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#1
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E/M radiation from a short vertical aerial
In rec.radio.amateur.antenna Spike wrote:
Imagine a short rod vertical aerial not connected to ground, for the (say) 160/80/60/40m bands, as might be found in a typical /M set-up, fed with RF energy and operating over ground of average conductivity. Three different waves will be launched from this: the sky wave, the space wave (including the reflected ray), and the surface wave. Each of these have their own characteristics, inasmuch as the sky wave is launched willy-nilly even if the band isn't open for that mode, the space wave depends on the path to the receiver, and the surface wave depends on the electromagnetic characteristics of the air and the surface material, although to some extent the latter affects all the waves generated. These "waves" are actually called skywave and surface wave and are a propagation phenomena. See: http://en.wikipedia.org/wiki/Skywave http://en.wikipedia.org/wiki/Surface_wave http://en.wikipedia.org/wiki/Line-of-sight_propagation for how signals propagate. -- Jim Pennino |
#3
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E/M radiation from a short vertical aerial
Spike wrote:
On 07/03/15 01:49, wrote: In rec.radio.amateur.antenna Spike wrote: Imagine a short rod vertical aerial not connected to ground, for the (say) 160/80/60/40m bands, as might be found in a typical /M set-up, fed with RF energy and operating over ground of average conductivity. Three different waves will be launched from this: the sky wave, the space wave (including the reflected ray), and the surface wave. Each of these have their own characteristics, inasmuch as the sky wave is launched willy-nilly even if the band isn't open for that mode, the space wave depends on the path to the receiver, and the surface wave depends on the electromagnetic characteristics of the air and the surface material, although to some extent the latter affects all the waves generated. These "waves" are actually called skywave and surface wave and are a propagation phenomena. See: http://en.wikipedia.org/wiki/Skywave http://en.wikipedia.org/wiki/Surface_wave http://en.wikipedia.org/wiki/Line-of-sight_propagation for how signals propagate. Thanks to you and Jerry Stuckle for your replies. Since a vertical aerial that I described initially emits all three of these waves, I was interested in the relative amounts of the RF power supplied to the antenna that goes into each. For example, does the sky wave component take 90% of the power, leaving 10% for the space and surface waves? What phenomena control this? You've totally missed the point. These "wave" phenomena are determined by the frequency and the condition of the ionosphere, which is influenced by solar radiation. A transmitting antenna knows nothing about any type of propagation. The amount of any type of "wave" propagation that will happen depneds on the antenna pattern, i.e. how much energy is radiated in any particular direction, and the current ionospheric conditions. There is a rule of thumb that says that maximum skywave occurs at an antenna main lobe elevation of about 30 degrees, but it is only a general rule of thumb. The exact angle will be determined by the frequency and current condition of the ionosphere. -- Jim Pennino |
#4
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E/M radiation from a short vertical aerial
On 07/03/15 09:34, Jeff wrote:
Since a vertical aerial that I described initially emits all three of these waves, I was interested in the relative amounts of the RF power supplied to the antenna that goes into each. For example, does the sky wave component take 90% of the power, leaving 10% for the space and surface waves? What phenomena control this? You are missing the point Spike, the antenna has no knowledge of how the power that it radiates will propagate. It all depends on how much power leaves the antenna at what angle, and what angle the antenna is positioned relative to ground. All the antenna has is a polar response of how much power is radiated at what angle. It is that angle and the way the atmosphere reacts at any particular time that controls the propagation of waves. This can vary with time of day etc. What controls the polar diagram is the physical dimensions of the antenna, the height above ground, the conductivity of the ground, the proximity of other objects, and other factors. Thanks for the comments, Jeff. Perhaps I'm not being clear enough. Look at the issue this way.... While it's clear that the totality of the e/m emissions from from the antenna depend on factors such as length, height, and ground, (and I originally assumed a particular set-up in the OP) there are three distinct methods by which such a transmission can be received: the sky wave path to a distant receiver, a space wave to a line-of-sight receiver (that could easily be outside the surface wave range) and the surface wave to a receiver tucked into the far side of a hill with no sky wave or space wave path. It can be expected that increasing the transmit power will increase the received signal at all three locations, but the question I'd like to see answered is: what proportion of the power supplied to the antenna goes to each of these three phenomena, which all arise every time the transmitter is keyed. They might all be connected by the conditions you mention, I'm not suggesting they aren't, but for the set-up I originally described, what are the proportions of the power supplied to the antenna that contribute to each? Or, to put it in yet another way...There might only be one 'wave' launched from the set-up, that propagates in three different 'modes' (for the want of a better word); so what controls the relative power/energy with which each 'mode' is propagated? The case I'm particularly interested in is the short-rod vertical not connected to ground, in the MF/low-HF bands, as might be found in a /M set-up. -- Spike "Hard cases, it has frequently been observed, are apt to introduce bad law". Judge Rolfe |
#5
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E/M radiation from a short vertical aerial
On 3/7/2015 5:13 AM, Spike wrote:
On 07/03/15 09:34, Jeff wrote: Since a vertical aerial that I described initially emits all three of these waves, I was interested in the relative amounts of the RF power supplied to the antenna that goes into each. For example, does the sky wave component take 90% of the power, leaving 10% for the space and surface waves? What phenomena control this? The antenna emits only one wave. It is its environment that determines the strength at any distant point. You are missing the point Spike, the antenna has no knowledge of how the power that it radiates will propagate. It all depends on how much power leaves the antenna at what angle, and what angle the antenna is positioned relative to ground. All the antenna has is a polar response of how much power is radiated at what angle. It is that angle and the way the atmosphere reacts at any particular time that controls the propagation of waves. This can vary with time of day etc. What controls the polar diagram is the physical dimensions of the antenna, the height above ground, the conductivity of the ground, the proximity of other objects, and other factors. Thanks for the comments, Jeff. Perhaps I'm not being clear enough. That's because you have a misunderstanding of radiation through a medium. Look at the issue this way.... While it's clear that the totality of the e/m emissions from from the antenna depend on factors such as length, height, and ground, (and I originally assumed a particular set-up in the OP) there are three distinct methods by which such a transmission can be They are not distinct. They merge and separate based on the environment in which they exist. received: the sky wave path to a distant receiver, a space wave to a line-of-sight receiver (that could easily be outside the surface wave range) and the surface wave to a receiver tucked into the far side of a hill with no sky wave or space wave path. It can be expected that increasing the transmit power will increase the received signal at all three locations, but the question I'd like to see answered is: what proportion of the power supplied to the antenna goes to each of these three phenomena, which all arise every time the transmitter is keyed. They might all be connected by the conditions you mention, I'm not suggesting they aren't, but for the set-up I originally described, what are the proportions of the power supplied to the antenna that contribute to each? Or, to put it in yet another way...There might only be one 'wave' launched from the set-up, that propagates in three different 'modes' (for the want of a better word); so what controls the relative power/energy with which each 'mode' is propagated? There are no 'modes'. The wave is affected by its environment. It is impossible to know what the signal strength at a distant point without knowing all the characteristics of the medium through which it passes. The case I'm particularly interested in is the short-rod vertical not connected to ground, in the MF/low-HF bands, as might be found in a /M set-up. What is a /M setup? |
#6
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E/M radiation from a short vertical aerial
On Sat, 07 Mar 2015 08:18:00 -0600, John S wrote:
What is a /M setup? Mobile as in M0WYM/M Charlie. M0WYM. -- Hello Wisconsin! |
#7
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E/M radiation from a short vertical aerial
"Spike" wrote in message ... Thanks for the comments, Jeff. Perhaps I'm not being clear enough. Look at the issue this way.... While it's clear that the totality of the e/m emissions from from the antenna depend on factors such as length, height, and ground, (and I originally assumed a particular set-up in the OP) there are three distinct methods by which such a transmission can be received: the sky wave path to a distant receiver, a space wave to a line-of-sight receiver (that could easily be outside the surface wave range) and the surface wave to a receiver tucked into the far side of a hill with no sky wave or space wave path. It can be expected that increasing the transmit power will increase the received signal at all three locations, but the question I'd like to see answered is: what proportion of the power supplied to the antenna goes to each of these three phenomena, which all arise every time the transmitter is keyed. They might all be connected by the conditions you mention, I'm not suggesting they aren't, but for the set-up I originally described, what are the proportions of the power supplied to the antenna that contribute to each? Or, to put it in yet another way...There might only be one 'wave' launched from the set-up, that propagates in three different 'modes' (for the want of a better word); so what controls the relative power/energy with which each 'mode' is propagated? You have to get it in your head there is not 3 differant waves launched from the antenna. There is only one wave. As it leaves the antenna, whatever the wave hits determins if it is ground, sky or whatever. The patern of the antenna determins how much goes where. With some antennas the patern is such much of it goes out to the horizon and not much up in the air. Others radiate much to the vertical and not much toward the horizon. Think of it as throwing a rock into the middle a small pond. If there is noting in the pond, the wave will go out toward the edges equally. If that same rockis thrown in near the edge of the pond, some of the ripples will n hit th eedge of the pond near the rock first while it will take some time for the ripples to hit the other side. You have the same origional wave, but its propogation is modified as to where it is at . You do not have seperate waves leaving the rock. |
#8
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E/M radiation from a short vertical aerial
On 07/03/15 15:57, Ralph Mowery wrote:
"Spike" wrote Or, to put it in yet another way...There might only be one 'wave' launched from the set-up, that propagates in three different 'modes' (for the want of a better word); so what controls the relative power/energy with which each 'mode' is propagated? You have to get it in your head there is not 3 differant waves launched from the antenna. There is only one wave. As it leaves the antenna, whatever the wave hits determins if it is ground, sky or whatever. The patern of the antenna determins how much goes where. With some antennas the patern is such much of it goes out to the horizon and not much up in the air. Others radiate much to the vertical and not much toward the horizon. Think of it as throwing a rock into the middle a small pond. If there is noting in the pond, the wave will go out toward the edges equally. If that same rockis thrown in near the edge of the pond, some of the ripples will n hit th eedge of the pond near the rock first while it will take some time for the ripples to hit the other side. You have the same origional wave, but its propogation is modified as to where it is at . You do not have seperate waves leaving the rock. Thanks for the explanation and illustration. Amateur (and professional) literature abounds with terms like sky wave, space wave, and surface wave. There are sky wave radars, space wave radars, and surface wave radars, for example. It isn't unreasonable to use these as descriptors of what I was trying to find out. This was, to recap, the relative proportions of the RF power delivered to the aerial for each of these (whatever one wants to call them), for a typical /M (mobile) set-up on the MF and low HF bands operating over ground of average conductivity, a near everyday occurrence in the Amateur community. The mechanism for the single wave that's transmitted resulting in (whatever one wants to call them) isn't really of interest, but the relative proportions that wind up in (whatever one wants to call them) are. In terms of your analogy, the rock being thrown into the pool close to one edge of the pond is the equivalent of the short rod /M aerial operating close to the ground, mounted on the vehicle. I can imagine that if the edge of the pond is a gentle sandy slope, the reflected waves will be different in nature that if the edge of the pond is a vertical rock. However, this is merely reflecting the different ground conductivities that might be experienced in the real-life Amateur situation: some energy will go skywards to a distant receiver, some will travel through air to a line-of-sight receiver, and some will go to a receiver in the shadow of a hill that cannot receive either of the other two (whatever one wants to call them). -- Spike "Hard cases, it has frequently been observed, are apt to introduce bad law". Judge Rolfe |
#9
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E/M radiation from a short vertical aerial
On 08/03/15 09:33, Jeff wrote:
Spike wrote I think you are coming at this from the wrong view point. Perhaps the question that you should be asking is what take-off angles are required to produce maximum ground wave, and how do you maximize that for a MF mobile installation. I'm really after figures for the proportions of the RF power fed to that antenna, that finish up in whatever 'they' are called (the use of the well-known word 'waves' seem to upset people despite their having been used for the specifics I mentioned, for about 100 years). I'm aware that reconfiguring the set-up might affect these proportions, but I did refer the original query to a typical /M (mobile) set-up of a short rod antenna not connected to ground and operating over average conductivity in the MF/low-HF bands. For example, does 40% power the sky (redacted), another 40% power the space (redacted), and the other 20% power the surface (redacted)? Clearly, 100% of the RF power goes somewhere, and the various parts of it must add up to 100% - so what are the proportions? If the /M (mobile) set-up was changed to a /P (portable) one with a 5/8 lambda ground-mounted antenna, the sky (redacted) proportion would lower and the surface/space (redacted) would increase - but from what to what? I'm beginning to think that this topic is either so simple or so complex that most Amateurs have either forgotten it or have never heard of it. -- Spike "Hard cases, it has frequently been observed, are apt to introduce bad law". Judge Rolfe |
#10
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E/M radiation from a short vertical aerial
Spike wrote:
On 08/03/15 09:33, Jeff wrote: Spike wrote I think you are coming at this from the wrong view point. Perhaps the question that you should be asking is what take-off angles are required to produce maximum ground wave, and how do you maximize that for a MF mobile installation. I'm really after figures for the proportions of the RF power fed to that antenna, that finish up in whatever 'they' are called (the use of the well-known word 'waves' seem to upset people despite their having been used for the specifics I mentioned, for about 100 years). I'm aware that reconfiguring the set-up might affect these proportions, but I did refer the original query to a typical /M (mobile) set-up of a short rod antenna not connected to ground and operating over average conductivity in the MF/low-HF bands. For example, does 40% power the sky (redacted), another 40% power the space (redacted), and the other 20% power the surface (redacted)? Clearly, 100% of the RF power goes somewhere, and the various parts of it must add up to 100% - so what are the proportions? If the /M (mobile) set-up was changed to a /P (portable) one with a 5/8 lambda ground-mounted antenna, the sky (redacted) proportion would lower and the surface/space (redacted) would increase - but from what to what? I'm beginning to think that this topic is either so simple or so complex that most Amateurs have either forgotten it or have never heard of it. I suspect that the sort of precision with which one can measure signal strength. plus very local variations of surface wave intensity due to varying ground conditions, mean that it would be hard to know if the signal level resulted from, say, one, five or fifty percent of the transmitted power. So I suspect your question has never been answered. An opportunity for some collaborative research between local amateurs? -- Roger Hayter |
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