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E/M radiation from a short vertical aerial
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. My question is: since all these result from the emission of RF from the short rod antenna, what proportions of the total RF power supplied to it are found in each of these three separate waves, and what factors control these proportions? -- Spike "Hard cases, it has frequently been observed, are apt to introduce bad law". Judge Rolfe |
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: Nope; An antenna, any antenna, has a radiation pattern which is a representation of the amount of energy radiated in any particular direction. See this: http://www.antenna-theory.com/basics/radPattern.html The first pattern shown is typical for a vertical antenna. There are no "waves" in the sense you are using the word. -- Jim Pennino |
E/M radiation from a short vertical aerial
On 3/6/2015 6:02 PM, 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. My question is: since all these result from the emission of RF from the short rod antenna, what proportions of the total RF power supplied to it are found in each of these three separate waves, and what factors control these proportions? That depends entirely on the radiation pattern of the antenna. For instance, the sky wave will be that part of the pattern which has fairly high angle of radiation (but lower than the space wave), and the surface wave will have a very low angle of radiation. All of them depend on the characteristics of the antenna, the ground system, the phase of the moon and how you hold your left foot with your right hand when transmitting. What you need to do is model your specific antenna to see what the vertical pattern is in your particular installation. It can vary significantly from one to another. And BTW - don't worry about the trolls who have no idea what they are talking about - but insist on showing their ignorance, anyway. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
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 |
E/M radiation from a short vertical aerial
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. My question is: since all these result from the emission of RF from the short rod antenna, what proportions of the total RF power supplied to it are found in each of these three separate waves, and what factors control these proportions? You are Gareth Alun Evans G4SDW AICMFP. -- STC // M0TEY // twitter.com/ukradioamateur |
E/M radiation from a short vertical aerial
"Spike" wrote in message
... Three different waves will be launched from this: the sky wave, the space wave (including the reflected ray), and the surface wave. Pace that it might propagate in 3 different modes, but only one wave is launched. |
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 |
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? |
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! |
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