Range Limit for Legal Part 15 AM

[rfry]

There have been posts here and elsewhere reporting unexpectedly great coverage distances by certain "Part 15" AM systems.

Below is a calculation representing about the greatest consistent range that can be expected from a legal Part 15 AM system, over terrain with the highest ground conductivity shown in the FCC'S M-3 chart for the continental US.

The field strength values are referenced to the FCC's MW propagation curves for this frequency and ground conductivity.

These numbers should help separate the claims of exceptional coverage by a legal Part 15 system from practical reality.

DATA:
Frequency = 1600 kHz
Applied Power = 80 mW
Radiator = 3-meter resonant vertical with base at ground level
Coil Resistance = 2 ohms
R-F Ground Resistance = 10 ohms
Ground Conductivity = 30.0 mS/m
Radiation at 1 mile = 0.2 mV/m

RESULTS:

Contour level > Distance to contour

5.000 mV/m > 0.0340 miles (good signal to cheap, indoor radio)

2.000 mV/m > 0.0850 miles (acceptable, but somewhat noisy signal to cheap indoor radio)

0.100 mV/m > 1.5865 miles (acceptable, but noisy signal to a good car radio in an area with no overhead wires, no local electrical interference, and no co-channel interference)

//

 

[SUPERCASTER]

There have been posts here and elsewhere reporting unexpectedly great coverage distances by certain "Part 15" AM systems.

Below is a calculation representing about the greatest consistent range that can be expected from a legal Part 15 AM system, over terrain with the highest ground conductivity shown in the FCC'S M-3 chart for the continental US.

The field strength values are referenced to the FCC's MW propagation curves for this frequency and ground conductivity.

These numbers should help separate the claims of exceptional coverage by a legal Part 15 system from practical reality.

DATA:
Frequency = 1600 kHz
Applied Power = 80 mW
Radiator = 3-meter resonant vertical with base at ground level
Coil Resistance = 2 ohms
R-F Ground Resistance = 10 ohms
Ground Conductivity = 30.0 mS/m
Radiation at 1 mile = 0.2 mV/m

RESULTS:

Contour level > Distance to contour

5.000 mV/m > 0.0340 miles (good signal to cheap, indoor radio)

2.000 mV/m > 0.0850 miles (acceptable, but somewhat noisy signal to cheap indoor radio)

0.100 mV/m > 1.5865 miles (acceptable, but noisy signal to a good car radio in an area with no overhead wires, no local electrical interference, and no co-channel interference)

//

I disagree with your assumptions.

 

[rfry]

I disagree with your assumptions.

If you could specify which assumptions you disagree with, and explain your basis for disagreeing with them -- I will have another look. Thanks.
//

 

[SUPERCASTER]

There have been posts here and elsewhere reporting unexpectedly great coverage distances by certain "Part 15" AM systems.

Below is a calculation representing about the greatest consistent range that can be expected from a legal Part 15 AM system, over terrain with the highest ground conductivity shown in the FCC'S M-3 chart for the continental US.

The field strength values are referenced to the FCC's MW propagation curves for this frequency and ground conductivity.

These numbers should help separate the claims of exceptional coverage by a legal Part 15 system from practical reality.

DATA:
Frequency = 1600 kHz
Applied Power = 80 mW
Radiator = 3-meter resonant vertical with base at ground level
Coil Resistance = 2 ohms
R-F Ground Resistance = 10 ohms
Ground Conductivity = 30.0 mS/m
Radiation at 1 mile = 0.2 mV/m

RESULTS:

Contour level > Distance to contour

5.000 mV/m > 0.0340 miles (good signal to cheap, indoor radio)

2.000 mV/m > 0.0850 miles (acceptable, but somewhat noisy signal to cheap indoor radio)

0.100 mV/m > 1.5865 miles (acceptable, but noisy signal to a good car radio in an area with no overhead wires, no local electrical interference, and no co-channel interference)

//

I disagree with your assumptions.

I disagree with your assumptions.

If you could specify which assumptions you disagree with, and explain your basis for disagreeing with them -- I will have another look. Thanks.
//

The brief, simple answer is:
The absolute radiation limits you claim (see above) for the medium wave AM band is neither expressed nor implied in the FCC's part 15 rules. I think it is best that way, and I believe most other part 15 users would agree. A little latitude helps a lot.
There is such a revised limit for the FM band and it has almost killed experimentation, community broadcasting, and the usefullness of part 15 broadcasting on FM. Is that your intention for AM also?
If not, then why imagineer, propose and publish new, more restrictive, limits for AM, handcuffing innovation, experimentation, and community broadcasting!
Why not let sleeping dogs lie, and users enjoy their part 15 AM transmitters, as they are?
Most are doing no harm, and some provide valuable community service.
The change in the FM part 15 rules and limits and strict enforcement has resulted in many FM part 15 stations closing down or being forced to do so. Most were not really creating any interference, or they would, and could have been shut down under the old FM rules.
If serious interference on AM is created, I'm sure the FCC will handle the situation accordingly, without any help.
No personal criticism is intended.
For Better Broadcasting,
SUPERCASTER

 

[rfry]

There is such a revised limit for the FM band and it has almost killed experimentation, community broadcasting, and the usefullness of part 15 broadcasting on FM. Is that your intention for AM also? If not, then why imagineer, propose and publish new, more restrictive, limits for AM, handcuffing innovation, experimentation, and community broadcasting! Why not let sleeping dogs lie, and users enjoy their part 15 AM transmitters, as they are?

Thanks for your comments. Truthfully I have no wish to limit those wanting to experiment with Part 15 AM systems. My only purpose here was to show what kind of range could be expected according the conditions I posted, using a logical approach.

People are always free to operate however they wish. My post just gives them a reference point to use, if they wish to.
//

 

[ironbear]

It's a rare situation where experimental approaches appear to be OK under the rules, which don't limit the transmitter/antenna to ground level mounting. R. Fry's data is extremely useful, as always.

 

[SUPERCASTER]

Most part 15 AM transmitters are not ground level mounted, nor are they likely to be, and there is no such requirement in the part 15 rules.
However, there is a provision for making up to 5 home built part 15 AM transmitters limited to 100 milliwatts final stage input power.
R.Fry's coverage calculations are based solely on his unique interpretation of the FCC's AM part 15 rules, and the errors are compunded by unwarrented technical assumptions and incorrect data.

 

[rfry]

R.Fry's coverage calculations are based solely on his unique interpretation of the FCC's AM part 15 rules, and the errors are compunded by unwarrented technical assumptions and incorrect data.

My numbers were based on:

-- a known legal Part 15 AM antenna configuration per 15.219
-- a high-typical tx output power based on 100 mW DC input at 80% PA efficiency
-- a radiation efficiency based on very low values of coil and r-f ground resistance for these systems
-- the highest ground conductivity in the US per the FCC M-3 chart
-- the FCC's propagation curves for the frequency and conductivity

So these assumptions define a very good Part 15 AM system, probably better than most real installations of this configuration. The analysis has not been contrived to show poor performance -- actually, the opposite.

What exactly do you consider to be the unwarranted assumptions and incorrect data in this approach, Supercaster? If you want to see it, I can increase the coil and r-f ground loss, and use poorer ground conductivity that would be more typical of the average installation. But that will reduce the coverage distances below those you apparently think are too low, already. Please advise? Thanks.
//

 

[SUPERCASTER]

R.Fry's coverage calculations are based solely on his unique interpretation of the FCC's AM part 15 rules, and the errors are compunded by unwarrented technical assumptions and incorrect data.

My numbers were based on:

-- a known legal Part 15 AM antenna configuration per 15.219

A-There are many legal and approved possible antenna configurations and installation possibilities that are legal under part 15. The regulation was written to be flexible to cover various uses and situations. Which one, approved under which of the several legal part 15 approval methods, and why is this the only or best one? Elevated (and by how much) or ground level, and why?
Why is your choice of antenna, and interpretation of part 15 rules, superior to all other approved configurations, and FCC inspectors findings. Does your interpretation truly describe a maximum allowable radiation limit when higher limits have been FCC approved?

-- a high-typical tx output power based on 100 mW DC input at 80% PA efficiency

A-Typical does not mean only, or maximum!
You have not taken into account multiple transmitters, co-located, synchronized or non-syncronized at all phase differences or at various distances (as allowed by part 15) and the effects.

-- a radiation efficiency based on very low values of coil and r-f ground resistance for these systems

A-There are huge variations in possible, legal and approved (under various sections of part 15) ground systems, resulting in large differences in signal propagation.

-- the highest ground conductivity in the US per the FCC M-3 chart

A-Suppose the radials are in or near seawater. That has MUCH higher conductivity then you indicate. So might steel reinforced concrete, or a copper roof, macadam or many other materials and situations.

-- the FCC's propagation curves for the frequency and conductivity

So these assumptions define a very good Part 15 AM system, probably better than most real installations of this configuration. The analysis has not been contrived to show poor performance -- actually, the opposite.

A-Since the part 15 rules allow several methods of compliance for medium wave AM band transmission systems, your assumptions remain just that. Assumptions can not form a sound basis for claiming an absolute maximum limit.

What exactly do you consider to be the unwarranted assumptions and incorrect data in this approach, Supercaster? If you want to see it, I can increase the coil and r-f ground loss, and use poorer ground conductivity that would be more typical of the average installation. But that will reduce the coverage distances below those you apparently think are too low, already. Please advise? Thanks.

A-Irrelevent. Your coil and antenna designs are only yours. Someone else would probably come up with another design. Weather and the effects of local incidental radiators are only 2 of several factors that greatly effect short antennas (in relation to wavelength). These effects are very pronounced at medium wave frequencies, and are much less at higher frequencies.
Additionally, local conditions, antenna placement mounting methods and a number of other factors can cause more antenna gain or loss both vertically and horizontally. An almost unlimited number of antenna patterns can be produced and often are.
Had the FCC intended such a radiation limit for all medium wave devices they would have clearly included it in the part 15 rules, as they have done in thir most recent FM frequency revision.
//

Professional medum wave propagation software, and actual field measurements, produce provable, measureable results far different from your assumptions and methods. When professional calculations are made, rarely do they result in an exactly omnidirectional pattern as your results imply.

Overall your methods are seriously incomplete, flawed, and based on your assumptions, fancy, oversimplifications, and interpretations.
The results you are publishing are hypothetical and inacurate.

 

[rfry]

I'll respond to a few of your comments below.

There are many legal and approved possible antenna configurations and installation possibilities that are legal under part 15. Which one, approved under which of the several legal part 15 approval methods, and why is this the only or best one? etc

The antenna was described in my original post, but repeating it here: "Radiator = 3-meter resonant vertical with base at ground level." Part 15.219 is the only place in the Rules that defines the antenna; there are not several of them. I put the base of the 3-meter radiating structure (at the bottom of the ground lead) at ground level because that ensures that the radiator does not exceed the 3-meter length defined in 15.219.

If this whole system was installed on a rooftop, flagpole, tower, billboard etc with a long conductor from the tx chassis to a buried r-f ground, then the radiating length of the antenna no longer is 3 meters. This is a fact of physics that cannot be denied -- no matter how many Part 15 AM systems operate that way, and how many them "passed FCC inspection."

You have not taken into account multiple transmitters, co-located, synchronized or non-syncronized at all phase differences or at various distances (as allowed by part 15) and the effects.

Correct. My numbers were based on a simple, more typical installation whose performance should have the widest interest.

A-There are huge variations in possible, legal and approved (under various sections of part 15) ground systems, resulting in large differences in signal propagation.

As I posted earlier, low losses in the coil and r-f ground were used to show what this system could do under nearly the best conditions. Of course, higher losses will reduce performance. But the goal was to evaluate a very good system, not a poor one.

Suppose the radials are in or near seawater. That has MUCH higher conductivity then you indicate. So might steel reinforced concrete, or a copper roof, macadam or many other materials and situations.

The field strength produced by a MW antenna (even a Part 15 system) depends on the conductivity along the entire path between the transmit and receive antennas -- not just on the performance of the r-f ground system of the tx antenna. The r-f ground loss at the Part 15 AM tx antenna determines in large part how much of the available tx power is radiated. Ground conductivity beyond the limits of that r-f ground system then determine how much loss that radiation encounters as it propagates to the rx antenna.

If the radials were installed in/under seawater, that would increase the amount of the available power that the Part 15 system radiated. But as soon as that radiation encounters "dry land," it is subject to the same propagation losses as from any other installation. Again, I chose a very high ground conductivity to show nearly a best-case condition for an overland path.

Professional medum wave propagation software, and actual field measurements, produce provable, measureable results far different from your assumptions and methods.

The distances I posted are calculated from the FCC's MW propagation curves, as I've stated. Professional level software was used. The FCC curves are based on measured data, and have been proven accurate for licensed AM broadcast allocations and interference predictions for many decades. Please publish your methods and results showing a different conclusion for the conditions I used.

Overall your methods are seriously incomplete, flawed, and based on your assumptions, fancy, oversimplifications, and interpretations. The results you are publishing are hypothetical and inacurate.

Certainly you are entitled to your opinion. I'll leave it to others to decide which of us has presented the more valid data and commentary.
//

 

[SUPERCASTER]

I'll respond to a few of your comments below.

There are many legal and approved possible antenna configurations and installation possibilities that are legal under part 15. Which one, approved under which of the several legal part 15 approval methods, and why is this the only or best one? etc

The antenna was described in my original post, but repeating it here: "Radiator = 3-meter resonant vertical with base at ground level." Part 15.219 is the only place in the Rules that defines the antenna; there are not several of them. I put the base of the 3-meter radiating structure (at the bottom of the ground lead) at ground level because that ensures that the radiator does not exceed the 3-meter length defined in 15.219.

A-This is your unique interpretation of the part 15 antenna rules, not the generally accepted, utilized, approved, antenna mounting method. It is rare to find a part 15 antenna mounted directly on the earth, nor is such mounting required (as you claim). Inspected and FCC approved antennas for part 15 can take many configurations depending on the installation, and are not exclusively required to be directly mounted at ground level.

If this whole system was installed on a rooftop, flagpole, tower, billboard etc with a long conductor from the tx chassis to a buried r-f ground, then the radiating length of the antenna no longer is 3 meters. This is a fact of physics that cannot be denied -- no matter how many Part 15 AM systems operate that way, and how many them "passed FCC inspection."

A-Speculation, misinterpretation, and misdirected assumptions. Your statement has nothing to do with the facts of physics, but it does depend on your unique interpretation of the words "ground lead" for mass produced, manufactured, certified transmitters. Part 15 stations can also be verified or even totally home built, rather then certified. Your assumptions do not apply to these installations, nor are manufactured, certified transmitters required or even expected to have their antennas ground mounted.

You have not taken into account multiple transmitters, co-located, synchronized or non-syncronized at all phase differences or at various distances (as allowed by part 15) and the effects.

Correct. My numbers were based on a simple, more typical installation whose performance should have the widest interest.

A-There are huge variations in possible, legal and approved (under various sections of part 15) ground systems, resulting in large differences in signal propagation.

As I posted earlier, low losses in the coil and r-f ground were used to show what this system could do under nearly the best conditions. Of course, higher losses will reduce performance. But the goal was to evaluate a very good system, not a poor one.

Suppose the radials are in or near seawater. That has MUCH higher conductivity then you indicate. So might steel reinforced concrete, or a copper roof, macadam or many other materials and situations.

The field strength produced by a MW antenna (even a Part 15 system) depends on the conductivity along the entire path between the transmit and receive antennas -- not just on the performance of the r-f ground system of the tx antenna. The r-f ground loss at the Part 15 AM tx antenna determines in large part how much of the available tx power is radiated. Ground conductivity beyond the limits of that r-f ground system then determine how much loss that radiation encounters as it propagates to the rx antenna.

If the radials were installed in/under seawater, that would increase the amount of the available power that the Part 15 system radiated. But as soon as that radiation encounters "dry land," it is subject to the same propagation losses as from any other installation. Again, I chose a very high ground conductivity to show nearly a best-case condition for an overland path.

Professional medum wave propagation software, and actual field measurements, produce provable, measureable results far different from your assumptions and methods.

The distances I posted are calculated from the FCC's MW propagation curves, as I've stated. Professional level software was used. The FCC curves are based on measured data, and have been proven accurate for licensed AM broadcast allocations and interference predictions for many decades. Please publish your methods and results showing a different conclusion for the conditions I used.

A-The FCC MW propagation curves show conductivity averaged over miles, not (as you claim) very local soil or conductivity variations and conditions. You also claim part 15 stations can not legally cover miles, therefore the curves are only accurate, and only can be applied to, the higher powered, large coverage broadcast stations for which the charts (averaged over miles) were made, and designed to be used.
By way of example, it is not unusual for a part 15 transmitter to be used to cover a paved parking lot (perhaps a drive-in theatre) from the middle, to provide parking or other entertainment or information. The parking lot could be made of blacktop, steel reinforced concrete, or other material. Since the part 15 coverage would be primarily over the area of the parking lot, A MW conductivity chart for various types of paving is required. Do you have such a detailed FCC MW chart?

Overall your methods are seriously incomplete, flawed, and based on your assumptions, fancy, oversimplifications, and interpretations. The results you are publishing are hypothetical and inacurate.

Certainly you are entitled to your opinion. I'll leave it to others to decide which of us has presented the more valid data and commentary.
//

If you restated your coverage claims for your field intensity calculations to "Typical coverage for a part 15 station with 3 meter antenna directly on the ground", rather then "M

 

[SUPERCASTER]

Here is the end of my posting which I was not able to complete due to this board's time limit.

If you restated your coverage claims for your field intensity calculations to "Typical coverage for a part 15 station with 3 meter antenna directly mounted on the ground", rather then "Range Limit for Legal Part 15 AM", I would be more inclined to support your calculations.
Your methods and assumptions can not be used to support your "Range Limit" statement.
Ground waves and not direct waves, or sky waves are the principal method of transmission at long wave and medium wave broadcast frequencies. Ground waves are usually ignored at short wave frequencies and above because of their limited propagation range at higher frequencies.
Here is a link to professional medium wave coverage software:
http://www.v-soft.com/AM/index.htm
Your 2mv/m primary coverage only extends to 0.0850 miles or approximately 450 feet. Less then a half wavelength at most broadcast frequencies. Therefore local ground conditions and inductive wave near field propagation, rather then the usual far field calculation method would be necessary for accuracy.

 

[rfry]

Your 2mv/m primary coverage only extends to 0.0850 miles or approximately 450 feet. Less then a half wavelength at most broadcast frequencies. Therefore local ground conditions and inductive wave near field propagation, rather then the usual far field calculation method would be necessary for accuracy.

Antenna engineering textbooks state that the far field begins at a radius of 2*L2/lambda, where L is the maximum dimension of the antenna in meters, and lambda is the wavelength in meters. So a distance of 450 feet (137 meters) is well into the far field of a 3-meter radiator on 1,600 kHz.

Your statement has nothing to do with the facts of physics, but it does depend on your unique interpretation of the words "ground lead" for mass produced, manufactured, certified transmitters.

Sorry, but your belief is simply incorrect that the entire conducting path from the ground terminal of an elevated Part 15 AM tx to the point where that path enters the physical earth is not a radiating part of the antenna. If you want to investigate this, download a free demo version of NEC-2, and model it for yourself. Or if you have access to such an elevated Part 15 AM installation, just remove the ground connection from it at the tx chassis or at the junction of the short "ground lead" and the "massive ground wire," and note the effect on distant field strength of doing that.
//

 

[rfry]

Here is a response to another issue in an earlier post by SUPERCASTER.

The FCC MW propagation curves show conductivity averaged over miles, not (as you claim) very local soil or conductivity variations and conditions.

The affect of ground conductivity on field strength is small over a short propagation path from a MW radiator, no matter what the actual value of that ground conductivity. This was proven by empirical measurements made by Brown, Lewis & Epstein of RCA Labs in their 1937 paper published in The Proceedings of the IRE. These measurements showed that the fields radiated by a 1/4-wave monopole radiator with an excellent ground system were within 2% of the theoretical maximum inverse distance field for the power radiated, over a 3/10 mile path. In other words, the affect of ground conductivity was negligible over this short path.

My calculated field strength at a distance of ~450 feet from my Part 15 system was 2 mV/m. The theoretical inverse distance field at 450 feet from my radiation source is 2.05 mV/m, so my calculations stand up well to the BL&E paper -- which paper was used by the FCC to establish the minimum radiation efficiencies for the antennas used by the various classes of licensed AM broadcast stations.

By way of example, it is not unusual for a part 15 transmitter to be used to cover a paved parking lot (perhaps a drive-in theatre) from the middle, to provide parking or other entertainment or information. The parking lot could be made of blacktop, steel reinforced concrete, or other material. Since the part 15 coverage would be primarily over the area of the parking lot, A MW conductivity chart for various types of paving is required. Do you have such a detailed FCC MW chart?

No such detailed charts exist, nor are they necessary to adequately analyze the performance of a Part 15 AM system over short paths. This was addressed in my comments above.
//

 

[SUPERCASTER]

Please note the statement at the top of page 2 "Antenna modeling in this band is quite unlike that in other bands........"
That is why the government developed this specialized software.
That calls into question the accuracy of NEC 2 and other similar general purpose all band software for use at these frequencies.
Link:
http://www.its.bldrdoc.gov/programs/its_e/low_med_freq_ground_sky_wave/low_med_freq_ground_sky_wave_blue.pdf

The formula you quote is for "short reactive near field non-radiating conductors."

I have 2 different model FCC certified Part 15 AM transmitters now in front of me. Both have external ground connections that instructions indicate are for connection to additional external above ground conductors. Neither have provisions for or any mention of the grounding limitations nor ground mounted antennas you claim are necessary for FCC compliance.

At least three current manufacturers of FCC certified part 15 transmitters differ with your "maximum" field strength calculations, antenna models, grounding models or part 15 antenna and field strength limitations. All have suggested antenna implementations that differ with your assumptions, and intrepretations of the FCC rules.

The FCC certifies and verifies many part 15 RF systems that do not comply with your interpretation of THEIR rules.

Regarding your claims that earth grounds do not radiate, this is untrue, especially at medium and long wavelengths, as myriad of applications and FCC approved installations prove.

 

[rfry]

"Antenna modeling in this band is quite unlike that in other bands........" That is why the government developed this specialized software. That calls into question the accuracy of NEC 2 and other similar general purpose all band software for use at these frequencies.

NEC was developed in 1981 by Lawrence-Livermore Laboratories under contract to the US Navy, and its accuracy has been well-proven for use at MW frequencies. Note that NEC it its various forms is now, and has for years been used by broadcast consulting firms to design MW antenna systems, including directional arrays. The results of these NEC calculations are accepted by the FCC for this purpose.

The formula you quote is for "short reactive near field non-radiating conductors."

Section 2.2.4 of the college textbook "Antenna Theory Analysis and Design" by Balanis (2nd Edition, 1997) says this about the reactive near-field region of an antenna, "For a very short dipole, or equivalent radiator, the outer boundary {of the reactive near-field - Ed.} is commonly taken to exist at a distance of Lambda/2 *pi from the antenna surface." For the electrically very short radiator used on Part 15 AM, this distance for an operating frequency of 1,600 kHz occurs at about 98 feet. This is not the equation I posted earlier for the far-field radius, nor does that equation apply to the reactive near-field radius.

I have 2 different model FCC certified Part 15 AM transmitters now in front of me. Both have external ground connections that instructions indicate are for connection to additional external above ground conductors. Neither have provisions for or any mention of the grounding limitations nor ground mounted antennas you claim are necessary for FCC compliance. At least three current manufacturers of FCC certified part 15 transmitters differ with your "maximum" field strength calculations, antenna models, grounding models or part 15 antenna and field strength limitations. All have suggested antenna implementations that differ with your assumptions, and intrepretations of the FCC rules.

The transmitters may have been Part 15 certified, but under what conditions? Do the manufacturer's installation suggestions and drawings say that these elevated configurations with short "ground leads" and long, "massive ground wires" are those in which the transmitter was certified, and therefore will meet 15.219 -- or is that just most people's assumption?

Meeting 15.219 ultimately is a user responsibility. If the certified transmitter is not used in the configuration in which it was certified (including the specific antenna configuration), then the certification no longer applies, and users are on their own.

The FCC certifies and verifies many part 15 RF systems that do not comply with your interpretation of THEIR rules.

Are you meaning the measurements that are taken by/for a tx manufacturer in the process of applying for Part 15 AM equipment certification, or that some elevated installations using long, radiating grounds reportedly have not been "written up" by FCC field inspectors?

The FCC has the discretion to treat its Rules as it wishes. That may not necessarily mean that systems they inspect always meet the Rules in a pure engineering sense. It may also mean that the field inspectors don't have the specific antenna engineering background needed to fully understand the radiating characteristics of the systems they are inspecting.

Regarding your claims that earth grounds do not radiate, this is untrue, especially at medium and long wavelengths, as myriad of applications and FCC approved installations prove.

Any r-f ground buried in the earth and used with a MW vertical radiator does not by itself produce any useful radiation. It DOES improve the radiation possible from the vertical radiator above the earth, by reducing ground losses -- which losses are in series with the antenna current. Please check with Terman, Kraus, Balanis or numerous other antenna engineering authors to verify this.
//

 

[dbdigital]

Seems to me that either on this board or another, some creative person suggested the idea of attaching several transmitters to one antenna for greater output. I'm fairly sure the TXs would have to be synchronized somehow; but does anyone recall what the verdict was on that idea?

The feasability and legality of it? Just curious.

db

 

[pianoplayer88key]

Seems to me that either on this board or another, some creative person suggested the idea of attaching several transmitters to one antenna for greater output. I'm fairly sure the TXs would have to be synchronized somehow; but does anyone recall what the verdict was on that idea?

The feasability and legality of it? Just curious.

db

I've read somewhere in the FCC rules that you can build 5 homebrew transmitters... I was wondering if you could stack 5 transmitters and antennas, each one being 100 milliwatts and 3 meters, for an effective equivalent of 500 milliwatts and 15 meters?

like this diagram's example:



ok, how do you embed an image? It's 539x563 pixels, 15k.

And, what about the idea of stacking multiple antennas end to end so they act as one larger antenna?

 

[rfry]

I've read somewhere in the FCC rules that you can build 5 homebrew transmitters... I was wondering if you could stack 5 transmitters and antennas, each one being 100 milliwatts and 3 meters, for an effective equivalent of 500 milliwatts and 15 meters? And, what about the idea of stacking multiple antennas end to end so they act as one larger antenna?

There would be a lot technical issues there. For example, even if the carriers of all txs were phase-locked, and their modulation was matched in time and polarity, there would need to be a way of isolating the r-f output stage of each tx from the others in the system. Otherwise some of each tx's power would appear at the other txs, instead of being radiated by the antenna(s). That is a complex problem to solve.

And most likely there would be FCC isssues, even if the engineering was done right.
//

 

[SUPERCASTER]

Seems to me that either on this board or another, some creative person suggested the idea of attaching several transmitters to one antenna for greater output. I'm fairly sure the TXs would have to be synchronized somehow; but does anyone recall what the verdict was on that idea?

The feasability and legality of it? Just curious.

db

I've read somewhere in the FCC rules that you can build 5 homebrew transmitters... I was wondering if you could stack 5 transmitters and antennas, each one being 100 milliwatts and 3 meters, for an effective equivalent of 500 milliwatts and 15 meters?

like this diagram's example:



ok, how do you embed an image? It's 539x563 pixels, 15k.

And, what about the idea of stacking multiple antennas end to end so they act as one larger antenna?

Stacked, syncronized, part 15 transmitters work even better when the transmitters are mounted at the top of each antenna, and none is mounted at ground level.