong antenna. If I had a chance to not install my super ground I would clearly avoid the exercise. While it did offer significant improvements in my reception, there are simply better antennas that avoid the need for such extreme efforts. I know I have created a paradox. Simple random wire antennas in very quiet RF locations, with marginal grounds will offer outstanding performance. However in most real world locations, the local noise will be coupled to a random wire antenna unless extreme steps are taken. There are simply better antenna choices that avoid the need for "Good RF Grounds" If the ground, soil, or earth, is such a good conductor, why is the power distributed via metallic conductors and the only use for grounds is for lightning protection and, for the end user, to clear fault conditions. Energy is simple not carried through the ground because the losses would be extremely high. Flame shields up. Terry |
RFI: "Good RF Grounds" [Way too long!]
On Nov 30, 9:14 am, wrote:
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- RF grounding and antenna concepts: Before opening this can of worms I want to explain the steps that lead to this thinking. The following is the result of a casual comment by William Fieldstone. I don't remember the exact question as it was in the middle of a frustrating antenna testing session. But several hours later I was thinking about his basic question and realized that in spite of being a SWL for over 40 years, a ham for over 25 years and an EE, I had never really bothered to think about the random wire antenna that many SWLs use. Perhaps because I started in radio way before I had any understanding and just had never bothered to reconcile the way I treated random antennas and what I knew to be the physics of how antennas operate. Either I can call it an epiphany or, as the new agers would say, a "paradigm shift". Or more likely I had simply been guilty of sloppy or muddled thinking. As I developed the thoughts that follow, I had many conversations with fellow hams, SWLs and some professional engineers that specialize in RF. Some of the conversations got very heated. I was spouting what was viewed as heresy. But after the dust settled everyone agreed with my conclusions. That doesn't mean I am correct, maybe my friends just gave in to my insane ravings to shut me up. I even went back to my college text books and reviewed the section of EM wave theory and antenna function. Before we discuss grounds we need a quick review of how antennas really work. Most of think that 'good RF ground' is a requirement. But stop and think a moment. A TV UHF antenna is a dipole. While we ground such antennas for safety reasons, a ground doesn't effect reception. Hams that operate in the HF, or SW, bands often use dipoles, beams, or loops. None of which need a ground to operate. It is true the ground near the antenna has a pronounced effect on many characteristics such as angle of radiation and to some degree the actual impedance and bandwidth. But a dipole would work just fine in free space. With the exception of 'Long Wire Antennas', Beverage and other surface or traveling wave antennas, all other forms of antennas are either loops or some form of dipoles. Loops and dipoles simply do not need a ground. Back in 1984 I was interested in low power, QRP, Ham HF operations. I used a simple home brew HF transmitter, direct conversion receiver and a dipole. I operated for several weekends from a friend's cabin in the Daniel Boone National Forrest and I used a dipole suspended between two convenient trees. I operated off my motorcycle battery and nothing was grounded. The battery was sitting on a wooden front porch picnic table. I worked 17 countries and 38 states in 3 weekends. While doing some R&D for a commercial WWV receiver installation I experimented with a dipole and a Panasonic RF2300. I was on the metal roof of a manufacturing plant, and I was not connected to ground in any way. And I had very good reception across the HF band with a dipole cut for 10.0MHz Will's question made me realize that with the exception of loops, all of the antennas I normally use are a dipole. In the case of the ever popular random wire antenna, the wire was clearly one element and the earth was the non obvious other half of the dipole. Take a look at any taxi, cop car, fire truck or even a car or truck with a CB. The vertical whip is part of the dipole and the car/truck body is the other part of the dipole. We call such antennas ground planes. A very effective 2M ham antenna can be made with a 19" vertical rod and a 40" diameter metal plate, or picnic table top. A 10 or 11 meter antenna can be created with a ~100" vertical whip and a ~200" metal roof. Both antennas do not need the 'ground plane' connected to the earth. Many hams use vertical antennas and all commercial MW stations in the US use vertical antennas. The FCC requires MW stations to use about 122 radials that form an effective ground plane. A few MW stations use an elevated set of radials that don't need to be grounded for proper operation. For lightning protection a ground is needed, but not for operation. Hams, and SWLs, that use verticals need to have enough radials to reduce the losses caused by poor soil conductivity. A 1/4 wavelength vertical element and an 8' NEC ground rod will be a very poor antenna. The all too common random wire antenna that is using the soil, a poor conductor unless you live in a salt marsh, is a very inefficient antenna. In extremely RF quiet locations such a setup works very well. My friend with the cabin deep in the Daniel Boone National Forrest lets my wife and me spend a week there every fall. There is no electricity, telephone, or cable TV service within a mile or so. In that location, a single random wire antenna, with no feed line, and using the well casing as a ground works VERY well. However at my home, such a setup is an absolute failure. The biggest problem with the all too common random wire antenna is the lack of isolation and the inherent high impedance and the extreme difficulty of achieving sufficient isolation from the noise within the home. So now we come to the main question: "What is a good RF ground?" It depends..... A better first question might "why do I need a good RF ground?" Remember that the earth is almost always an extremely poor conductor. Imagine trying to put up an antenna on a soil less rocky mountain top. Kind of hard to get any sort of ground. I have seen such a location that took a direct lightning strike. Given that lightning has traveled through several thousand feet of the world's best insulator, air, even the poor conductivity of rock looks like a very good ground. The surface of the rock was covered by what physicists call a dendrite pattern. Looked kind of like frost on a window. So why do we insist on trying to use such a poor conductor as part of our antenna system? Habit? Since SWLs typically listen from 100KHz to 30MHz, I am including LW and MW here, and since hams most often operate on a few narrow bands of frequencies the antenna we use are very often very dissimilar. A ham can get by with a couple of dipoles or even a single dipole with "traps" to add additional bands. SWLs can't do that. For a dipole the only ground that is needed is a safety ground. In a proper dipole there will be no ground currents. So if one is going to use a random wire antenna, we need to understand it is a poor compromise but it will work. By adding a 8' NEC ground rod at the feed line end, and by adding as many radials that are as long as feasible, we can boast both the performance of such an antenna, but more importantly we can achieve much higher attenuation of the noise from the home. Let's face it; on lower HF the background noise is high enough so that greater efficiency isn't that helpful. The improved unobvious leg of the dipole, the "ground", would have much better conductivity. But more important the conductivity for efficiency is the improved conductivity converts the pseudo dipole formed by the random wire antenna, into a more effective dipole. And this will allow a better match to the feed line. Better match equals increased isolation can lower the noise from within your home by at least 1 S-unit and many times by 3 or more S-Units. This is manna from heaven. If we decide to go with an active monopole antenna then the ground needs are very similar. Again a 8' NEC ground rod and as many radials as practical will create a "good RF ground. Of course we could forget the grounding rod and just go with a set of elevated radials, or in my case a metal roof and have very good reception. An active dipole doesn't need a ground for operation, although for safety and precipitation static an earth ground is very important. I am not a fan of loops, but if one decides a loop is the way to go, the RF ground really doesn't matter. The feed line does need to be bonded to the NEC required safety ground for lightning protection. In any case, the antenna ground ALWAYS needs to be bonded to the NEC safety ground. If you want to isolate the antenna ground then you need to use a broadband 1:1 RF transformer to achieve electrical isolation between the antenna/ground system and the house NEC ground. In a lightning strike that 1:1 will short and your antenna/ground will become some what connected to the NEC ground. In my experience, any time connecting the antenna ground to the NEC ground increases noise level, there are other issues in either the homes grounding system or power distribution system that needs careful attention. In closing, I believe that since the beginning of radio the concept of 'ground' has been misunderstood. In the past the deficiencies of a random wire antenna connected to whatever convenient piece of metal that happened to be connected to the ground. In the 1930's concerns about antenna efficiency didn't exist. And even today "efficiency" in it's self is not an issue. In the 30' my father's family had a battery powered MW receiver from Sears. They were deep in the eastern KY hills, with no AC in the county. No telephone. In other words a damn near perfect radio environment. Dad told me stories of the distant stations he received on the 3 stage TRF radio. No local noise, fairly high natural back ground noise, meant the deficiencies meaningless. The same antenna in the same location in the mid 1960's showed the deficiencies imposed serious limitations. My father couldn't understand why my better receiver performed much worse then the older simpler receiver he had used. His mom was a packrat, I am doomed I have the packrat gene from both sides, and still had the receiver. So over the winter of 1967 I rebuilt the receiver. On my home antenna it was clear that my super-het Zenith beat the pants of the Sears TRF. The next summer with a new antenna ran from the same supports my Zenith still beat the Sears hands down. Dad just couldn't understand why the reception was so much worse. Of course the entire county was then wired with AC, telephones and everyone had a TV. And most of the TV's had several hundred feet of twin lead running up the hill sides to antennas mounted up high enough to "see" the distant TV stations. Dad, and I, just didn't understand how much local RF noise had been added. Had I been more knowledgeable I could have realized way back then the importance of proper antenna design and the role antennas can play in fighting RFI. Recently I had a chance to visit Dad's old home, a first cousin still lives there. We took on of our R2000's, and several antennas. The 100' random wire with ground that consisted of the homes NEC grounding system, lighting grounding system and a deep 4" steel well head, that we bonded before my tests, was still a very poor performer. One of Dallas Lankford's active dipoles was best and his 15' relay tuned vertical was a close second. When I added 8 15' radials staked out on the ground the 15' antenna had a slight edge on the active dipole. My cousin has several PCs, several TVs, a DBS and cable TV. Hardly the pristine RF dreamland my dad experienced 70 years ago. So back to the question "What makes a "Good RF Ground?" The sad answer is it depends. For well designed antennas other then random wire, a "Good RF Ground" is simple a safety ground. Assuming the home has a NEC compliant ground system, this will work quiet nicely. If one is insistent on using a ~100' random wire, then something like a whole house ground ring works very well. Rather silly. I know I have one. There are several very weak TIS (low power traffic information stations) that were inaudible with my ~75' random wire antenna. Several summers ago a friend's brother gave me enough 3/8 copper tubing to surround our home, His brother my friend is a commercial electrician and had a Ditch Witch rented for a job that got canceled. Since the client had already paid for the rental, my friend brought it down. He dug an 18~24" trench around our home. We laid the tubing in, and another friend welded the sections into one giant circle. We drove 8' NEC ground rods at the corners and bonded it to the service ground with 4AWG. A neighbor works for a quarry and he brought a dump truck load of ground clay and sand mix down and we back filled the trench with about a foot of the mixture. I laid a soaker hose and we dumped another 6" of the mixture then topped it off the original soil. Another neighbor needed the left over soil to fill in a large depression in his back yard. Think sink hole. I was amazed to receive a 10W TIS from Winchester Ky and another one from Richmond, both about 30 miles away. I visited the Winchester TIS and it is a very poor installation. A 10' whip mounted to a roof top AC air handler. Last summer I received a new TIS like signal on 1640. It is a continuous rebroadcast of the Jackson KY NWS audio stream. Most likely the Irvine KY NOAA WX signal. NOAA doesn't know who is running this, the Richmond DES doesn't know and the Blue Grass Army Depot won't admit that they know anything. Several RDF trips suggest that it is a line source, leaky coax, inside of the Depot near the south west end. This signal is just detectable on a 70' random wire antenna using my "super" ground. It is much stronger, S2, on the Lankford 15' antenna, and better yet with a Lankford 15' antenna with a set of 16' elevated radials. But it is even better with a Lankford Active Dipole and best with the latest Lankford design, an improved derivative of the PA0RDT mounted on the ridge of our metal roof. The roof is grounded, but I suspect the ground is not an issue. A "good rf ground" is only needed with the wrong antenna. If I had a chance to not install my super ground I would clearly avoid the exercise. While it did offer significant improvements in my reception, there are simply better antennas that avoid the need for such extreme efforts. I know I have created a paradox. Simple random wire antennas in very quiet RF locations, with marginal grounds will offer outstanding performance. However in most real world locations, the local noise will be coupled to a random wire antenna unless extreme steps are taken. There are simply better antenna choices that avoid the need for "Good RF Grounds" If the ground, soil, or earth, is such a good conductor, why is the power distributed via metallic conductors and the only use for grounds is for lightning protection and, for the end user, to clear fault conditions. Energy is simple not carried through the ground because the losses would be extremely high. Flame shields up. Terry I use a dual band j-pole antenna on 2 meters and 70 cm. It works very well above ground. |
RFI: "Good RF Grounds" [Way too long!]
Cough cough... may I interject?
I am in an urban location and I am in no position to put up a dipole for my SWL needs. The best options as I see them in order of preference are (1) a broadband loop such as a Wellbrook ALA1530+ (2) an Inverted-L (3) a random wire. I have about 5m up and 5m horizontal to play with, so for most HF listening I'm probably going to have a high impedance for the wires and a low one for the loop. From what I've been reading, the random wire in an urban environment is probably the worst of my options, since it will be e-field dominated and pick up all manner of horrific local/near-field noise. That leaves the next option, the inverted-L. The consensus is to use a 9:1 or 3:1 un-un at the base point with a common ground with a coax feeder running back to the shack. I don't see how this would work without at least an attempt at grounding the base of the antenna. Or should I ground the high-impedance winding connected to the L wire and then float the coax that runs back to the RX? The loop is obviously by far the most elegant design, since as you say, it obviates the need for any rf grounding. However, the Wellbrook designs, however wonderful their IMD and nulling are, are a bit pricey for someone who's just bought an SDR-IQ and is thinking about buying a Perseus next month. The inverted-L will cost me about nothing. However, can I emulate a Wellbrook loop with a good Norton amp (either single-ended or push-pull) and my own 1-2m diameter hoop of copper tube (I have loads of 1/2" lying around here)? If I do this, what should I aim for as a middle-of-the-road source impedance from the loop so a can wind the right kind of toriod? (I want to listen from the bottom of the MW band to 10m). Any practical experiences with inverted-L's or untuned loops would be most welcome - since my SDR-IQ will be arriving on Monday and I do need to "get some wire in the air"! Cheers Alex |
RFI: "Good RF Grounds" [Way too long!]
Many thanks for that - I will look at these sources before deciding on a
permanent installation. Cheers Alex |
RFI: "Good RF Grounds" [Way too long!]
On Nov 30, 11:22 pm, Alex wrote:
Many thanks for that - I will look at these sources before deciding on a permanent installation. Cheers Alex Try the simpler antenna in the "Reducing noise" file first. While the specified FET is clearly the best, if you are lucky enough to be far enough from local MW stations, a MPF102 or 2N3819 will work. They are both far from optimal but may be easier to find locally. Terry |
RFI: "Good RF Grounds" [Way too long!]
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RFI: "Good RF Grounds" [Way too long!]
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