|
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! |
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. |
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 |
E/M radiation from a short vertical aerial
On 3/7/2015 6:13 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? 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. What you are not grasping is that these "modes" of transmission have *nothing* to do with the antenna really. As others have said, the antenna only transmits different signal strengths in different directions. How much power sent in a given direction is only loosely connected to how much power ends up in these different reception modes if at all. The real issue is what do you expect to do with these numbers if you have them? I expect that any equations you find for received signal strength will already factor in these relative values giving a received signal strength as a function of *total* power radiated from the antenna. Are you trying to compare the effectiveness of different antenna for different receiving modes? -- Rick |
E/M radiation from a short vertical aerial
On Friday, March 6, 2015 at 7:31:12 PM UTC-6, Jerry Stuckle wrote:
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. The space wave will be quite low angle if working from one point on the earth to another point on the earth. Strictly speaking, a space wave could be at any angle, if you include talking from the earth to someone in space. Earth to ISS is space wave. The signals one receives from a local VHF/UHF FM radio or TV station are space wave. Two CB'ers talking to each other 5 miles apart are using space wave. Only in the case of the earth dweller talking to someone in space, or on the moon, etc would be using a space wave at a higher angle than the usual angle needed for sky wave. And on the high HF bands like 10m, in some cases the angles used for skywave can be fairly low if working DX. But those angles would still likely be a bit higher than terrestrial earth to earth space wave communication. True ground wave, which to me, is the same as the surface wave, actually can follow the curvature of the earth, which a space wave cannot do. But true ground or surface waves are generally only taken advantage of on the lower frequencies such as MW, or LW. But they can be used likely as high as say the 40m band in some cases. I used to have a fairly stout ground wave on 40m when I ran a high ground plane. And I think part of that energy was acting as a surface wave and following the curvature of the earth. The reason I think so, is because the distances I could work with it were a good bit farther than what I would expect with the space wave alone. And I could use the space and surface wave in that case, no matter what time of day or night, or regardless of the conditions needed for sky wave between the two locations. So lots of times during the day when the MUF dropped low enough to lose those people who were 100-150 miles away via sky wave, I was still able to work them via the ground wave. The people using the dipoles and such could hardly hear a peep out of the ones I was working in those cases. And BTW - don't worry about the trolls who have no idea what they are talking about - but insist on showing their ignorance, anyway. We sure wouldn't want to have any of that, now would we.. :/ |
E/M radiation from a short vertical aerial
On Saturday, March 7, 2015 at 6:17:18 PM UTC-6, wrote:
But they can be used likely as high as say the 40m band in some cases. I used to have a fairly stout ground wave on 40m when I ran a high ground plane. And I think part of that energy was acting as a surface wave and following the curvature of the earth. The reason I think so, is because the distances I could work with it were a good bit farther than what I would expect with the space wave alone. BTW, I could have been fooled a bit by refraction.. It is possible for the space wave to go a bit farther than actual line of sight, being as the radio horizon is a bit farther than the visual horizon. Sometimes as much as a third the distance farther. So it's hard to tell for sure which was which on 40m.. True surface wave propagation is great on MW in the daytime.. Night too, except that it's covered up by skywave clutter.. :/ My MW loops were good for receiving that, and I could totally null out a ground/surface wave signal if I felt so compelled. |
E/M radiation from a short vertical aerial
|
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 |
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 |
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 |
E/M radiation from a short vertical aerial
"Spike" wrote in message ... 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 think that Jeff may be on to something. What you need to do is download one of the antenna modeling programs. Set it up for the antenna type you want. Then you can look at the patten and see the take off angle. The take off angle is what determins the ammount of power you have the differant types of propogation. |
E/M radiation from a short vertical aerial
On 08/03/15 12:24, Roger Hayter wrote:
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. But somebody must have done the research, somewhere... An opportunity for some collaborative research between local amateurs? No-one wants to run verticals...too difficult.... A 160m vertical aerial feeding a webSDR, located somewhere near the centre of England, would, using surface (redacted) have a fair-to-considerable percentage coverage of the UK Amateur population and be very useful as a test-bed. Sadly, I don't live near Coventry, although I've been sent there once or twice. The usual webSDRs seem to run on horizontals, unsurprisingly, so not a lot of use for this sort of thing. -- 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 08/03/15 14:22, Ralph Mowery wrote:
I think that Jeff may be on to something. What you need to do is download one of the antenna modeling programs. Set it up for the antenna type you want. Then you can look at the patten and see the take off angle. The take off angle is what determins the ammount of power you have the differant types of propogation. That's an interesting thought, and one that had crossed my mind. However, modelling is only as good as the modeller, and if things are set up to model only the sky-wave component, I might not get the sort of information I'm looking for. BICBW, as I've no experience of this. However, I've just recalled that while researching the topic some time ago, I came across some polar diagrams for cross-field antenna trials in Egypt, which showed the ground/surface wave components as well as the sky wave, the idea being for the MF broadcast band to maximise the former and minimise that latter. Sadly, I didn't keep the url, but it looks like it might be possible to determine some measure of the relative power/field strengths. I'll see if I can find those diagrams, the model used might have been mentioned. -- Spike "Hard cases, it has frequently been observed, are apt to introduce bad law". Judge Rolfe |
E/M radiation from a short vertical aerial
"Spike" wrote in message
... However, I've just recalled that while researching the topic some time ago, I came across some polar diagrams for cross-field antenna trials in Egypt, Take them with a pinch of salt for the trials were discredited because they were conducted withing the near field of a broadcasting mast, ISTR |
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). Yes, there is wide use of the word "waves", but not as you are using it. To answer your question, all you have to know is the frequency, antenna pattern, the current state of the ionosphere, ground conductivity, terrain roughness and the dielectric constant in the area in question. 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. Well, to start with, you get little to no surface wave propagation above about 3 MHz. 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? Once again, all you have to know is the frequency, antenna pattern, the current state of the ionosphere, ground conductivity, terrain roughness and the dielectric constant in the area in question. 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. No, you simply do not understand how propagation works. First read all of this: http://en.wikipedia.org/wiki/Radio_propagation Read the section on Modes very carefully. Follow the links under Modes and read them: http://en.wikipedia.org/wiki/Surface_wave http://en.wikipedia.org/wiki/Skywave http://en.wikipedia.org/wiki/Line-of-sight_propagation http://en.wikipedia.org/wiki/Sporadic_E_propagation http://en.wikipedia.org/wiki/Tropospheric_propagation -- Jim Pennino |
E/M radiation from a short vertical aerial
Roger Hayter wrote:
snip 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? The answer would apply only to one specific antenna at one specfic frequency at one specific location at one specific point in time. The biggest variable in all this is at one point in time. The general approximate answer is: To maximize skywave propagation the antenna main lobe should have an elevation angle of around 20 to 30 degrees and the frequency has to be less than the maximum frequency the ionosphere is currently capable of reflecting. To maximize line of site propagation the antenna main lobe should have an elevation angle as close to zero as possible assuming both ends of the communication are on the Earth. To maximize surface wave propagation the antenna main lobe should have an elevation angle as close to zero as possible and the frequency should be less than 3 MHz. -- Jim Pennino |
E/M radiation from a short vertical aerial
Spike wrote:
On 08/03/15 12:24, Roger Hayter wrote: 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. But somebody must have done the research, somewhere... Thoroughly researched for well over 100 years but you refuse to read the research which says your question in the form it is being asked is meaningless. An opportunity for some collaborative research between local amateurs? No-one wants to run verticals...too difficult.... Vertical antennas have little to nothing to do with the essence of your question. -- Jim Pennino |
E/M radiation from a short vertical aerial
Spike wrote:
On 08/03/15 14:22, Ralph Mowery wrote: I think that Jeff may be on to something. What you need to do is download one of the antenna modeling programs. Set it up for the antenna type you want. Then you can look at the patten and see the take off angle. The take off angle is what determins the ammount of power you have the differant types of propogation. That's an interesting thought, and one that had crossed my mind. However, modelling is only as good as the modeller, and if things are set up to model only the sky-wave component, I might not get the sort of information I'm looking for. BICBW, as I've no experience of this. It is obvious you have no experience. Antenna modeling programs DO NOT MODEL PROPAGATION. Antennas have little to no direct relationship to propagation modes other than putting a main lobe where some particular propagation mode may or may not exist at some particular frequency at some particular point in time. -- Jim Pennino |
E/M radiation from a short vertical aerial
On Sunday, March 8, 2015 at 3:40:21 AM UTC-5, Spike wrote:
On 08/03/15 00:17, wrote: True ground wave, which to me, is the same as the surface wave, actually can follow the curvature of the earth, which a space wave cannot do. But true ground or surface waves are generally only taken advantage of on the lower frequencies such as MW, or LW. That's true, which is a shame as useful ground-wave/surface wave can be had on 28 MHz; a maximum range figure for a path over ground of average conductivity might be 25 miles, and considerably more if the path is over water (especially sea-water). That's space wave on 10m. Even seeing a surface wave on 40m is a bit of a stretch from the norm. As I mentioned in my 2nd post, the reason I saw farther than expected from space wave operation on 40m, could well have been due to refraction of the space wave, and due to the fact that the radio horizon is farther than the visual horizon. I used to work local 10m all the time back in the 80's, early 90's.. 25 miles is fairly easy with any decent antenna, at a decent height above ground. I used to work a good bit farther than that fairly often, when using an antenna at 35-45 feet up. The reason I think so, is because the distances I could work with it were a good bit farther than what I would expect with the space wave alone. Maximum surface wave over ground with average conductivity might be 40 to 45 miles on 40m; if you were getting ranges over this, then your ground conductivity might have been enhanced, or due to the height of your ground-plane, you could have experienced refraction of the space wave. If your location was on a hill-top or other high ground, this could have helped the space wave refraction as well. The ground is good here, and the ground plane was full size at 36 ft at the base of the antenna. But it may well have been an enhanced space wave. I was often working well over 100 miles away in such a case. I believe that the availability 24/7/365 of the space-wave and surface-wave is one of Amateur Radio's undervalued assets. On 160m the surface wave might reach over 100 miles, including behind hills and into valleys, which here in the UK would enable a station to reach a significant proportion of the UK Amateur population. Unfortunately, people dismiss verticals in favour of horizontals of one form or another, the usefulness of which drops to zero when the sky wave disappears (apart from any vertically-polarized radiation from a mismatched feeder or unbalanced elements). Well, not everyone does. I know many on 160m who favor verticals. Not only for ground wave, but better DX. The ground wave is pretty good on 160m if using a vertical. Nearly as good as on the MW AM broadcast band, being the two bands are right next door to each other, so to speak. |
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. Spike, you're a gormless ****. Seriously, you're giving Gareth Alun Evans G4SDW a run for his money here. -- STC // M0TEY // twitter.com/ukradioamateur |
E/M radiation from a short vertical aerial
On Sun, 08 Mar 2015 10:56:58 +0000, Spike wrote:
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). You're digging a deep hole here, Burt. Perhaps it would be better for you to KYGS? |
E/M radiation from a short vertical aerial
On 08/03/15 20:06, wrote:
On Sunday, March 8, 2015 at 3:40:21 AM UTC-5, Spike wrote: On 08/03/15 00:17, wrote: True ground wave, which to me, is the same as the surface wave, actually can follow the curvature of the earth, which a space wave cannot do. But true ground or surface waves are generally only taken advantage of on the lower frequencies such as MW, or LW. That's true, which is a shame as useful ground-wave/surface wave can be had on 28 MHz; a maximum range figure for a path over ground of average conductivity might be 25 miles, and considerably more if the path is over water (especially sea-water). That's space wave on 10m. Even seeing a surface wave on 40m is a bit of a stretch from the norm. As I mentioned in my 2nd post, the reason I saw farther than expected from space wave operation on 40m, could well have been due to refraction of the space wave, and due to the fact that the radio horizon is farther than the visual horizon. I used to work local 10m all the time back in the 80's, early 90's.. 25 miles is fairly easy with any decent antenna, at a decent height above ground. I used to work a good bit farther than that fairly often, when using an antenna at 35-45 feet up. The reason I think so, is because the distances I could work with it were a good bit farther than what I would expect with the space wave alone. Maximum surface wave over ground with average conductivity might be 40 to 45 miles on 40m; if you were getting ranges over this, then your ground conductivity might have been enhanced, or due to the height of your ground-plane, you could have experienced refraction of the space wave. If your location was on a hill-top or other high ground, this could have helped the space wave refraction as well. The ground is good here, With respect, the difference in local ground is rather over stated. Taking the US as an example, the conductivity ranges from 0.5mS to 30mS, which sounds a lot. However, compared to sea water, 5000mS, it is all rather poor. I noticed this some years back when reading a paper, as I recall written by the US Navy, which played down the importance of ground conductivity, other when either at sea or in close proximity to the shore. There is a world atlas of conductivity which is on the web, I can't recall the URL, but it is worth looking out. The various seas and oceans do vary, I recall the Baltic being less conductive for example. Likewise, some of the patterns in the various countries are rather intriguing. Some areas you would expect to be conductive are not. I assume due to local rock formations etc. |
E/M radiation from a short vertical aerial
On 3/8/2015 7:21 PM, Brian Reay wrote:
There is a world atlas of conductivity which is on the web, I can't recall the URL, but it is worth looking out. The various seas and oceans do vary, I recall the Baltic being less conductive for example. Likewise, some of the patterns in the various countries are rather intriguing. Some areas you would expect to be conductive are not. I assume due to local rock formations etc. I've been lurking in this thread and it reminded me of a time many years ago when I was working on a receiver setup. A colleague gave me a book with an equation for signal strength of a signal in the cell phone frequency range in various terrestrial environments. I had a little trouble accepting an arbitrary equation that wasn't at least close to the typical 1/r^2 formula in free space. I seem to recall there was no 1/r^2 term at all rather it was more like a linear or maybe had a rlog(r) term. In any event, no one could explain where the equation came from. I suppose it was an empirical equation rather than something derived from theory. Ignoring waves bounced off the upper atmosphere, I assume the earth acts to help focus the signal and strengthen it close to the ground? -- Rick |
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? I found a reference that says 100% of the signal from an antenna goes into the sky wave, space wave and the ground wave. None of the signal is lost in the transmission process after leaving the antenna. ;) -- Rick |
E/M radiation from a short vertical aerial
On 3/8/2015 4:17 PM, Stephen Thomas Cole wrote:
Spike, you're a gormless ****. Seriously, you're giving Gareth Alun Evans G4SDW a run for his money here. I can see you are right in the running yourself... -- Rick |
E/M radiation from a short vertical aerial
On 3/8/2015 6:56 AM, 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). ....snip... 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 think everyone understands the question just fine. But it is a question without an answer. What you are asking is when you feed a bird, how much of that feed produces crap that lands on your car based on the composition of the feed? If the feed has more fat and less protein does that put more crap on the car or the driveway? -- Rick |
E/M radiation from a short vertical aerial
On Sunday, March 8, 2015 at 6:21:06 PM UTC-5, Brian Reay wrote:
The ground is good here, With respect, the difference in local ground is rather over stated. Maybe so, but not really by me. :| Taking the US as an example, the conductivity ranges from 0.5mS to 30mS, which sounds a lot. However, compared to sea water, 5000mS, it is all rather poor. Sure. It's rated at 30mS here, which was why I said it was "good". And I'm about 55-60 miles from the Gulf of Mexico. I've run mobile from the beach, one time actually backing up to the water and running ground wires into the ocean. Needless to say, my 14 ft tall mobile whip was browning the food quite nicely on that occasion. :) On the Ford truck it was on, it does pretty well even over poor ground, but it really got with the program down at the beach. I was parked at the mouth of the Brazos River down at Quintana Beach. I was also fishing.. I'd rig up my rod and reels, putting them on auto pilot, and then would kick back and drink brewed beverages while jibber jabbering on the radio. :) Mostly 40 and 80 meters. If I saw a rod start to twitch, I'd put down the mike and adult beverage, and reel in the fish. :) I noticed this some years back when reading a paper, as I recall written by the US Navy, which played down the importance of ground conductivity, other when either at sea or in close proximity to the shore. I've never really worried about it too awful much. I don't really rely on it, one way or the other. Even with decent ground quality, I still run a good radial set, or if elevated, enough radials to do the job, as if the ground were poor. Of course, I can't control the ground conductivity away from my QTH. So no use worrying about it. There is a world atlas of conductivity which is on the web, I can't recall the URL, but it is worth looking out. The various seas and oceans do vary, I recall the Baltic being less conductive for example. Likewise, some of the patterns in the various countries are rather intriguing. Some areas you would expect to be conductive are not. I assume due to local rock formations etc. The only map I've seen is one that is in the ARRL handbooks.. It's the one that shows this area as 30 mS. I think it only covered the US, or maybe North America at the max.. Don't know about the rest of the planet. |
E/M radiation from a short vertical aerial
rickman wrote:
On 3/8/2015 4:17 PM, Stephen Thomas Cole wrote: Spike, you're a gormless ****. Seriously, you're giving Gareth Alun Evans G4SDW a run for his money here. I can see you are right in the running yourself... Hey, I'm not the one with the fundamental misunderstanding of radio theory after 50+ years in the hobby. -- STC // M0TEY // twitter.com/ukradioamateur |
E/M radiation from a short vertical aerial
On 3/9/2015 2:26 AM, Stephen Thomas Cole wrote:
rickman wrote: On 3/8/2015 4:17 PM, Stephen Thomas Cole wrote: Spike, you're a gormless ****. Seriously, you're giving Gareth Alun Evans G4SDW a run for his money here. I can see you are right in the running yourself... Hey, I'm not the one with the fundamental misunderstanding of radio theory after 50+ years in the hobby. The problem has nothing to do with radio theory. -- Rick |
E/M radiation from a short vertical aerial
On 09/03/15 00:14, rickman wrote:
On 3/8/2015 6:56 AM, Spike wrote: 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 think everyone understands the question just fine. But it is a question without an answer. But that *is* an answer! What you are saying is that the research remains to be done. What you are asking is when you feed a bird, how much of that feed produces crap that lands on your car based on the composition of the feed? If the feed has more fat and less protein does that put more crap on the car or the driveway? I'd say, based on that, that nutrition science is better understood than the e/m fields emitted by an antenna. -- 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 08/03/15 18:08, Jeff wrote:
Spike, you seem to think that there are different components coming from the antenna that make up the sky-wave component and the ground wave. That is not correct the antenna only radiates one kind of wave (EM). Whether it finds its way to the receiver by sky-wave or ground wave is purely due to what angle the wave hits the atmosphere/ground, and the state of the atmosphere. As an Example take a transmission on top band; during the day normally there will be virtually no sky-wave propagation; use exactly the same set up during the night and there will be considerable sky-wave. I think I knew that, Jeff... If your question is what do you have to do to maximize the ground wave the it is obviously to keep the maxima in the polar diagram as low as possible and don't waste power shooting it at high angles. No, I know how to do that. What I'm after is the relative amounts of power that finish up at the ionosphere, travelling through the atmosphere, and travelling along the surface, for a typical mobile set-up. Of course that is easier said than done, particularly with a mobile where the ground is likely to be poorer than a fixed station with a good ground mat. My initial conditions were a ground of average conductivity. Using something like NEC to model antennas will show the effects of various antenna configurations and ground configurations on the low angles of radiation. But it's only a model, and results depend on how it was constructed. -- Spike "Hard cases, it has frequently been observed, are apt to introduce bad law". Judge Rolfe |
| All times are GMT +1. The time now is 11:40 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com