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Dave wrote:
the noise is caused by corona on the antenna due to the electric field between the ground and cloud. this field can be many thousands of kv per meter which is enough to cause sharp points and tips of elements to generate corona which makes the hiss and pop noises. Hi Dave, Yeah, that's another hypothesis. One might even be led to reason that insulation would prevent these corona discharges. Yet, it is quite easy to charge a grounded antenna (completely insulated) with the electric field that exists between the ground and clouds (or air masses). So we have at least two candidate causes for what is called by some "precipitation static": charged particles physically impinging on the antenna wire; and electrostatically induced charges that produce corona discharges. Are there others? Can both processes occur simultaneously? Are the two processes simply different paths to the same end: corona discharges? Do we have a way to test these competing hypotheses? 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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"chuck" wrote in message ... Dave wrote: the noise is caused by corona on the antenna due to the electric field between the ground and cloud. this field can be many thousands of kv per meter which is enough to cause sharp points and tips of elements to generate corona which makes the hiss and pop noises. Hi Dave, Yeah, that's another hypothesis. One might even be led to reason that insulation would prevent these corona discharges. Yet, it is quite easy to charge a grounded antenna (completely insulated) with the electric field that exists between the ground and clouds (or air masses). So we have at least two candidate causes for what is called by some "precipitation static": charged particles physically impinging on the antenna wire; and electrostatically induced charges that produce corona discharges. Are there others? Can both processes occur simultaneously? Are the two processes simply different paths to the same end: corona discharges? Do we have a way to test these competing hypotheses? the easiest test is done for us, all we have to do is observe. 'precipitation' static can occur without rain or snow, and it sounds exactly like the noise when there is rain or snow... so i say the corona effect is the major cause and any effect from charged particles is secondary and much smaller. |
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chuck wrote:
Dave wrote: the noise is caused by corona on the antenna due to the electric field between the ground and cloud. this field can be many thousands of kv per meter which is enough to cause sharp points and tips of elements to generate corona which makes the hiss and pop noises. Hi Dave, Yeah, that's another hypothesis. One might even be led to reason that insulation would prevent these corona discharges. Yet, it is quite easy to charge a grounded antenna (completely insulated) with the electric field that exists between the ground and clouds (or air masses). So we have at least two candidate causes for what is called by some "precipitation static": charged particles physically impinging on the antenna wire; and electrostatically induced charges that produce corona discharges. Are there others? Can both processes occur simultaneously? Are the two processes simply different paths to the same end: corona discharges? Do we have a way to test these competing hypotheses? 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- You can easily charge up an insulator with a static charge. A comb is usually made out of an insulating material. Run one through some hair and it will pick up small pieces of paper. (I use my wife's hair.) Secondly, particles don't have to be charged to create a charge on an antenna. They just have to touch it and be pulled off. Google triboelectricity. (I think I spelled that right. If I didn't, ask Cecil how it's spelled. He knows.) Yes, there is more than one way to charge an object to the point of creating corona discharge. Make a small Van de Graf generator and try that. You also might want to charge up an insulator (your comb), touch it to your antenna, and measure how much charge was actually transferred to the antenna. Discharging insulators is sometimes difficult because they're, well, insulators and charge doesn't move around on them readily. Sometimes you have to use Polonium 210, or a torch, or a specially built fan to accomplish this. (You can buy a Polonium brush. The manufacturer warns against taking it apart to see how it works, though.) Make a homemade field mill and measure the earth's electric field during a time when there's corona discharge from your antenna. A large natural electric field from a big, honking thundercloud could easily cause coronal discharge on your antenna under those circumstances. There are lots of things a dedicated amateur can do to measure static electricity, and, if he doesn't get killed, the effort is worth it. Just making up theories out of the clear blue, however, without any attempt to test them, is just a waste of time. 73, Tom Donaly, KA6RUH |
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Tom Donaly wrote:
You can easily charge up an insulator with a static charge. A comb is usually made out of an insulating material. Run one through some hair and it will pick up small pieces of paper. (I use my wife's hair.) Secondly, particles don't have to be charged to create a charge on an antenna. They just have to touch it and be pulled off. Google triboelectricity. (I think I spelled that right. If I didn't, ask Cecil how it's spelled. He knows.) Yes, there is more than one way to charge an object to the point of creating corona discharge. Make a small Van de Graf generator and try that. You also might want to charge up an insulator (your comb), touch it to your antenna, and measure how much charge was actually transferred to the antenna. Discharging insulators is sometimes difficult because they're, well, insulators and charge doesn't move around on them readily. Sometimes you have to use Polonium 210, or a torch, or a specially built fan to accomplish this. (You can buy a Polonium brush. The manufacturer warns against taking it apart to see how it works, though.) Make a homemade field mill and measure the earth's electric field during a time when there's corona discharge from your antenna. A large natural electric field from a big, honking thundercloud could easily cause coronal discharge on your antenna under those circumstances. There are lots of things a dedicated amateur can do to measure static electricity, and, if he doesn't get killed, the effort is worth it. Just making up theories out of the clear blue, however, without any attempt to test them, is just a waste of time. 73, Tom Donaly, KA6RUH Hi Tom, Don't know toward whom your post was directed, but I'll comment anyway --if that's OK. ;-) I'm quite comfortable with your statements on electrostatics. Regarding theories and testing, however, there is perhaps more to be said. A lot of anecdotal evidence of p-static has been described, more or less roughly, in the group. That's really great. But before meaningful tests can be designed, I think an attempt at understanding the mechanisms behind the various p-static reports should be explored. A big part of the problem is that we probably can't cause the p-static to appear on command in our testing laboratories! Moreover, we are pulling stuff out of the air if we believe all reported cases of p-static arise from similar conditions. In more blunt language, I most humbly suggest we seem to be having difficulty understanding what is going on and I hope that the more it is discussed the more likely we can achieve closure. We have, if I am following correctly, at least two suggested causes for the observed phenomena. Charge impingement and electrostatic induction. Yeah, they're both electrostatic actions, but very different. They can even occur simultaneously, which adds additional complication. Moreover, we're concerned with an electrodynamic consequence (a current in the receiver input circuit) of some electrostatic event(s). It is beginning to appear that in some minds, these two explanations are merging: both can cause coronal discharges. I am somewhat skeptical about the induction mechanism, at least in the case of an insulated wire. Here is why: if the field is strong enough to cause coronal discharge of an insulated conductor, it will also cause coronal discharge of almost everything in the vicinity. I think a very strong field would be required for that to occur, surely much more than 10 KV/meter. Didn't W8JI describe something like that with discharges from trees? Electrostatic induction will not generally transfer a charge to an ungrounded conductor. It will simply redistribute the free charges thereon so as to render the net field within the conductor zero. In other words, only charged object(s) brought into direct contact with the conductor will impart a charge. An electroscope comes to mind: bringing a charged comb near the electroscope will cause the leaves to fly outward, but no charge is transferred; the comb (i.e., its field) merely redistributes the charges preexisting on the electroscope. For a grounded wire antenna (even one grounded through the 50 ohm input impedance of the receiver), there is a vast supply of charges that can be "induced" by charged clouds into the conductor from the earth itself. All the free charges in the wire (rather than 50%(?) of them in the insulated case?) may make coronal discharges possible at lesser field strengths. I hope we can continue to kick this around. 73, Chuck NT3G ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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chuck wrote:
So we have at least two candidate causes for what is called by some "precipitation static": charged particles physically impinging on the antenna wire; and electrostatically induced charges that produce corona discharges. Precipitation static requires static transferred from charged particles of rain, snow, or dust. Corona requires the ionization of air. These two phenomena can exist together or separately. Ionization of air requires a certain threshold. Precipitation static can exist either below or that threshold or be the cause of the corona. Corona can exist in the absence of precipitation static. There are other kinds of static, e.g. propagating EM static from numerous sources. -- 73, Cecil, w5dxp.com |
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chuck wrote:
Hi Tom, Don't know toward whom your post was directed, but I'll comment anyway --if that's OK. ;-) I'm quite comfortable with your statements on electrostatics. Regarding theories and testing, however, there is perhaps more to be said. A lot of anecdotal evidence of p-static has been described, more or less roughly, in the group. That's really great. But before meaningful tests can be designed, I think an attempt at understanding the mechanisms behind the various p-static reports should be explored. A big part of the problem is that we probably can't cause the p-static to appear on command in our testing laboratories! Moreover, we are pulling stuff out of the air if we believe all reported cases of p-static arise from similar conditions. In more blunt language, I most humbly suggest we seem to be having difficulty understanding what is going on and I hope that the more it is discussed the more likely we can achieve closure. We have, if I am following correctly, at least two suggested causes for the observed phenomena. Charge impingement and electrostatic induction. Yeah, they're both electrostatic actions, but very different. They can even occur simultaneously, which adds additional complication. Moreover, we're concerned with an electrodynamic consequence (a current in the receiver input circuit) of some electrostatic event(s). It is beginning to appear that in some minds, these two explanations are merging: both can cause coronal discharges. I am somewhat skeptical about the induction mechanism, at least in the case of an insulated wire. Here is why: if the field is strong enough to cause coronal discharge of an insulated conductor, it will also cause coronal discharge of almost everything in the vicinity. I think a very strong field would be required for that to occur, surely much more than 10 KV/meter. Didn't W8JI describe something like that with discharges from trees? Electrostatic induction will not generally transfer a charge to an ungrounded conductor. It will simply redistribute the free charges thereon so as to render the net field within the conductor zero. In other words, only charged object(s) brought into direct contact with the conductor will impart a charge. An electroscope comes to mind: bringing a charged comb near the electroscope will cause the leaves to fly outward, but no charge is transferred; the comb (i.e., its field) merely redistributes the charges preexisting on the electroscope. For a grounded wire antenna (even one grounded through the 50 ohm input impedance of the receiver), there is a vast supply of charges that can be "induced" by charged clouds into the conductor from the earth itself. All the free charges in the wire (rather than 50%(?) of them in the insulated case?) may make coronal discharges possible at lesser field strengths. I hope we can continue to kick this around. 73, Chuck NT3G ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Hi Chuck, Read "Meteorological Aspects of Precipitation Static" By Lieutenant Robert C, Edwards, U.S.N.R., and Captain George W. Brock, U.S.A.A.F. from the Journal of Meteorology, Vol. 1, Number 4, December, 1945. If you Google "Precipitation Static" you can find a pdf file of it. They actually went up in three different airplanes, an RB-37, a B-25D, and a B-17G and did some measurements. You might be interested in their methods and conclusions. 73, Tom Donaly, KA6RUH |
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Cecil Moore wrote:
chuck wrote: So we have at least two candidate causes for what is called by some "precipitation static": charged particles physically impinging on the antenna wire; and electrostatically induced charges that produce corona discharges. Precipitation static requires static transferred from charged particles of rain, snow, or dust. Corona requires the ionization of air. These two phenomena can exist together or separately. Ionization of air requires a certain threshold. Precipitation static can exist either below or that threshold or be the cause of the corona. Corona can exist in the absence of precipitation static. There are other kinds of static, e.g. propagating EM static from numerous sources. -- 73, Cecil, w5dxp.com Many declarative sentences, Cecil, but you're wrong, as usual. When are you going to actually do some meaningful experiments to find out whether you're right or not? 73, Tom Donaly, KA6RUH |
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Tom Donaly wrote:
Hi Chuck, Read "Meteorological Aspects of Precipitation Static" By Lieutenant Robert C, Edwards, U.S.N.R., and Captain George W. Brock, U.S.A.A.F. from the Journal of Meteorology, Vol. 1, Number 4, December, 1945. If you Google "Precipitation Static" you can find a pdf file of it. They actually went up in three different airplanes, an RB-37, a B-25D, and a B-17G and did some measurements. You might be interested in their methods and conclusions. 73, Tom Donaly, KA6RUH Hi Tom, Thanks for the reference. Quite an interesting article. My one problem with it after a quick reading is their autogenous/exogenous electrification dichotomy. More particularly, their notion of exogenous electrification, which " . . . occurs when an aircraft flies through electric fields previously established by a charge separation in the free atmosphere." Not sure it is important to the physics exactly how the electric field was established, but taking the airplane to be an isolated conductor in an electric field, I wonder how "electrification" can take place. Perhaps 60 years ago we used different terminology, but electrification usually refers to contact charge separation. Since there is no assumed contact with charged particles in the exogenous electrification mode, electrification may be a misnomer today. As I suggested in an earlier post, all an electric field can do to an isolated conductor is redistribute the charges preexisting on the conductor. Of course if the redistribution of charges leads to coronal discharges favoring either the positive or negative "end" of the plane, then the plane could acquire a non-zero net charge (i.e., be electrified). The authors don't give a hint that this is what was envisioned, though. I'd appreciate comments on whether such a thing as "exogenous electrification" as described by the authors makes sense to anyone else. 73. Chuck NT3G ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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On Sat, 23 Dec 2006 03:38:18 GMT, "Tom Donaly"
wrote: Cecil Moore wrote: propagating EM static -- you're wrong, as usual. Hi Tom, But always entertaining if you haven't heard the joke before [rare]. 73's Richard Clark, KB7QHC |
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Tom Donaly wrote:
Many declarative sentences, Cecil, but you're wrong, as usual. When are you going to actually do some meaningful experiments to find out whether you're right or not? Where are your experiments that prove you right and me wrong? Where are your references for such? All the experimentation has already been done by others, Tom, and pretty well documented in publications available on the web including a host of governmental and university publications so I would be wasting my time. It is possible that I misunderstood something but impossible that there has not been enough experimentation. Wishing that all static is caused by ionization of the air is just a pipe dream. There would probably never be enough precipitation static on a well-designed folded dipole to result in ionization of the air but certainly enough to hear in a receiver. -- 73, Cecil, w5dxp.com |
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On Sat, 23 Dec 2006 10:02:20 -0500, chuck wrote:
Since there is no assumed contact with charged particles in the exogenous electrification mode, electrification may be a misnomer today. As I suggested in an earlier post, all an electric field can do to an isolated conductor is redistribute the charges preexisting on the conductor. Of course if the redistribution of charges leads to coronal discharges favoring either the positive or negative "end" of the plane, then the plane could acquire a non-zero net charge (i.e., be electrified). The authors don't give a hint that this is what was envisioned, though. Hi Chuck, The author wasn't particularly interested in the electrification as he was the conduction and subsequent discharge. In actuality, what is described as exogenous electrification is no different from autogenous. The air currents described simply convect smaller particles as has been described in subsequent years in other aviation material starting with "Atmospheric Electricity," Chalmers, J.A. - 1967; or earlier with "The Fair Weather Atmospheric Electric Potential and its Gradient," Clark, J.F. 1958. Normal convection builds up a charge stratification on the order of 190 V/m at ground level, but declines to half that a mile up. At that same mile altitude (above ground level) charge density increases 1000%. Needless to say, aircraft at different altitudes in identical, clement weather are subject to vastly different fields. 73's Richard Clark, KB7QHC |
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Richard Clark wrote:
Hi Chuck, The author wasn't particularly interested in the electrification as he was the conduction and subsequent discharge. In actuality, what is described as exogenous electrification is no different from autogenous. The air currents described simply convect smaller particles as has been described in subsequent years in other aviation material starting with "Atmospheric Electricity," Chalmers, J.A. - 1967; or earlier with "The Fair Weather Atmospheric Electric Potential and its Gradient," Clark, J.F. 1958. Normal convection builds up a charge stratification on the order of 190 V/m at ground level, but declines to half that a mile up. At that same mile altitude (above ground level) charge density increases 1000%. Needless to say, aircraft at different altitudes in identical, clement weather are subject to vastly different fields. 73's Richard Clark, KB7QHC Hi Richard, Thanks for the second opinion and additional information. I agree with your interpretation. 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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Cecil Moore wrote: chuck wrote: So we have at least two candidate causes for what is called by some "precipitation static": charged particles physically impinging on the antenna wire; and electrostatically induced charges that produce corona discharges. Precipitation static requires static transferred from charged particles of rain, snow, or dust. Corona requires the ionization of air. These two phenomena can exist together or separately. Ionization of air requires a certain threshold. Precipitation static can exist either below or that threshold or be the cause of the corona. Corona can exist in the absence of precipitation static. There are other kinds of static, e.g. propagating EM static from numerous sources. -- 73, Cecil, w5dxp.com Exactly. Thank you, Cecil. There are many physical mechanisms for generating natural electrical noise. Ask any radio astronomer. 73, Jim AC6XG |
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Cecil Moore wrote:
.. . . All the experimentation has already been done by others, Tom, and pretty well documented in publications available on the web including a host of governmental and university publications so I would be wasting my time. It is possible that I misunderstood something but impossible that there has not been enough experimentation. Wishing that all static is caused by ionization of the air is just a pipe dream. There would probably never be enough precipitation static on a well-designed folded dipole to result in ionization of the air but certainly enough to hear in a receiver. -- 73, Cecil, w5dxp.com Hi Cecil, Though I must seem to be coveting the dead-horse-beating trophy, have you found an explanation of how the relatively low average currents that charged precipitation imparts to an antenna cause static? My back of the envelope calcs showed nanovolt-level signals at the receiver from this current. Clearly, adding charges could eventually result in a corona, but how does the typical current density found in a storm result in measurable (i.e., readily detectable) signals at the receiver front-end when no coronas are present? As I asked in an earlier post, is there a relaxation mechanism somewhere in the antenna/receiver system? Where? What determines its time constants? Are the reported current densities wrong (i.e., not representative of the conditions under which non-coronal p-static is typically developed)? Is p-static somehow anomalous in that it is not found in all storms with charged precipitation? The coronal mechanism is understandable to me, but the non-coronal p-static leaves me needing a better explanation than I have been able to find. A special thanks to you for helping to keep the group lively and interesting, Cecil! 73, Chuck NT3G ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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Here's a link to a brief Navy document (gotta be true!) that gives a
simple overview of noise. It claims coronal discharges are the principal cause of precipitation static. No mention, however, of any other, non-principal causes. http://www.globalsecurity.org/milita...14030_ch10.pdf 14030_ch10.pdf (application/pdf Object) Evidently, aircraft encounter current densities between 50-300 A/square meter, while typical current densities near the ground from charged precipitation are on the order of 1 uA/square meter. That's quite a few orders of magnitude difference. http://www.jya.com/mil-std-464.htm MIL-STD-464 Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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On Sun, 24 Dec 2006 08:31:56 -0500, chuck wrote:
My back of the envelope calcs showed nanovolt-level signals at the receiver from this current. Hi Chuck, From the nature of your questions that follow, your envelope appears to be insufficient to cover the topic. Clearly, adding charges could eventually result in a corona, but how does the typical current density found in a storm result in measurable (i.e., readily detectable) signals at the receiver front-end when no coronas are present? As I asked in an earlier post, is there a relaxation mechanism somewhere in the antenna/receiver system? Where? What determines its time constants? There are two mechanisms at work, and they are classically the source and the load. The source imparts an impulse, the load provides a complex response. Any impulse's origin is the arrival of a charge. The load (the antenna feeding the receiver) is very large in comparison to the volume of charge arriving and all impulses are not coherent. Your nano-volt determination appears to neglect the accumulation of charges which, in turn, does not take into account the reactance of the load (there has to be a considerable mismatch involved here). 73's Richard Clark, KB7QHC |
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chuck wrote:
Though I must seem to be coveting the dead-horse-beating trophy, have you found an explanation of how the relatively low average currents that charged precipitation imparts to an antenna cause static? My back of the envelope calcs showed nanovolt-level signals at the receiver from this current. Someone reported being able to hear each individual large snowflake. Could be that the amount of charge in a large snowflake or a large piece of dust is magnitudes higher than in a drop of rain, which I assume is the charge you are talking about above. In any case, a very large number of particles hitting around the same time could have a cumulative effect. I personally have never heard P-static from rain but I think I have seen it remembered on the bandscope on my IC-756PRO. -- 73, Cecil http://www.w5dxp.com |
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Cecil Moore wrote:
Someone reported being able to hear each individual large snowflake. Could be that the amount of charge in a large snowflake or a large piece of dust is magnitudes higher than in a drop of rain, which I assume is the charge you are talking about above. In any case, a very large number of particles hitting around the same time could have a cumulative effect. I personally have never heard P-static from rain but I think I have seen it remembered on the bandscope on my IC-756PRO. This study found that 20% of the observed charges were greater than 1.6 pC. Or, 80% were below 1.6 pC. At least it doesn't contradict your hypothesis. http://adsabs.harvard.edu/abs/1981PhDT.......149B Collection of Electric Charge Information on Snowflakes in the Field. 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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Cecil Moore wrote:
... Makes you wish we could shoot 'em through a darn cloud chamber! grin Regards, JS |
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Richard Clark wrote:
There are two mechanisms at work, and they are classically the source and the load. The source imparts an impulse, the load provides a complex response. Any impulse's origin is the arrival of a charge. The load (the antenna feeding the receiver) is very large in comparison to the volume of charge arriving and all impulses are not coherent. Your nano-volt determination appears to neglect the accumulation of charges which, in turn, does not take into account the reactance of the load (there has to be a considerable mismatch involved here). 73's Richard Clark, KB7QHC I'm not sure of the numbers involved, but as someone who has lived in a 300 inch of snow per season and storms with up to 10 inch/hour plus high winds, that snow static is real and a real pain in the ass. It makes small pops as it hits, and eventually you will hear a large amount of noise apparently from discharge. Dependant on antenna type, etc. I have no experience with dust. tom K0TAR |
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chuck wrote:
This study found that 20% of the observed charges were greater than 1.6 pC. Or, 80% were below 1.6 pC. At least it doesn't contradict your hypothesis. Let me make it clear that virtually all of my precipitation static experience has been with wind-blown dust in the Arizona desert with absolutely no personal experience with snow static and very little with rain static. All I know about snow and rain static is what I have read and heard. Here in East Texas, rain is usually preceded by lightning so precipitation noise from rain is hard to detect. I think I saw it on the bandscope display of my IC-756PRO the other day, didn't see any lightning or hear any thunder but, of course, I can't say for certain. However, I can say with certainty that precipitation static from wind-blown dust can exist on a low humidity clear-sky day and was somewhat proportional to wind speed. Changing over from a bare-wire dipole to an insulated folded dipole reduced the problem to a tolerable level. The folded dipole was less noisy on dry windy days than a bare-wire dipole with a 4:1 voltage balun (DC short) on the feedline. I can't swear that corona didn't exist during receive, but I never saw any glow at night even when I was transmitting 500 watts. Corona should be less of a problem in low humidity like Arizona. -- 73, Cecil http://www.w5dxp.com |
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Tom Ring wrote:
I'm not sure of the numbers involved, but as someone who has lived in a 300 inch of snow per season and storms with up to 10 inch/hour plus high winds, that snow static is real and a real pain in the ass. It makes small pops as it hits, and eventually you will hear a large amount of noise apparently from discharge. Dependant on antenna type, etc. Tom, do you have any experience with bare-wire dipoles Vs insulated folded dipoles? I have no experience with dust. Add your snow static experience to my dust static experience and all we need is someone with rain static experience. :-) -- 73, Cecil http://www.w5dxp.com |
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chuck wrote:
This study found that 20% of the observed charges were greater than 1.6 pC. Or, 80% were below 1.6 pC. At least it doesn't contradict your hypothesis. One other thought based on Richard C's comments: Your calculation didn't take reflections in a resonant antenna system into account which could cause the maximum voltage to be a couple of magnitudes larger at the antinodes. That assumes the burst of RF from the discharge is a few cycles long at the resonant frequency. As an IEEE paper says, resonance can cause "voltage magnification by coherent spatial modes". -- 73, Cecil http://www.w5dxp.com |
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Jim Kelley wrote:
Exactly. Thank you, Cecil. There are many physical mechanisms for generating natural electrical noise. Ask any radio astronomer. But I suspect the died-in-the-wool corona-ites would argue that all EM noise is caused by corona even if it originally occurred on another heavenly body. Speaking of which, do you think Miss America's aura is caused by corona? -- 73, Cecil http://www.w5dxp.com |
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OK, lets try to model the fundamental phenomena we're talking about and
try to understand them in terms of simple electrostatic principles. We start with these assumptions: 1. Vertical antenna of length l 2. Antenna grounded at base 3. Ideal RF current sensor at base (i.e., receiver) 4. Complete absence of electrostatic fields except from #5 below 5. A single negative charge Q that can be moved from infinity to actual contact with the antenna. 6. Electromagnetic effects of a moving charge are not considered; they do exist, of course, so reader beware. We start by placing the charge Q at infinity so that there is no net charge on the antenna. As Q is brought near the antenna, its field will cause a redistribution of charges on the antenna. Because the antenna is connected to the earth at its base, a negative charge will flow into the earth from the antenna. This will result in the antenna having a net positive charge Q' such that |Q'||Q| (i.e., the closer the charge is to the antenna, the smaller the difference between Q' and Q, and in the limit, they are equal). The negative charge flowing to earth causes a current to be detected by the RF current sensor at the base of the antenna. As the charge moves closer and ultimately touches the antenna, a movement of exactly -Q into the earth is completed, with the result that the antenna once again has a net charge of zero and from the moment of impact, no further charge redistributions or currents take place. Note that in this model, the signal we hear is actually generated by the approach of the charge, rather than by its actual physical presence on the antenna. (Consider the effect of insulated wire with this model.) This is the specific mechanism in the model by which a charge colliding with the antenna causes a quantifiable current in the receiver. Our objective is to get a handle on the waveshape (risetime, peak, etc.) of this current; i.e., can it be detected by a receiver as a noise impulse? The waveshape of the current pulse will be determined mainly by 1) the magnitude of the charge; 2) the time required for the charge redistribution to propagate through the antenna; and 3) the velocity with which the charge approaches the antenna. We know the magnitude of the charge by construction and assume propagation of the charge redistribution (i.e., we are not talking about charge carrier drift) at the speed of light. The critical element, of course, is the velocity of the charge as it approaches the antenna. The lower its velocity, the longer the risetime of the induced current pulse. If Q is attached to a snowflake with a velocity of one mile per hour, the current peak will be quite low because the charge redistribution will occur over a relatively long time period. But if we assume the charge velocity is so high that the other factors establish risetime, we can estimate some of the interesting pulse parameters. For example, if the antenna is conveniently 1/100 mile long and Q = 1 pC, we get a peak current on the order of 20 uA. If our receiver front end is 50 ohms, that peak current would generate a 1 mV peak voltage pulse with a negligible risetime. (Please check my arithmetic) I think the model shows this to be the highest peak current attainable (under quite unrealistic assumptions). If the rise-time of the current pulse depends on the particle's velocity, then it is not clear how that pulse's peak amplitude can be increased. I'm not persuaded that resonance is relevant, particularly since so much of the noise we are discussing is very broadband. We can explore the number of charges that must arrive in some time window to achieve a given combined pulse magnitude at the receiver. First, however, someone who has not forgotten his math and physics should algebraically relate pulse risetime and peak value to charge velocity. Then we would have an indication of the detectability of a single charge striking an antenna. We could predict the magnitude of the charge and/or the velocity needed to achieve some specified signal level at the input of the receiver. This relationship has not yet been presented and without it, understanding of the possibility of non-coronal precipitation static remains elusive. Are there other approaches to quantitative demonstrations out there? Does someone have an alternative model of how a charge striking an antenna is translated into a detectable signal? Have fun! 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
folded dipoles
chuck wrote:
... understanding of the possibility of non-coronal precipitation static remains elusive. Please note that human understanding is not necessary for something to exist and denying its existence because of a lack of understanding doesn't make it go away. It is what it is. -- 73, Cecil http://www.w5dxp.com |
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"Cecil Moore" wrote in message t... chuck wrote: Though I must seem to be coveting the dead-horse-beating trophy, have you found an explanation of how the relatively low average currents that charged precipitation imparts to an antenna cause static? My back of the envelope calcs showed nanovolt-level signals at the receiver from this current. Someone reported being able to hear each individual large snowflake. Could be that the amount of charge in a large snowflake or a large piece of dust is magnitudes higher than in a drop of rain, which I assume is the charge you are talking about above. In any case, a very large number of particles hitting around the same time could have a cumulative effect. I personally have never heard P-static from rain but I think I have seen it remembered on the bandscope on my IC-756PRO. -- 73, Cecil http://www.w5dxp.com My first experience with p-static was with snow in Norway 1984. The air was very cold and dry before it started snowing it seemed like at first you could hear each flake that hit the wire then finally it just became a rushing sound. |
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"Jimmie D" wrote in message .. . "Cecil Moore" wrote in message t... chuck wrote: Though I must seem to be coveting the dead-horse-beating trophy, have you found an explanation of how the relatively low average currents that charged precipitation imparts to an antenna cause static? My back of the envelope calcs showed nanovolt-level signals at the receiver from this current. Someone reported being able to hear each individual large snowflake. Could be that the amount of charge in a large snowflake or a large piece of dust is magnitudes higher than in a drop of rain, which I assume is the charge you are talking about above. In any case, a very large number of particles hitting around the same time could have a cumulative effect. I personally have never heard P-static from rain but I think I have seen it remembered on the bandscope on my IC-756PRO. -- 73, Cecil http://www.w5dxp.com My first experience with p-static was with snow in Norway 1984. The air was very cold and dry before it started snowing it seemed like at first you could hear each flake that hit the wire then finally it just became a rushing sound. I ve been trying to piece together what everyone has been saying about it with my own experience. So far I suspect that the weather must be fairly dry just before the precipitation starts. |
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Cecil Moore wrote:
chuck wrote: ... understanding of the possibility of non-coronal precipitation static remains elusive. Please note that human understanding is not necessary for something to exist and denying its existence because of a lack of understanding doesn't make it go away. It is what it is. Nicely said, Cecil. Hope you didn't get the impression I was denying the existence of non-coronal p-static, or attempting to make it go away. But I hope you'll agree that to be detected in a receiver, the static has to have a certain amplitude. We know what that amplitude is and we know the kinds of charges scientists have measured on precipitation as well as typical current densities. What is elusive is how the charges get changed into a detectable signal. Hardly metaphysics, and no more intended to attain Human Understanding than the application of Ohm's law! ;-) Actually, I was trying to provide a basis or framework within which non-coronal static could be analyzed. Except for the unfortunate paragraph with hypothetical numbers (the sad result of an embarrassing senior moment) the rest seems a reasonable start. Will you tell me again how we know that non-coronal p-static exists? Without that information we need to say "It is what it is iff it exists", no? ;-) 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
folded dipoles
chuck wrote:
What is elusive is how the charges get changed into a detectable signal. Yes, there's a broad range of possible explanations. One interesting theory is that uncharged particles rubbing against an uncharged antenna results in a triboelectric effect that, after contact, leaves the antenna and particles with opposite charges. You might call it the relativity theory of charged particles. :-) Will you tell me again how we know that non-coronal p-static exists? By definition, corona requires ionization of the air which requires a certain current through the air, i.e. at least a small arc. The question is, can p-static exist and be heard below the corona threshold? In 1939, another C. Moore, W9LZX, solved the corona problem at HCJB in Quito, Ecuador by inventing the cubical quad antenna. Describing the problem with the Yagi beam: "Gigantic corona discharges sprang full- blown from the tips of the driven element and directors, standing out in mid-air and burning with a wicked hiss and crackle. The heavy industrial aluminum tubing used for the elements of the doomed beam glowed with the heat of the arc and turned incandescent at the tips. Large molten chunks of aluminum dropped to the ground as the inexorable fire slowly consumed the antenna. The corona discharges were so loud and so intense that they could be seen and heard singing and burning a quarter- mile away from the station." So Clarence Moore invented the cubical quad to solve the corona problem. One must admit that the cubical quad at least reduced the corona problem by many magnitudes during transmit. One must also admit that the corona problem during receive is magnitudes below the problem during transmit. At some level, the air ceases to be ionized and corona ceases to exist, by definition. What can we conclude by applying the principle of antenna transmit/receive reciprocity? Comparing the Yagi to the cubical quad is similar to comparing a single-wire 1/2WL dipole to a full-wave loop. The ground referenced loop with its rounded corners certainly reduces the corona threshold level. It is possible that the loop is quieter *because* it is below the corona threshold and the single-wire dipole is not. Can we hear p-static on a full-wave loop? Yes, I have heard it on a clear-sky, low-humidity, windy day in the Arizona desert. Did it occur without ionization of the air? There probably were no points (pun intended) in the system conducive to corona discharge. Obviously a qualitative argument rather than a quantitative one but possibly valid nonetheless based on the Quito experience. -- 73, Cecil http://www.w5dxp.com |
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"chuck" wrote in message ... Cecil Moore wrote: chuck wrote: ... understanding of the possibility of non-coronal precipitation static remains elusive. Please note that human understanding is not necessary for something to exist and denying its existence because of a lack of understanding doesn't make it go away. It is what it is. Nicely said, Cecil. Hope you didn't get the impression I was denying the existence of non-coronal p-static, or attempting to make it go away. But I hope you'll agree that to be detected in a receiver, the static has to have a certain amplitude. We know what that amplitude is and we know the kinds of charges scientists have measured on precipitation as well as typical current densities. What is elusive is how the charges get changed into a detectable signal. Hardly metaphysics, and no more intended to attain Human Understanding than the application of Ohm's law! ;-) Actually, I was trying to provide a basis or framework within which non-coronal static could be analyzed. Except for the unfortunate paragraph with hypothetical numbers (the sad result of an embarrassing senior moment) the rest seems a reasonable start. Will you tell me again how we know that non-coronal p-static exists? Without that information we need to say "It is what it is iff it exists", no? ;-) i have a feeling that what you will find is that the individual charges on drops, flakes, and dust is too small to be detected by a normal amateur receiver. However, the electric field that must accompany them is what generates the corona effects that can be heard. Just think about it, how do small particles get charged without also generating a larger bulk field? The effect that charges the particles, be it dry friction from wind on dust, or freezing and convection in clouds (any cloud, not just those with enough charge to generate lightning) is not an individual particle effect, it happens to many, many particles at once which cumulatively create a much larger electric field than any one of them alone could create. And while the charge transfer of small drops striking a conductor may not be enough to stimulate a receiver the corona caused by the accumulated field over the whole height of the structure can be significant. |
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"Cecil Moore" wrote in message . .. chuck wrote: What is elusive is how the charges get changed into a detectable signal. By definition, corona requires ionization of the air which requires a certain current through the air, i.e. at least a small arc. The question is, can p-static exist and be heard below the corona threshold? corona is not an 'arc', an arc is normally between two conductors. corona is a local cascade breakdown in air as electrons are accelerated enough so that when they colide with another molecule of the air they can knock off more electrons. That is why there is a threshold voltage for corona inception, below a given field strength the electrons can't gain enough energy to sustain the breakdown. note that the shape of the conductor is very important in this process also, a blunt smooth surface will produce smaller fields and have a higher inception voltage than a sharp point because the field gets concentrated more around the point and thus requires a lower voltage to start corona breakdown. What can we conclude by applying the principle of antenna transmit/receive reciprocity? in this case, nothing. the tx problem was because the rf voltage at the antenna tips was high enough to cause corona on a massive scale. rf voltage on a receiving antenna is miniscule and so can not be the source of corona... this means other sources, not related to rf and the intended use of the structure as an antenna, are the cause. |
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Dave wrote:
However, the electric field that must accompany them is what generates the corona effects that can be heard. Wouldn't the whole sky glow at night like the Northern Lights if the entire dust cloud was ionizing the air to the corona threshold? The fair weather current doesn't meet the corona threshold so how could corona occur with a rounded full-wave loop under fair weather conditions? -- 73, Cecil http://www.w5dxp.com |
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Dave wrote:
note that the shape of the conductor is very important in this process also, a blunt smooth surface will produce smaller fields and have a higher inception voltage than a sharp point because the field gets concentrated more around the point and thus requires a lower voltage to start corona breakdown. So the sharp ends of a single-wire dipole would be more conducive to corona than would a rounded full-wave loop. Would you say that an antenna without corona is quieter than an antenna with corona? -- 73, Cecil http://www.w5dxp.com |
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"Cecil Moore" wrote in message m... Dave wrote: However, the electric field that must accompany them is what generates the corona effects that can be heard. Wouldn't the whole sky glow at night like the Northern Lights if the entire dust cloud was ionizing the air to the corona threshold? no, the field in the air is below the threshold. it is the concentrated field around objects that cause the field to exceed the threshold. The fair weather current doesn't meet the corona threshold so how could corona occur with a rounded full-wave loop under fair weather conditions? the fair weather current and the field that drives it is fairly small, not normally enough to cause corona or we would be hearing it all the time. |
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"Cecil Moore" wrote in message ... Dave wrote: note that the shape of the conductor is very important in this process also, a blunt smooth surface will produce smaller fields and have a higher inception voltage than a sharp point because the field gets concentrated more around the point and thus requires a lower voltage to start corona breakdown. So the sharp ends of a single-wire dipole would be more conducive to corona than would a rounded full-wave loop. Would you say that an antenna without corona is quieter than an antenna with corona? of course. we see that here all the time, the top antenna of a stack can be very noisy with corona, but those lower down on the tower (even though they are getting hit by the same rain/snow) are quiet. |
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Dave wrote:
i have a feeling that what you will find is that the individual charges on drops, flakes, and dust is too small to be detected by a normal amateur receiver. However, the electric field that must accompany them is what generates the corona effects that can be heard. Just think about it, how do small particles get charged without also generating a larger bulk field? The effect that charges the particles, be it dry friction from wind on dust, or freezing and convection in clouds (any cloud, not just those with enough charge to generate lightning) is not an individual particle effect, it happens to many, many particles at once which cumulatively create a much larger electric field than any one of them alone could create. And while the charge transfer of small drops striking a conductor may not be enough to stimulate a receiver the corona caused by the accumulated field over the whole height of the structure can be significant. Charges can be accumulated on objects so as to produce a corona breakdown in many ways. I think this is one of our fundamental starting points and hopefully, was never in question. The separation of charges can be accomplished by a variety of techniques, not all well-understood. A moving cloud of charged particles can induce very large charges into a grounded conductor. A sufficient concentration of charge at pointed components of the conductor will produce a corona. The corona plainly radiates "noise" that is detected by our receivers. There is less certainty about whether an ungrounded conductor (say, an unattached wire) can be made to produce a corona via electrostatic induction. As I wrote in an earlier post in this thread, an ungrounded conductor cannot be charged by an external field, but the distribution of charges preexisting on the conductor can be affected by the field, perhaps causing coronal discharges. I recall writing that uneven discharges of the positive and negative "ends" of the conductor could even leave the conductor with a net charge. Your points are good ones, Dave, and worth keeping in mind. 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
folded dipoles
"chuck" wrote in message ... Dave wrote: i have a feeling that what you will find is that the individual charges on drops, flakes, and dust is too small to be detected by a normal amateur receiver. However, the electric field that must accompany them is what generates the corona effects that can be heard. Just think about it, how do small particles get charged without also generating a larger bulk field? The effect that charges the particles, be it dry friction from wind on dust, or freezing and convection in clouds (any cloud, not just those with enough charge to generate lightning) is not an individual particle effect, it happens to many, many particles at once which cumulatively create a much larger electric field than any one of them alone could create. And while the charge transfer of small drops striking a conductor may not be enough to stimulate a receiver the corona caused by the accumulated field over the whole height of the structure can be significant. Charges can be accumulated on objects so as to produce a corona breakdown in many ways. I think this is one of our fundamental starting points and hopefully, was never in question. The separation of charges can be accomplished by a variety of techniques, not all well-understood. A moving cloud of charged particles can induce very large charges into a grounded conductor. A sufficient concentration of charge at pointed components of the conductor will produce a corona. The corona plainly radiates "noise" that is detected by our receivers. There is less certainty about whether an ungrounded conductor (say, an unattached wire) can be made to produce a corona via electrostatic induction. As I wrote in an earlier post in this thread, an ungrounded conductor cannot be charged by an external field, but the distribution of charges preexisting on the conductor can be affected by the field, perhaps causing coronal discharges. I recall writing that uneven discharges of the positive and negative "ends" of the conductor could even leave the conductor with a net charge. Your points are good ones, Dave, and worth keeping in mind. floating conductors can definitely create corona. this can be seen in corona camera pictures of power line insulators and other hardware that is insulated but still in the high field near a power line. even water drops on insulators can cause corona in a very strong field. and even if you get away from power line stuff, a leyden jar has an insulated conductor and it can obviously be charged, as can aircraft... and if they accumulate enough charge they can cause corona. |
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Dave wrote:
"chuck" wrote in message ... Dave wrote: i have a feeling that what you will find is that the individual charges on drops, flakes, and dust is too small to be detected by a normal amateur receiver. However, the electric field that must accompany them is what generates the corona effects that can be heard. Just think about it, how do small particles get charged without also generating a larger bulk field? The effect that charges the particles, be it dry friction from wind on dust, or freezing and convection in clouds (any cloud, not just those with enough charge to generate lightning) is not an individual particle effect, it happens to many, many particles at once which cumulatively create a much larger electric field than any one of them alone could create. And while the charge transfer of small drops striking a conductor may not be enough to stimulate a receiver the corona caused by the accumulated field over the whole height of the structure can be significant. Charges can be accumulated on objects so as to produce a corona breakdown in many ways. I think this is one of our fundamental starting points and hopefully, was never in question. The separation of charges can be accomplished by a variety of techniques, not all well-understood. A moving cloud of charged particles can induce very large charges into a grounded conductor. A sufficient concentration of charge at pointed components of the conductor will produce a corona. The corona plainly radiates "noise" that is detected by our receivers. There is less certainty about whether an ungrounded conductor (say, an unattached wire) can be made to produce a corona via electrostatic induction. As I wrote in an earlier post in this thread, an ungrounded conductor cannot be charged by an external field, but the distribution of charges preexisting on the conductor can be affected by the field, perhaps causing coronal discharges. I recall writing that uneven discharges of the positive and negative "ends" of the conductor could even leave the conductor with a net charge. Your points are good ones, Dave, and worth keeping in mind. floating conductors can definitely create corona. this can be seen in corona camera pictures of power line insulators and other hardware that is insulated but still in the high field near a power line. even water drops on insulators can cause corona in a very strong field. and even if you get away from power line stuff, a leyden jar has an insulated conductor and it can obviously be charged, as can aircraft... and if they accumulate enough charge they can cause corona. Hi Dave, A leyden jar is, of course, a capacitor. It is charged by grounding the outside, applying a charge to the inside conductor, and then removing the ground. Hope I didn't cause anyone to suspect that a capacitor could not be charged that way. Recall that in electrostatic induction, we always ground the conductor, bring a field near it, and then remove the ground connection. A net charge then remains on the conductor even after the inducing field is moved away. Aircraft can be and are regularly charged by the triboelectric effect. The issue I raised is whether they can be given a net charge by immersion in an electric field. I also tried to explain that it is possible for a floating conductor to produce a coronal discharge without that conductor having a net charge, and followed with the suggestion that the act of producing a differential coronal discharge might itself result in a net charge on the conductor, but the corona can be produced by the field even when the conductor is not charged. Your power line example may be a good example of coronal discharge of a floating conductor in a strong field, but we probably don't know if it ever had a net charge on it due to the field. Hope this clarifies my thoughts a little. ;-) 73, Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
folded dipoles
On Mon, 25 Dec 2006 23:10:00 -0600, Cecil Moore
wrote: chuck wrote: ... understanding of the possibility of non-coronal precipitation static remains elusive. Please note that human understanding is not necessary for something to exist and denying its existence because of a lack of understanding doesn't make it go away. It is what it is. Amen, Cecil! Anyone who has lived in central Texas and is an active ham has experienced all sorts of extraordinary noises....corona discharges, precipitation static, and others.... which can be experienced on a clear day, cloudy day, rainy day, dusty day....though I would hasten to add that the most dramatic noise performances occurred with an approaching weather front of some kind and *are* probably corona discharges. Other noises that I experienced while trying to work DX were not so easily identifiable as corona. I haven't experienced the same noises here in Virginia. Here, I get little in the way of warning, other than normal crashes of static, before hearing a loud *bang* of thunder indicating that I should disconnect aerials and vacate the shack!. One other empirical data point...all of the above mentioned noises were *dramatically* reduced when switching from plumbers-delight, yagi antennas to closed loop, cubical quads. Always. Despite the fact that many have insisted that quads aren't "quieter" than yagis, it's my story and I'm sticking to it. I use yagis now. If I lived in Texas, I would probably be using quads again. 73, Ken K4XL *** BoatAnchor Manual Archive *** On the web at http://bama.sbc.edu and http://bama.edebris.com FTP site info: bama.sbc.edu login: anonymous p/w: youremailadr |
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