Part 15.219(b) rule

[Neil E.]

Whats more in testing this design I found either no, or extremely very low radiation coming from the mast pipe. The radiation is entirely coming from the copper pipe antenna....in all my installations.

Carl,

I am very interested in your measurement technique which lead to the conclusion quoted above. How do you separate the ground radiation from the antenna radiation? It seems to me that the way to do this is to measure the system field strength at a distance with and without the ground attached or with different length grounds, or to measure the RF current in the antenna and the ground and infer from this and the respective lengths the radiation. Is this what you did?

Depending on your instrumentation you might have been measuring the RF voltage to ground which can only relate to radiation when applied across a resistance (ohms in a wire or radiation resistance) since it is the current in an antenna system which produces radiation and not the voltage by itself. The voltage to ground will be higher measured from the antenna than it will be measured from the ground lead, yet the current (excepting the current in audio/power leads) will be the same in both elements. I speculate that your measurement methods were in error but you can correct me if I err.

Thanks,

Neil

 

[Neil E.]

What Rich is talking about is theoretical in nature, even conductors buried in the ground can radiate, and not be a pure RF ground, (though theoretically they are not supposed to radiate once buried) there is not necessarily a magic line at the dirt line if the quality of the ground in the area is very poor.

If radials are installed such that each fractional wavelength conductor has a "mate" at 180 degrees physically then the equal and opposite currents in these conductors will produce fields which cancel resulting in no net radiation.

I disagree with Rich that the RF impedance will vary greatly from the DC resistance of a conductor as a “pipe” for example. Rich can you show some calculations, for example a 10’ straight piece of #8 AWG wire would be about .00628 ohms DC, what would the impedance be at 1Mhz?

The self inductance of a length of wire and the skin effect both contribute to increasing the impedance of a conductor to RF over DC even at medium wave frequencies. These effects are not seen with DC, thus the AC resistance due to the skin effect is greater than the DC resistance, and the self inductance increases the reactance in addition to this further increasing the impedance. RF and DC measurements of resistance are not equivalent.

Neil

 

[SUPERCASTER]

Neil E. said:

If radials are installed such that each fractional wavelength conductor has a "mate" at 180 degrees physically then the equal and opposite currents in these conductors will produce fields which cancel resulting in no net radiation.

Untrue. The currents of all radials in a single vertical monopole antenna with ground radials or radial counterpoise are in phase and additive at the joined center point and not out of phase as you speculate.
You seem to be confusing physical compass orientation with electrical phase. Even though both compass direction and electrical phase are both measured in degrees, there is no direct relation between the two. All radials regardless of physical orientation in the ground plane are in phase and additive. Connect an RF (thermocouple) ammeter in series between a transmitter ground and the center point where the radials are joined. You will note that as additional radials are added the RF current increases, after about 90 or 120 radials the amount of increase starts to diminish for each additional radial, but still increases a bit. The compass baring of the radials do not matter, the return currents from all radials are still additive and all in phase.

 

[Neil E.]

I believe what I stated is correct.

You seem to be confusing physical compass orientation with electrical phase. Even though both compass direction and electrical phase are both measured in degrees, there is no direct relation between the two. All radials regardless of physical orientation in the ground plane are in phase and additive.

This is true for electrical phase, but the radiated fields also depend on the spatial (physical) phase so there is a direct relation between the electrical phase and the spatial phase. Since the radials have spatial phase differences the radiation will also have phase differences. The currents are electrically in phase viewed from the connection at the base of the antenna since here they all increase and decrease in phase and therefore add, but when viewed by an observer along a line perpendictular to the two radials which passes through the antenna base connections, the currents are 180 degrees out of phase since at an instant one current is going right and the other current is going left and they crash together in phase at your point of measurement where they are tied together at the antenna base. Since the fields radiate perpendicular to the radials, the observer in positioned to view the correct phase reference for the two conductors and the field phases as well. Therefore their fields radiated are also out of phase and cancel. Remember that an instantenous current viewed perpendicular to a wire as going right is 180 degrees out of phase with one from the same view going left in a parallel wire as is the case with twin lead transmission line in which the fields cancel and no radition is produced. The difference here is there is electrical phase shift and not spatial phase shift but the field effect is the same.

To keep it simple, let's just use two radials 180 physical degrees apart attached to the base. As the current collected by these radials to be returned to the antenna base add at the base they will be in electrical phase using this junction as the reference point, and the total will increase as you said. But the current in what let's call the north radial will be travelling south, and the current in the south radial will be travelling north, both into the test node at the antenna base where they add in phase. From an observer to the west, the currents will be 180 degrees out of phase since they are observed travelling equal and opposite directions and the generated radiated fields from each will also be equal and opposite and will cancel.

So, as you state correctly, at the collection point the currents are in phase and add, but as I say
due to the positions of the wires they are not in phase with respect to one another spatially and it is this spatial phase difference which causes the radiated fields to cancel. The field radiated from the north antenna by current going south produces an equal and opposite field to cancel that produced in the south antenna with the current going north. Since the currents are equal and opposite in direction in the radials the fields are also equal and opposite and cancel
.

The compass baring [sic] of the radials do not matter, the return currents from all radials are still additive and all in phase.

Yes they do. Consider two parallel radials inches apart. Since the current in each is going the same direction the radiated fields will be in phase and add. Compare this with the previous case where they are 180 degrees apart and the currents are going in opposite directions...the fields cancel though the currents are in phase where the radials are tied together to be returned to the transmitter. For a pair of radials not at 180 degrees, the field combination will be governed by a vector sine(theta) function which will not give cancellation at angles other than at 180 degrees and radiation lobes will result.

Neil

 

[rfry]

The compass baring of the radials do not matter, the return currents from all radials are still additive and all in phase.

Currents at the same relative locations along radials of equal lengths will have the same magnitude and phase. But the net, far-field radiation from every pair of radials physically opposite each other will cancel, as those currents always are traveling in opposite physical directions.

Below is a link to a NEC study illustrating this point, based on the currents and radiation from a "Tee" antenna.

http://i62.photobucket.com/albums/h85/rfry-100/TeeAntenna.gif

//

 

[SUPERCASTER]

A vertical monopole antenna over symmetrically oriented center connected field of radials (grounded or counterpoise) radiates equally (omnidirectionally) and in phase in all directions. Any phase difference would create a directional antenna. One side of the vertical antenna wire or tower that induces the current in the radials is exactly in phase with the other side, at the center point.

Since the fields radiate perpendicular to the radials, the observer in positioned to view the correct phase reference for the two conductors and the field phases as well. Therefore their fields radiated are also out of phase and cancel. Remember that an instantenous current viewed perpendicular to a wire as going right is 180 degrees out of phase with one from the same view going left in a parallel wire as is the case with twin lead transmission line in which the fields cancel and no radition is produced. The difference here is there is electrical phase shift and not spatial phase shift but the field effect is the same.

No.
The observer receives only the wave front headed toward him and not the radial wave front headed in other directions.

To keep it simple, let's just use two radials 180 physical degrees apart attached to the base. As the current collected by these radials to be returned to the antenna base add at the base they will be in electrical phase using this junction as the reference point, and the total will increase as you said. But the current in what let's call the north radial will be travelling south, and the current in the south radial will be travelling north, both into the test node at the antenna base where they add in phase. From an observer to the west, the currents will be 180 degrees out of phase since they are observed travelling equal and opposite directions and the generated radiated fields from each will also be equal and opposite and will cancel.

Again.
The observer receives only the wave front headed toward him and not the radial wave front headed in other directions.

The field radiated from the north antenna by current going south produces an equal and opposite field to cancel that produced in the south antenna with the current going north. Since the currents are equal and opposite in direction in the radials the fields are also equal and opposite and cancel

There are no North and South antennas, only one antenna. Remember this is a single omni-directional monopole antenna over a symmetrical field of radials. So there is no phase reversal or cancellation.
Again.
The observer receives only the wave front headed toward him and not the radial wave front headed in other directions.
Waves headed in other directions never reach the observer's radio, unless they bounce off something and return (multipath) or travel around the world.

Yes they do. Consider two parallel radials inches apart. Since the current in each is going the same direction the radiated fields will be in phase and add. Compare this with the previous case where they are 180 degrees apart and the currents are going in opposite directions...the fields cancel though the currents are in phase where the radials are tied together to be returned to the transmitter. For a pair of radials not at 180 degrees, the field combination will be governed by a vector sine(theta) function which will not give cancellation at angles other than at 180 degrees and radiation lobes will result.

Neil

Since this is an omni-directional vertical monopole and the observer's radio is only affected by the single wavefront heading toward him, he never gets the delayed wavefronts you mention that are headed in other directions. (They don't change direction and swerve around toward his radio).
If the cancellation effect you claim was actually the case then, indeed an omni-directional pattern from a single monopole over symmetrical ground radials would be impossible, and as you said multiple

radiation lobes will result.

The entire antenna system is in phase and omnidirectional when viewed from directly above the tower and radiates equally in all directions with none of the directional phase cancellation effects you claim. An observer on the plane of the radials only receives the wavefront headed toward him, and that is not affected by the wavefronts traveling in other directions, unless some object causes reflection of the wavefront propagating in other directions and redirects it toward the observer.
Remember:
The observer receives only the wave front headed toward him and not the radial wave front headed in other directions. They are headed elsewhere.
Waves headed in other directions never reach the observer's radio, unless they bounce off something and return (multipath) or travel around the world.

 

[SUPERCASTER]

The compass baring of the radials do not matter, the return currents from all radials are still additive and all in phase.

Currents at the same relative locations along radials of equal lengths will have the same magnitude and phase. But the net, far-field radiation from every pair of radials physically opposite each other will cancel, as those currents always are traveling in opposite physical directions.

Below is a link to a NEC study illustrating this point, based on the currents and radiation from a "Tee" antenna.

http://i62.photobucket.com/albums/h85/rfry-100/TeeAntenna.gif

//

We are discussing a single vertical monopole over symmetrical radial counterpoise or ground system, not a "Tee" antenna. There are no horizontal wires connected and radiating from the top of the tower as would be the case with the "Tee" antenna. Return RF currents are induced in phase and equally in the radial counterpoise which is excited by RF from the monopole antenna.

 

[rfry]

here are no horizontal wires connected and radiating from the top of the tower as would be the case with the "Tee" antenna. Return RF currents are induced in phase and equally in the radial counterpoise which is excited by RF from the monopole antenna.

Yet the tee antenna accurately illustrates the point. That same pattern envelope applies to a monopole over a symmetrical set of buried radials, as is shown in standard antenna engineering textbooks (Kraus, etc).

It doesn't matter to the physics of radiation if r-f current is injected at the center of a linear conductor, or collected from the currents induced in the earth by a radiating monopole at the connecting point of a linear pair of buried radials.

The far-field radiation in both cases is zero, because the radiation from each side of such conductors always travels in opposite physical directions, which causes a phase reversal in their respective radiated fields -- which results in zero net radiation.

//

 

[rfry]

The far-field radiation in both cases is zero, because the radiation from each side of such conductors always travels in opposite physical directions, which causes a phase reversal in their respective radiated fields -- which results in zero net radiation.

Correcting my statement above, for better comprehension:

The far-field radiation in both cases is zero, because the current in each side of such conductors always travels in opposite physical directions, which causes a phase reversal in their respective radiated fields -- which results in zero net radiation.

//

 

[Neil E.]

When I wrote:

The field radiated from the north antenna by current going south produces an equal and opposite field to cancel that produced in the south antenna with the current going north. Since the currents are equal and opposite in direction in the radials the fields are also equal and opposite and cancel.

I should have use the term radial or conductor rather than antenna to avoid confusiion with the vertical monopole element. Sorry about this.

Supercaster, in response to your comments:

No.
The observer receives only the wave front headed toward him and not the radial wave front headed in other directions.

The observer can move around the system and the wave fronts produced by the two short radials in the system we are discussing will still always be 180 degrees out of phase upon reaching the observer and will cancel.


The lobes I mentioned were for two radials not 180 degrees opposed, and that is not what is being discussed.

Remember:
The observer receives only the wave front headed toward him and not the radial wave front headed in other directions. They are headed elsewhere.
Waves headed in other directions never reach the observer's radio, unless they bounce off something and return (multipath) or travel around the world.

Isn't this similar to "if a tree falls in a woods and no one is there does it make a noise"? Position the observer anywhere you want and the wavefronts reaching him from the radials will cancel.

You have probably seen the link Mr. Fry posted here illustrating the filed produced by the "tee" antenna. Note that in the horizontal plane there are no lobes and no radiation produced by the "tee" element on top of the antenna. This is the same result as will be seen by studying the net field produced by 180 degree opposed radials, namely no net radiation.

Neil

 

[SUPERCASTER]

R. Fry said:

Yet the tee antenna accurately illustrates the point. That same pattern envelope applies to a monopole over a symmetrical set of buried radials, as is shown in standard antenna engineering textbooks (Kraus, etc).

No, it does not illustrate anything of the sort. The "Tee" antenna has 2 driven elements, the driven vertical, and the driven horizontal top conductor. It does not model, equal, or replace a vertical monopole with ground radials, which has one vertical driven element, and a ground system. Clearly the horizontal top of the Tee does not model or replace a radial ground system. The two are not even similar, in performance or engineering. The idea that a Tee antenna and a vertical monopole with ground radials are equivalent antenna systems is ridiculous.
Tee antennas used by early broadcasters have all been replaced by much better (but more expensive) vertical monopole's with radial ground systems, proving no equivalence.

 

[SUPERCASTER]

The currents of 2 or more in phase conductors are additive and do not cancel.
RF driven "top hats" added to vertical monopoles do radiate a far field signal. That is why they are used, and not as a replacement for ground radials. The two are not equivalent.

 

[SUPERCASTER]

With a verticle monopole antenna system centrally mounted over ground radials:
The omnidirectional RF field from a vertical monopole travels out from the monopole in a phase coherent circular pattern. Think of a round rock dropped vertically into a pond and the round concentric phase coherent waves that result. The part of the wave heading in one direction does not interfere or null the wave traveling in the opposite. The direction of the wave is omnidirectional and has have no cancellation effects on the part of the wave traveling in the opposite direction. They do not cancel at all!
The radial ground system responds to the doughnut shaped circular radiation pattern, closes the circuit to the transmitter ground allowing current to flow and far field radiation to occur. No cancellation occurs.
All currents remain in phase/additive to far field radiation and none of the RF cancellation effects you claim occur from either the circular radiation pattern form the monopole tower or the coherent circular current return through the ground system.

The efficiency of this widely used antenna system is excellent because no power wasting cancellations occur.

 

[rfry]

The omnidirectional RF field from a vertical monopole travels out from the monopole in a phase coherent circular pattern. ...The direction of the wave is omnidirectional and has have no cancellation effects on the part of the wave traveling in the opposite direction. They do not cancel at all!

The radial ground system responds to the doughnut shaped circular radiation pattern, closes the circuit to the transmitter ground allowing current to flow and far field radiation to occur. No cancellation occurs.

No one has written here that such cancellations occur for the radiation from a vertical monopole with buried radials.

What has been written here is that the far-field radiation from the r-f current flowing in two radials running in opposite directions from the base of the monopole will cancel each other. The reason for this is, that even though currents in the two radial wires are of equal amplitude and phase-coherent, they are always traveling in opposite physical directions in those wires. This produces a relative phase reversal between the fields generated by the two radials, which results in zero far-field radiation from that pair of radials.

If this was not true, then the total radiation envelope from a vertical monopole with buried radials would not have a null toward the zenith (directly above the monopole). Since you posted knowledge that the radiation pattern of a vertical monopole has a "doughut" shape,* then you should recognize that this would not be possible unless the radials were behaving as I have stated with respect to their net radiation. For verification of this you may want to review the appropriate chapters of a good textbook on antenna theory. Also all of these statements can be confirmed rather easily using Numerical Electromagnetics Code (NEC).

As you have correctly noted, the function of the radials is to collect the r-f currents induced into the earth by radiation from the monopole, and to return them to the transmitter system with minimum losses. Such losses are in series with the antenna current, and they need to be minimized in order to maximize the radiation efficiency of the antenna system.

* really, a doughnut sliced in half across its greatest width

//

 

[rfry]

RF driven "top hats" added to vertical monopoles do radiate a far field signal. That is why they are used, and not as a replacement for ground radials. The two are not equivalent.

The horizontal wire of a tee antenna radiates no field by itself, because the currents in the two sides of it always are flowing in opposite physical directions -- which means that the fields each side produces are out of phase with each other, and cancel. Engineering textbooks and NEC will verify this.

The horizontal part of a tee antenna raises the radiation resistance of the vertical wire, and changes the current distribution along it. Both of those improve the field radiated by the vertical wire, other things equal.

Tee antennas need as good an r-f ground (or better) as a vertical monopole. The horizontal part of the tee does not replace a good r-f ground, and no one here has stated that it did. It just improves the radiation efficiency of an electrically short vertical antenna system.

//

 

[rfry]

The idea that a Tee antenna and a vertical monopole with ground radials are equivalent antenna systems is ridiculous. Tee antennas used by early broadcasters have all been replaced by much better (but more expensive) vertical monopole's with radial ground systems, proving no equivalence.

Tee antennas need a good r-f ground for the same reason that monopoles need one.

If you look at the radiation envelope of the tee antenna at this link I posted earlier http://i62.photobucket.com/albums/h85/rfry-100/TeeAntenna.gif, you will see that it has the same shape as that of a monopole.

Tee antennas were used in broadcasting when good performance was required from electrically short antennas. When tall steel towers that approached or exceeded 1/4-wavelength began to be used, then "top loading" no longer was required to achieve high radiation efficiency from the antenna system, and tee antennas generally were no longer needed/used for MW broadcasting.

For a detailed treatment of tee and monopole antennas you might read Performance of Short Antennas by Carl E. Smith, published in the October 1946 issue of The Proceedings of the Institute of Radio Engineers.

//

 

[Timewarp]

OK. You guys have been so technical that you have surely confused 99 percent of the
part 15ers. I know what you are saying, I'm an engineer with plenty of experience.
What's the point. As engineers, we all know that real world is not the same as paper.

Next point. The FCC is going to accept applications for FM NCE licenses in October. The
Commission would like guys such as you to get a license. Frequencies are open all
over the USA. You can use http://recnet.com/ to find a channel for free. You can
start a not for profit corpoation yourself. You can apply with the FCC free of charge.

If your smart enough to talk this stuff, then you are bright enough to get an FCC
license and they are free.

 

[SUPERCASTER]

A counterpoise radiates and may change the true antenna's radiation pattern.

http://www.smeter.net/grounds/c_poise.php

Here are more tips for community broadcasters, where regulations permit:

http://groups.msn.com/GospelRadio/foldedunipolespagetwo.msnw

 

[rfry]

A counterpoise radiates and may change the true antenna's radiation pattern.

However the discussions in this thread have concerned either the horizontal part of a tee antenna, or buried ground radials -- not a counterpoise.

But regardless, a properly-designed counterpoise used with a monopole will produce a radiation pattern and peak gain that is very close to that of a monopole used with a 120 buried radials, each 1/4-wave long, as experience and NEC will illustrate.

This configuration sometimes is used for AM broadcast stations installed at sites where the earth is mostly rock.
//

 

[Neil E.]

The currents of 2 or more in phase conductors are additive and do not cancel.
RF driven "top hats" added to vertical monopoles do radiate a far field signal. That is why they are used, and not as a replacement for ground radials. The two are not equivalent.

The equivalence between the top hat wires and the radial wires was only to illustrate that the fields from each cancel by the same mechanism, not to imply that the two systems serve the same purpose.

Repeating, in new words, what I have already said, you are entirely correct that the currents in the radials or a center driven top hat are in temporal phase with 0.0 degree phase shift and they add, but because of the 180 degree angle between the radials the radiated fields produced by these two conductors are 180 degrees out of phase and they cancel. Add two equal amplitude and frequency 180 degree out of phase signals and you get 0.0, whether they be volts, amps. or RF fields. It should help if you keep in mind the distinction between the currents and the fields.

The summation of currents where the radials connect together does not depend on the physical direction from which the currents enter this node because the current phase is not a function of the direction, but the phase of a radiated field produced does depend on the conductor direction. The key here is that though the currents are adding at the node , the currents are travelling in opposite physical directions in the opposed radials and this is what makes the fields 180 degrees out of phase and the fields add to zero.

There may be a better way to explain this but this is the best I can do, and I am getting repetitous. Perhaps, as Mr. Fry suggested, you could consult an antenna engineering text on this and report back when you find this is incorrect.

Neil