The antenna in my post is a self-resonant top-loaded monopole 12.4 m in height. This is quite a lot longer than the Part 15 AM limit, but Trainotti is only concerned with short monopoles for licensed AM broadcasting. Trainotti prefers getting resonance with top loading, because this is more efficient than using a loading coil. Sufficient top loading to get resonance would probably not be permitted by the Part 15 rules.
Other information published by Trainotti indicates that ground resistance increases with antenna height. So, a 3 m monopole may give less ground resistance than what I reported in my post. It's too bad that Trainotti was not interested in doing ground resistance calculations specifically for Part 15 AM. He could have provided really useful information about antenna system design for us.
The antenna in my post is a self-resonant top-loaded monopole 12.4 m in height. This is quite a lot longer than the Part 15 AM limit, but Trainotti is only concerned with short monopoles for licensed AM broadcasting. Trainotti prefers getting resonance with top loading, because this is more efficient than using a loading coil. Sufficient top loading to get resonance would probably not be permitted by the Part 15 rules.
Other information published by Trainotti indicates that ground resistance increases with antenna height. So, a 3 m monopole may give less ground resistance than what I reported in my post. It's too bad that Trainotti was not interested in doing ground resistance calculations specifically for Part 15 AM. He could have provided really useful information about antenna system design for us.
We are all, indeed, fortunate that Prof. Valentin Trainotti, the world's foremost authority on short MW AM antennas, has agreed to take a look at the Part 15 AM antenna problem. Until now, Prof. Trainotti has worked on short antenna projects for licensed AM BCB stations, but he has not yet worked on Part 15 antennas. What he has agreed to do was theoretically design a "Standard Part 15 AM Antenna" that can serve as a reference for designing other Part 15 antennas. The Standard Antenna is so conservatively designed that there can be little doubt about its legality. Of course, there is no actual guarantee of its legality, because the design has not been reviewed or approved by the FCC. However, care has been taken to remove as many possible objections as could be reasonably anticipated. What follows is an edited version of Prof. Trainotti's report:
"The Part 15 AM monopole, operating at 1.7 MHz, 3 meters in height, can be made from an aluminum tube, 50 mm (about 2") in diameter. Three or four dacron ropes can be guys. An Artificial Ground Plane mounted below the base of the monopole, 3 meters in diameter, is made of metal, like chicken wire or copper. There is a Natural Ground Plane extending a half wavelength, 88.17 meters, in all directions from the base of the monopole. The radiation resistance of the monopole is Rr = 0.114 ohms, and the antenna capacitive reactance is Xa = 2600 ohms.
"In order to resonate this monopole, an inductor of reactance XL = 2600 ohms has to be put in series with the antenna leads. The inductor will be installed between the transmitter hot lead and the antenna hot lead. A metal box containing the inductor should have a generous size in order not to significantly reduce the tuning coil Q. A circuit for impedance matching the transmitter output to the tuning coil input can be installed in the same box. It is important for the transmitter to be well-shielded in order not to get RF into the Audio System.
"The electrical properties of the soil are considered to be:
"Wet Soil; Conductivity 0.03 S/m, Relative Permittivity 20, Ground Plane Resistance, Rgp= 2.00 ohms.
"Average Soil; Conductivity 0.01 S/m, Relative Permittivity 10, Rgp = 3.47 ohms.
"Dry Soil; Conductivity .001 S/m, Relative Permittivity 4, Rgp = 10.97 ohms.
"The tuning coil Qs, and their equivalent series resistances, are Q = 400, RL = 6.5 ohms; Q = 200, RL = 13 ohms; Q = 100, RL = 26 ohms.
"Tuning coil inductance is L = 243.4 uH.
"Antenna efficiency is Rr/(Rr + RL + Rgp).
"If the transmitter efficiency is 25%, 25 mW will be applied to the antenna. The following gives the radiated power, Pr, in uW, and the fields strength, E, in mV/m at 100 meters for the various combinations of Loading coil Q and soil type:
"Q = 400
"Wet Soil, Pr = 325, E = 1.71
Average Soil, Pr = 275, E = 1.58
Dry Soil, Pr = 150, E = 1.20
"Q = 200
"Wet Soil, Pr = 188, E = 1.30
Average Soil, Pr = 170, E = 1.24
Dry Soil, Pr = 118, E = 1.03
"Q = 100
"Wet Soil, Pr = 100, E = 0.95
Average Soil, Pr = 95, E = 0.93
Dry Soil, Pr = 78, E = 0.83
"As can be seen, most of the time, the tuning inductor has a resistance, RL, higher than the ground plane resistance, Rgp. Although the area of the artificial ground plane is small, its low resistance dominates the total ground plane resistance. The input resistance of the antenna is highly dependent on the Q of the tuning coil.
"The tuning inductor can be installed in a metal box connected directly to the metallic Artificial Ground Plane. The 100 mW transmitter can also be connected on the metallic ground plane, and directly to the tuning inductor. The transmitter is likely to be very small compared to the tuning inductor and the metal box that contains it."
We are all, indeed, fortunate that Prof. Valentin Trainotti, the world's foremost authority on short MW AM antennas, has agreed to take a look at the Part 15 AM antenna problem. Until now, Prof. Trainotti has worked on short antenna projects for licensed AM BCB stations, but he has not yet worked on Part 15 antennas. What he has agreed to do was theoretically design a "Standard Part 15 AM Antenna" that can serve as a reference for designing other Part 15 antennas. The Standard Antenna is so conservatively designed that there can be little doubt about its legality. Of course, there is no actual guarantee of its legality, because the design has not been reviewed or approved by the FCC. However, care has been taken to remove as many possible objections as could be reasonably anticipated. What follows is an edited version of Prof. Trainotti's report:
"The Part 15 AM monopole, operating at 1.7 MHz, 3 meters in height, can be made from an aluminum tube, 50 mm (about 2") in diameter. Three or four dacron ropes can be guys. An Artificial Ground Plane mounted below the base of the monopole, 3 meters in diameter, is made of metal, like chicken wire or copper. There is a Natural Ground Plane extending a half wavelength, 88.17 meters, in all directions from the base of the monopole. The radiation resistance of the monopole is Rr = 0.114 ohms, and the antenna capacitive reactance is Xa = 2600 ohms.
"In order to resonate this monopole, an inductor of reactance XL = 2600 ohms has to be put in series with the antenna leads. The inductor will be installed between the transmitter hot lead and the antenna hot lead. A metal box containing the inductor should have a generous size in order not to significantly reduce the tuning coil Q. A circuit for impedance matching the transmitter output to the tuning coil input can be installed in the same box. It is important for the transmitter to be well-shielded in order not to get RF into the Audio System.
"The electrical properties of the soil are considered to be:
"Wet Soil; Conductivity 0.03 S/m, Relative Permittivity 20, Ground Plane Resistance, Rgp= 2.00 ohms.
"Average Soil; Conductivity 0.01 S/m, Relative Permittivity 10, Rgp = 3.47 ohms.
"Dry Soil; Conductivity .001 S/m, Relative Permittivity 4, Rgp = 10.97 ohms.
"The tuning coil Qs, and their equivalent series resistances, are Q = 400, RL = 6.5 ohms; Q = 200, RL = 13 ohms; Q = 100, RL = 26 ohms.
"Tuning coil inductance is L = 243.4 uH.
"Antenna efficiency is Rr/(Rr + RL + Rgp).
"If the transmitter efficiency is 25%, 25 mW will be applied to the antenna. The following gives the radiated power, Pr, in uW, and the fields strength, E, in mV/m at 100 meters for the various combinations of Loading coil Q and soil type:
"Q = 400
"Wet Soil, Pr = 325, E = 1.71
Average Soil, Pr = 275, E = 1.58
Dry Soil, Pr = 150, E = 1.20
"Q = 200
"Wet Soil, Pr = 188, E = 1.30
Average Soil, Pr = 170, E = 1.24
Dry Soil, Pr = 118, E = 1.03
"Q = 100
"Wet Soil, Pr = 100, E = 0.95
Average Soil, Pr = 95, E = 0.93
Dry Soil, Pr = 78, E = 0.83
"As can be seen, most of the time, the tuning inductor has a resistance, RL, higher than the ground plane resistance, Rgp. Although the area of the artificial ground plane is small, its low resistance dominates the total ground plane resistance. The input resistance of the antenna is highly dependent on the Q of the tuning coil.
"The tuning inductor can be installed in a metal box connected directly to the metallic Artificial Ground Plane. The 100 mW transmitter can also be connected on the metallic ground plane, and directly to the tuning inductor. The transmitter is likely to be very small compared to the tuning inductor and the metal box that contains it."
Ermi about a suggested Standard Part 15 AM Antenna: The Standard Antenna is so conservatively designed that there can be little doubt about its legality. Of course, there is no actual guarantee of its legality, because the design has not been reviewed or approved by the FCC. However, care has been taken to remove as many possible objections as could be reasonably anticipated. What follows is an edited version of Prof. Trainotti's report:
"...The Part 15 AM monopole, operating at 1.7 MHz, 3 meters in height, can be made from an aluminum tube, 50 mm (about 2") in diameter. Three or four dacron ropes can be guys. An Artificial Ground Plane mounted below the base of the monopole, 3 meters in diameter, is made of metal, like chicken wire or copper. There is a Natural Ground Plane extending a half wavelength, 88.17 meters, in all directions from the base of the monopole." ...
________
While in the last paragraph Dr Trainotti states that the metal box with the coil, and the transmitter can be connected "directly" to the metallic ground plane, he does not state the physical location of those components with respect to that ground plane.
From the description given for this Standard Antenna, the 3-meter monopole, coil and transmitter could be mounted an arbitrary distance above the Artificial Ground Plane, and connect to it directly using a long conducting path (short ground lead plus "massive" ground wire/metal pole/flagpole/billboard steel, etc). That path, of course, becomes a significant radiating component of the antenna, which can have a great affect on the radiation efficiency of the functional r-f system (see note below)
For example, 25 milliwatts of applied power, a coil Q of 200, and 3.47 ohm r-f ground resistance in the Standard Antenna system produce a 1.24 millivolt/meter groundwave field at 100 meters, according to the quoted post. This is a reasonable field value for those conditions if the base of the Standard Antenna, and the Artificial Ground Plane are mounted within a few inches of the physical earth.
However if the transmitter, coil and antenna are elevated some 20 feet or more above the Artificial Ground Plane, then radiation from the extended length of the conductor(s) connecting the transmitter chassis to that ground plane could increase the field strength at 100 meters by a factor of 5 or more. This is the equivalent of applying 25 X or more transmitter power to the antenna system when the base of the monopole is within a few inches of the physical earth, when using that Artificial Ground Plane either on, or buried in the earth.
If for the assumed average conditions (coil Q of 200, 3.47 ohm r-f ground loss, and 25 milliwatts of applied power), a 1.24 millivolt/meter field at 100 meters can be considered a "benchmark" for a Standard Antenna on 1.7 MHz, then the inverse distance groundwave field at 1 mile would be about 80 microvolts/meter (excluding earth conductivity losses). Of interest then is that this field would not provide good service to a typical indoor AM radio in an urban environment, which even in a non-urban area with low electrical noise can require several hundred microvolts/meter for (barely) acceptable performance.
This tends to show that Part 15 AM transmit systems claiming/producing a useful coverage radius of several miles would be using systems that could not be "reasonably anticipated" to meet the parameters of this Standard system -- for which "little doubt about its legality" is claimed in the post.
Of course everyone is free to install and use whatever system they choose, but maybe the information here will be useful in making such decisions.
Note: The paper at http://filebay1.home.comcast.net/~filebay1/Elevated_Part_15_AM_Antennas.pdf shows why this is true for elevated antennas.
//
Ermi about a suggested Standard Part 15 AM Antenna: The Standard Antenna is so conservatively designed that there can be little doubt about its legality. Of course, there is no actual guarantee of its legality, because the design has not been reviewed or approved by the FCC. However, care has been taken to remove as many possible objections as could be reasonably anticipated. What follows is an edited version of Prof. Trainotti's report:
"...The Part 15 AM monopole, operating at 1.7 MHz, 3 meters in height, can be made from an aluminum tube, 50 mm (about 2") in diameter. Three or four dacron ropes can be guys. An Artificial Ground Plane mounted below the base of the monopole, 3 meters in diameter, is made of metal, like chicken wire or copper. There is a Natural Ground Plane extending a half wavelength, 88.17 meters, in all directions from the base of the monopole." ...
________
While in the last paragraph Dr Trainotti states that the metal box with the coil, and the transmitter can be connected "directly" to the metallic ground plane, he does not state the physical location of those components with respect to that ground plane.
From the description given for this Standard Antenna, the 3-meter monopole, coil and transmitter could be mounted an arbitrary distance above the Artificial Ground Plane, and connect to it directly using a long conducting path (short ground lead plus "massive" ground wire/metal pole/flagpole/billboard steel, etc). That path, of course, becomes a significant radiating component of the antenna, which can have a great affect on the radiation efficiency of the functional r-f system (see note below)
For example, 25 milliwatts of applied power, a coil Q of 200, and 3.47 ohm r-f ground resistance in the Standard Antenna system produce a 1.24 millivolt/meter groundwave field at 100 meters, according to the quoted post. This is a reasonable field value for those conditions if the base of the Standard Antenna, and the Artificial Ground Plane are mounted within a few inches of the physical earth.
However if the transmitter, coil and antenna are elevated some 20 feet or more above the Artificial Ground Plane, then radiation from the extended length of the conductor(s) connecting the transmitter chassis to that ground plane could increase the field strength at 100 meters by a factor of 5 or more. This is the equivalent of applying 25 X or more transmitter power to the antenna system when the base of the monopole is within a few inches of the physical earth, when using that Artificial Ground Plane either on, or buried in the earth.
If for the assumed average conditions (coil Q of 200, 3.47 ohm r-f ground loss, and 25 milliwatts of applied power), a 1.24 millivolt/meter field at 100 meters can be considered a "benchmark" for a Standard Antenna on 1.7 MHz, then the inverse distance groundwave field at 1 mile would be about 80 microvolts/meter (excluding earth conductivity losses). Of interest then is that this field would not provide good service to a typical indoor AM radio in an urban environment, which even in a non-urban area with low electrical noise can require several hundred microvolts/meter for (barely) acceptable performance.
This tends to show that Part 15 AM transmit systems claiming/producing a useful coverage radius of several miles would be using systems that could not be "reasonably anticipated" to meet the parameters of this Standard system -- for which "little doubt about its legality" is claimed in the post.
Of course everyone is free to install and use whatever system they choose, but maybe the information here will be useful in making such decisions.
Note: The paper at http://filebay1.home.comcast.net/~filebay1/Elevated_Part_15_AM_Antennas.pdf shows why this is true for elevated antennas.
//
When I read through the description, I assumed that it was referring to the base of the antenna and the artificial groundplane as being on (or at least very near) ground level because of the mention of:
"There is a Natural Ground Plane extending a half wavelength, 88.17 meters, in all directions from the base of the monopole."
To me that implied that the base of the monopole antenna would be at ground level (or very near)?
But perhaps I'm naive on what constitutes a "natural groundplane" in this sort of case. Could someone clarify that term for me, please?
Daniel
When I read through the description, I assumed that it was referring to the base of the antenna and the artificial groundplane as being on (or at least very near) ground level because of the mention of:
"There is a Natural Ground Plane extending a half wavelength, 88.17 meters, in all directions from the base of the monopole."
To me that implied that the base of the monopole antenna would be at ground level (or very near)?
But perhaps I'm naive on what constitutes a "natural groundplane" in this sort of case. Could someone clarify that term for me, please?
Daniel
The reason for placing the loading coil of the hypothetical "standard antenna" in a metal box is to assure its legality to the extent that it is possible. Suggestions have been made that the wording of Section 15.219(b) might require that the total length of the loading coil wire is to be included in the 3 meter length limitation if the loading coil were mounted along the length of the antenna. By including the loading coil in a metal box that is part of the transmitter assembly, such as is done in the LPB AM-2000 and the Rangemaster AM-1000, such an objection is prevented. The FCC has apparently not ruled on this subject.
Since preventing potential legal objections is a principal consideration in Trainotti's "standard antenna," controversial structures like elevated antennas are not considered for the standard antenna model.
The Natural Ground Plane includes the soil, extending a half wavelength from the base of the antenna, where there is a return path of the RF displacement current from the monopole back to the base of the antenna.
The reason for placing the loading coil of the hypothetical "standard antenna" in a metal box is to assure its legality to the extent that it is possible. Suggestions have been made that the wording of Section 15.219(b) might require that the total length of the loading coil wire is to be included in the 3 meter length limitation if the loading coil were mounted along the length of the antenna. By including the loading coil in a metal box that is part of the transmitter assembly, such as is done in the LPB AM-2000 and the Rangemaster AM-1000, such an objection is prevented. The FCC has apparently not ruled on this subject.
Since preventing potential legal objections is a principal consideration in Trainotti's "standard antenna," controversial structures like elevated antennas are not considered for the standard antenna model.
The Natural Ground Plane includes the soil, extending a half wavelength from the base of the antenna, where there is a return path of the RF displacement current from the monopole back to the base of the antenna.
"By including the loading coil in a metal box that is part of the transmitter assembly, such as is done in the LPB AM-2000 and the Rangemaster AM-1000, such an objection is prevented. The FCC has apparently not ruled on this subject."
I *think* the Rangemaster's box is fiberglass (1/4" thick, made in Germany?), though my memory could be mistaken on that point.
However, mounting the loading coil in a metal box with the transmitter could have some advantages over an exposed coil. First one I can think of is rain. Some may live in more arid climates, but at least some of us live where there is a considerable amount of precipitation. I'm not certain, but I would think that water trickling down the coil or dampness on the coil could affect the tuning of the antenna since water doesn't have the same dielectric coefficient as air there is some capacitance between turns? I know that with CB (11 meter) operation, water getting into an antenna's loading coil generally drastically affects the swr until it dries back out. Even when it is not actively raining, I would think that dampness between and under the wires of a coil wound on something like PVC (for example) would have an affect on the tuning, and in damp weather could take days or weeks to dry out fully.
Another consideration would be security. A coil inside a box would be better protected from vandalism and etc.
Also it *might* make tuning easier by eliminating some of the hand/body capacitance at least in the region of the loading coil.
As to it being acually necessary/desirable from the FCC POV? Perhaps, I can't say for certain. But considering the Rangemaster has it's loading coil inside the same non-metal box as the transmitter and was certified, and considering that I do not recall any FCC field actions which mention the presence of a loading coil as grounds for a NOUO/NAL/Citation, I'm not seeing the logic for it as a priority. As already mentioned, however, I can see other possible reasons where it could be perhaps advantageous.
Thank you for the explanation of natural groundplane. My next question regarding the natural groundplane is does it exist when there is no wired connection between the transmitter and the ground? If, for example, a battery operated transmitter and attached antenna is hung from a weather balloon or something so the lowest part is 10 ft from the ground, would the earth still act as a natural groundplane? Would there be a difference as the balloon took the transmitter/antenna system higher?
Daniel
"By including the loading coil in a metal box that is part of the transmitter assembly, such as is done in the LPB AM-2000 and the Rangemaster AM-1000, such an objection is prevented. The FCC has apparently not ruled on this subject."
I *think* the Rangemaster's box is fiberglass (1/4" thick, made in Germany?), though my memory could be mistaken on that point.
However, mounting the loading coil in a metal box with the transmitter could have some advantages over an exposed coil. First one I can think of is rain. Some may live in more arid climates, but at least some of us live where there is a considerable amount of precipitation. I'm not certain, but I would think that water trickling down the coil or dampness on the coil could affect the tuning of the antenna since water doesn't have the same dielectric coefficient as air there is some capacitance between turns? I know that with CB (11 meter) operation, water getting into an antenna's loading coil generally drastically affects the swr until it dries back out. Even when it is not actively raining, I would think that dampness between and under the wires of a coil wound on something like PVC (for example) would have an affect on the tuning, and in damp weather could take days or weeks to dry out fully.
Another consideration would be security. A coil inside a box would be better protected from vandalism and etc.
Also it *might* make tuning easier by eliminating some of the hand/body capacitance at least in the region of the loading coil.
As to it being acually necessary/desirable from the FCC POV? Perhaps, I can't say for certain. But considering the Rangemaster has it's loading coil inside the same non-metal box as the transmitter and was certified, and considering that I do not recall any FCC field actions which mention the presence of a loading coil as grounds for a NOUO/NAL/Citation, I'm not seeing the logic for it as a priority. As already mentioned, however, I can see other possible reasons where it could be perhaps advantageous.
Thank you for the explanation of natural groundplane. My next question regarding the natural groundplane is does it exist when there is no wired connection between the transmitter and the ground? If, for example, a battery operated transmitter and attached antenna is hung from a weather balloon or something so the lowest part is 10 ft from the ground, would the earth still act as a natural groundplane? Would there be a difference as the balloon took the transmitter/antenna system higher?
Daniel
While working on the Part 15 AM "Standard Antenna" model, Prof. Trainotti also calculated his results for larger Artificial Ground Plane diameters than the 3 meters he used in his previous report. I found this information to be almost as significant as his original report, which is in a previous post in this thread. This supplemental report shows whether or not it is worthwhile to expend a lot of effort and expense to construct a large metallic ground plane for Part 15. What follows is an edited version of Prof. Trainotti's supplemental report:
"This is the last of my data for the Part 15 monopole antenna I analyzed. These are the results for Artificial Ground Plane diameters of 6, 12, 20, and 40 meters. The values are for the three Q factors used previously, and for the three types of soil: Wet, Average, and Dry.
"Artificial Ground Plane diameter = 6 meters:
Wet soil, Rgp = 1.03 ohms
Average soil, Rgp = 1.57 ohms
Dry soil, Rgp = 4.96 ohms
"Q = 400
Wet soil, Pr = 368 uW, E = 1.82 mV/m
Average soil, Pr = 344 uW, E = 1.76 mV/m
Dry soil, Pr = 243 uW, E = 1.48 mV/m
"Q = 200
Wet soil, Pr = 200 uW, E = 1.34 mV/m
Average soil, Pr = 194 uW, E = 1.32 mV/m
Dry soil, Pr = 157 uW, E = 1.19 mV/m
"Q = 100
Wet soil, Pr = 105 uW, E = 0.97 mV/m
Average soil, Pr = 102 uW, E = 0.96 mV/m
Dry soil, Pr = 92 uW, E = 0.91 mV/m
"Artificial Ground Plane diameter = 12 meters
Wet soil, Rgp = 0.446 ohms
Average soil, Rpg = 0.576 ohms
Dry soil, Rgp = 1.83 ohms
"Q = 400
Wet soil, Pr = 397 uW, E = 1.89 mV/m
Average soil, Pr = 389 uW, E = 1.87 mV/m
Dry soil, Pr = 333 uW, E = 1.83 mV/m
"Q = 200
Wet soil, Pr = 209 uW, E = 1.34 mV/m
Average soil, 206 uW, E = 1.36 mV/m
Dry soil, 191 uW, , E = 1.31 mV/m
"Q = 100
Wet soil, Pr = 107 uW, E = 0.98 mV/m
Average soil, Pr = 107 uW, E = 0.98 mV/m
Dry soil, Pr = 102 uW, E = 0.96 mV/m
"Artificial Ground Plane diameter = 20 meters
Wet soil, Rgp = 0.166 ohms
Average soil, Rgp = 0.276 ohms
Dry soil, Rgp = 0.876 ohms
"Q = 400
Wet soil, Pr = 414 uW, E = 1.93 mV/m
Average soil, Pr = 405 uW, E = 1.91 mV/m
Dry soil, Pr = 376 uW, E = 1.84 mV/m
"Q = 200
Wet soil, Pr = 215 uW, E = 1.39 mV/m
Average soil, Pr = 212 uW, E = 1.38 mV/m
Dry soil, Pr = 203 uW, E = 1.35 mV/m
"Q = 100
Wet soil, Pr = 109 uW, E = 0.99 mV/m
Average soil, Pr = 107 uW, E = 0.98 mV/m
Dry soil, Pr = 105 uW, E = 0.97 mV/m
"Artificial Ground Plane diameter = 40 meters
Wet soil, Rgp = 0.076 ohms
Average soil, Rgp = 0.126 ohms
Dry soil, Rgp = 0.406 ohms
"Q = 400
Wet soil, Pr = 418 uW, E = 1.94 mV/m
Average soil, Pr = 414 uW, E = 1.93 mV/m
Dry soil, Pr = 401 uW, E = 1.90 mV/m
"Q = 200
Wet soil, Pr = 215 uW , E = 1.39 mV/m
Average soil, Pr = 215 uW, E = 1.39 mV/m
Dry soil, Pr = 209 uW, E = 1.37 mV/m
"Q = 100
Wet soil, Pr = 109 uW, E = 0.99 mV/m
Average soil, Pr = 109 uW, E = 0.99 mV/m
Dry soil, Pr = 107 uW, E = 0.98 mV/m
" A ground plane resistance decrease occurs when the metal artificial ground plane diameter is increased. Nevertheless, the tuning coil resistance dominates, making the ground plane resistance relatively unimportant. This means that the tuning coil resistance is the most important in determining the input resistance of the antenna. It is not important for the metallic artificial ground plane to be more than 6 meters in diameter."
While working on the Part 15 AM "Standard Antenna" model, Prof. Trainotti also calculated his results for larger Artificial Ground Plane diameters than the 3 meters he used in his previous report. I found this information to be almost as significant as his original report, which is in a previous post in this thread. This supplemental report shows whether or not it is worthwhile to expend a lot of effort and expense to construct a large metallic ground plane for Part 15. What follows is an edited version of Prof. Trainotti's supplemental report:
"This is the last of my data for the Part 15 monopole antenna I analyzed. These are the results for Artificial Ground Plane diameters of 6, 12, 20, and 40 meters. The values are for the three Q factors used previously, and for the three types of soil: Wet, Average, and Dry.
"Artificial Ground Plane diameter = 6 meters:
Wet soil, Rgp = 1.03 ohms
Average soil, Rgp = 1.57 ohms
Dry soil, Rgp = 4.96 ohms
"Q = 400
Wet soil, Pr = 368 uW, E = 1.82 mV/m
Average soil, Pr = 344 uW, E = 1.76 mV/m
Dry soil, Pr = 243 uW, E = 1.48 mV/m
"Q = 200
Wet soil, Pr = 200 uW, E = 1.34 mV/m
Average soil, Pr = 194 uW, E = 1.32 mV/m
Dry soil, Pr = 157 uW, E = 1.19 mV/m
"Q = 100
Wet soil, Pr = 105 uW, E = 0.97 mV/m
Average soil, Pr = 102 uW, E = 0.96 mV/m
Dry soil, Pr = 92 uW, E = 0.91 mV/m
"Artificial Ground Plane diameter = 12 meters
Wet soil, Rgp = 0.446 ohms
Average soil, Rpg = 0.576 ohms
Dry soil, Rgp = 1.83 ohms
"Q = 400
Wet soil, Pr = 397 uW, E = 1.89 mV/m
Average soil, Pr = 389 uW, E = 1.87 mV/m
Dry soil, Pr = 333 uW, E = 1.83 mV/m
"Q = 200
Wet soil, Pr = 209 uW, E = 1.34 mV/m
Average soil, 206 uW, E = 1.36 mV/m
Dry soil, 191 uW, , E = 1.31 mV/m
"Q = 100
Wet soil, Pr = 107 uW, E = 0.98 mV/m
Average soil, Pr = 107 uW, E = 0.98 mV/m
Dry soil, Pr = 102 uW, E = 0.96 mV/m
"Artificial Ground Plane diameter = 20 meters
Wet soil, Rgp = 0.166 ohms
Average soil, Rgp = 0.276 ohms
Dry soil, Rgp = 0.876 ohms
"Q = 400
Wet soil, Pr = 414 uW, E = 1.93 mV/m
Average soil, Pr = 405 uW, E = 1.91 mV/m
Dry soil, Pr = 376 uW, E = 1.84 mV/m
"Q = 200
Wet soil, Pr = 215 uW, E = 1.39 mV/m
Average soil, Pr = 212 uW, E = 1.38 mV/m
Dry soil, Pr = 203 uW, E = 1.35 mV/m
"Q = 100
Wet soil, Pr = 109 uW, E = 0.99 mV/m
Average soil, Pr = 107 uW, E = 0.98 mV/m
Dry soil, Pr = 105 uW, E = 0.97 mV/m
"Artificial Ground Plane diameter = 40 meters
Wet soil, Rgp = 0.076 ohms
Average soil, Rgp = 0.126 ohms
Dry soil, Rgp = 0.406 ohms
"Q = 400
Wet soil, Pr = 418 uW, E = 1.94 mV/m
Average soil, Pr = 414 uW, E = 1.93 mV/m
Dry soil, Pr = 401 uW, E = 1.90 mV/m
"Q = 200
Wet soil, Pr = 215 uW , E = 1.39 mV/m
Average soil, Pr = 215 uW, E = 1.39 mV/m
Dry soil, Pr = 209 uW, E = 1.37 mV/m
"Q = 100
Wet soil, Pr = 109 uW, E = 0.99 mV/m
Average soil, Pr = 109 uW, E = 0.99 mV/m
Dry soil, Pr = 107 uW, E = 0.98 mV/m
" A ground plane resistance decrease occurs when the metal artificial ground plane diameter is increased. Nevertheless, the tuning coil resistance dominates, making the ground plane resistance relatively unimportant. This means that the tuning coil resistance is the most important in determining the input resistance of the antenna. It is not important for the metallic artificial ground plane to be more than 6 meters in diameter."
Rattan,
You're right, of course, about the Rangemaster box. Sorry about that. The fact that the loading coil is in the transmitter box, however, still should cause its wire not to be considered to be part of the antenna length.
The ground enhances the gain of an antenna, such as a short vertical dipole, if it is close to ground because of ground reflection. A remote vertical dipole will not be affected much by the ground. The return path of displacement current for a dipole remote from earth is through the air (or space), and not through ground.