Part 15.219(b) rule

[radiopilot]

Again, the rule just simply says nothing about radiation.

No, but it does say that the transmission line, antenna and ground lead (if used) cannot exceed 3 meters.

Some have decided that only a fraction of the length of the conductor(s) connecting the Part 15 AM transmitter to a functional r-f ground needs to be included in that 3 meters.

Physics shows otherwise. That entire conducting path is the "ground lead," and if excessive, can be cause for an FCC citation -- as per some recent examples.
//

It's funny that most of the FCC citations for 'excessive' ground leads have happened since you've been on these and other boards and perhaps the FCC is monitoring these boards for FCC rule interpretation.

Now most of the citations are for 'excessive' ground leads and are in the manner of 90 feet, as the case for the 'Iglesia de Dios' citation of which I believe this was the third citation for this church, so I think the FCC was hounding this church group for more than the 'ground lead' and more for the complaints to it by the community or overly jealous competitors.

But most of the part15 broadcasters are using reasonable ground leads as I have (30 feet) and the FCC agent out of Atlanta came twice to see my setup and had no problem, in fact he offer to help my station further, and just as many of Hamilton’s customers have provide proof that their stations are FCC inspected and passed, so by you offering this so called 'physics' knowledge onto the already informed community you may wind up hindering that offer of help.

No one can actually believe that the 'transmission, ground lead, and antenna' can be 3 meters exactly to the millimeter, as there is the power cord which is grounded, the leads from the sound source to the transmitter and any length of ground lead to the rf ground is going to be greater than the 3 meter length no matter how you devise the system and the FCC is aware of this, that is WHY they give some latitude and people like you that take literally words written to be gospel.

I think you are knowledgeable and worthy of respect, but I must say you make poor judgments on how other might view their interpretations even if it's contrary to what you might read into it.

Allot of competent and certified engineers do not take your views and why should the FCC if they are reading these boards only accept your views?


Radiopilot

 

[Hamilton]

Thank You Radio Pilot,
I actually talked to the guy who sold the transmitter to the 'Iglesia de Dios' and apparently the FCC was denied access and ignored. Often the "Ground lead violation" is the only weapon they have against the bad guys.
And yes, Fry you are using bad judgment here, you are hurting a lot of good people by extrapolating to the worse possible degree possible what should be a simple situation.
People have to live in the real world and this Part 15.219 rule is a great rule designed to regulate in the real world. Can you not admit that maybe the FCC knew what they were doing when they wrote the rule and just leave the individual interpretation up to the FCC? A “lead” is a wire! A “lead” cannot be some insane conducting path all over the Lord knows where!

 

[rfry]

William Walker, Radiopilot, Keith Hamilton and I all have presented our cases on this subject matter. There's nothing new to add.

Hopefully other readers will process and research this information, and make an educated decision about which course they want to follow, and what risk level that entails.

//

 

[radiopilot]

William Walker, Radiopilot, Keith Hamilton and I all have presented our cases on this subject matter.  There's nothing new to add.

Hopefully other readers will process and research this information, and make an educated decision about which course they want to follow, and what risk level that entails.

//

What the user will get from reading these posts is still more confusion as the FCC can and WILL shut you down even if the transmitter is mounted to the ground (soil) with only a true 3 meter length from antenna to ground if they want to based on complaints from others such as licensed stations even though you are part15 complaint.

So no matter which route you take there is always interpretation by the FCC agent at hand and no amount of our squabbling here is going to change that. There is no magic bullet, but rationalizing it here on this board doesn't help the part15 community any, set up your transmitter, ground, etc. broadcast and see where the chips fall.

The FCC agents are not tyrants out there in mass droves seeking violators, they have to get a compliant first before they come out for an NOUO, so make the first contact with the FCC and inform them of your intentions, surely they WILL overlook a ten to twenty foot ground lead, even if as RFry says they are not 'physics' informed, who knows maybe science was not their strongpoint, BUT they are the last word on the matter and not RFry.

Yes we all presented our cases and when other informed users get that same results from the FCC agents he too will be able to post his/her knowledge and observations whether they are for or against the part15.219 rule.

Radiopilot

 

[Neil E.]

I have a question. If I set up my AM part 15 transmitter with a 3 meter long wire antenna and I "tie off" the end of this wire to another conductor, is my antenna still legal? Does the wire nut demark the length of the antenna?

Neil

 

[Black_Shire]

I have a question. If I set up my AM part 15 transmitter with a 3 meter long wire antenna and I "tie off" the end of this wire to another conductor, is my antenna still legal? Does the wire nut demark the length of the antenna?

Neil

That's a good question. All of the FCC Certified Part 15 AM transmitters (the Rangemaster, LPB AM2000, TalkingSign, and Talking House, as well as all of the kit Part 15 AM transmitters) have unbalanced outputs--that is, in each of them the antenna is a monopole over an RF ground of some sort, which varies depending on the transmitter model. That is why the antenna length is of greater interest to FCC Field Agents.

If there is DC continuity across the "tie-off" point you described, it isn't legal because the antenna is then a (3 + X) meter long wire.

If the 3 meter wire antenna and the other piece of wire are connected via an insulator (a glass strain insulator, a plastic button, etc.) and have no DC continuity between them, it might or might not pass an FCC inspection depending on the specifics of the installation.

If the other wire is just a support wire coming down from a higher object such as a tree or a telephone pole and is holding the 3 meter wire antenna up, it would probably pass in many if not most cases. However, if this antenna support wire "just happens" to be 1/4 wavelength long and its far end is held up by a balloon or a tall tower, well...let's just say I wouldn't try it myself.


-- Black Shire

 

[WCWalker]

Blackshire, technically this is not true. Therein lies the problem with R. Fry's comments. He claims everything in the chain that radiates is considered to be the antenna. That simpy is not true. Hence my references to differing bodies of water as an analogy to show he's wrong. Just because you have water/energy running through a different component does not define it as a antenna. People also seem to forget the transmitter itself (Rangemaster or USI Trans AM 100) radiates signal yet the FCC does not consider that to be part of the transmitter. If they did then virtually EVERY installation out there would not meet Part 15 requirements.

By definition the transmitter is not an antenna or ground lead. Neither is the mast or the surge arrestor. They ARE prcecisely what they are. If they are not then the must be redefined as either a ground or antenna and should never be called a mast or surge arrestor. Just because current radiates through these parts of the chain does not redefine their given names. The FCC may or may not cite an operator for running a continuous length of copper wire from the transmitter to the ground but that seems to depend on the mood of the field agent. I have never seen or heard of an FCC agent citing an operator that has tied off the foot and a half wire to another object.

It's so simple that people are overlooking the obvious. Unless Webster's Dictionary and the FCC decides to change the name of definition of the Surge Arrestor, or tie off point, the mast and transmitter they must be considered what they are regardless of whether or not they radiate. Nothing in the FCC rules states these objects are part of the antenna or ground simply because they may radiate some rf.

 

[phatdaddy]

I would like to add my thoughts to this very interesting discussion. For illustration, lets assume we have a ground-mounted Part-15 transmitter with a 10 foot radiator and a number of evenly spaced ground radials either laying on the ground surface or perhaps buried a few inches below ground. As the signal is radiated from the 10 foot antenna there are "return currents" being collected by and flowing through the radial system back to the transmitter. As there is RF current flowing through these conductors, in theory they would radiate however any radiated signal is absorbed by the ground surrounding the conductor. In effect, the radial system is creating a virtual mirror image of the antenna below the ground and the antenna functions basically as a vertical dipole.

Now if we were to elevate the transmitter and it's antenna by several feet and connect it to the radial system with a piece of wire, the RF currents flowing from the radials through the interconnecting wire to the transmitter would create a certain amount of radiation in addition to that created by the antenna. In this case it seems logical that an FCC inspector would consider the short vertical wire to be a portion of the antenna system as spelled out in 15.219.

If we were to then move the transmitter and install it in the center of a large metal-roofed building with only a short jumper between the transmitter chassis and the metal roof, this roof would function as the radial system for the transmitter and collect the RF currents returning to the transmitter. I feel that although there are RF currents flowing through the roof structure, any radiation would be minimal due to the relatively large capacitance between the roof and the soil below. In this case the roof could be considered to be the "ground reference" for the transmitter and it's antenna. If an inspector were to inspect such an installation, it is most likely that he would only consider the length of the whip antenna and the length of the jumper between the transmitter and the metal roof.

 

[Black_Shire]

Blackshire, technically this is not true. Therein lies the problem with R. Fry's comments. He claims everything in the chain that radiates is considered to be the antenna. That simpy is not true. Hence my references to differing bodies of water as an analogy to show he's wrong. Just because you have water/energy running through a different component does not define it as a antenna. People also seem to forget the transmitter itself (Rangemaster or USI Trans AM 100) radiates signal yet the FCC does not consider that to be part of the transmitter. If they did then virtually EVERY installation out there would not meet Part 15 requirements.

By definition the transmitter is not an antenna or ground lead. Neither is the mast or the surge arrestor. They ARE prcecisely what they are. If they are not then the must be redefined as either a ground or antenna and should never be called a mast or surge arrestor. Just because current radiates through these parts of the chain does not redefine their given names. The FCC may or may not cite an operator for running a continuous length of copper wire from the transmitter to the ground but that seems to depend on the mood of the field agent. I have never seen or heard of an FCC agent citing an operator that has tied off the foot and a half wire to another object.

It's so simple that people are overlooking the obvious. Unless Webster's Dictionary and the FCC decides to change the name of definition of the Surge Arrestor, or tie off point, the mast and transmitter they must be considered what they are regardless of whether or not they radiate. Nothing in the FCC rules states these objects are part of the antenna or ground simply because they may radiate some rf.

Neil was asking about the legality of connecting (with a wire nut, in his example) the far end of the 3 meter wire antenna to another length of wire. If there is DC continuity between the two pieces of wire, then they form a larger antenna that is greater than 3 meters in length, which is clearly illegal.

If the 3 meter wire antenna is connected to the other length of wire in such a way that there is no DC continuity (using an insulator of some kind) at the point of connection, then it might or might not pass an FCC inspection depending on the specifics of the installation.

If the other wire is obviously intended to be parasitically excited by the 3 meter antenna to re-radiate (the other wire being a resonant length or having a loading coil to be resonant), it might very well get a "thumbs-down" from an FCC inspector. If the other wire is some non-resonant length and is just being used to hold up the 3 meter wire antenna (the other wire being suspended from a tree or a pole), it would be more likely to pass an FCC inspection.


-- Black Shire

 

[Neil E.]

The intent of my question regarding extending an antenna with a "tie on" wire was leading to the point that doing the same to the ground wire might be interpreted as an extension of the ground which results in exceeding the total length rule.

There appears to be two interpretations in this thread which have resulted in some unkind comments and accusations. Let's put personal issues aside for a moment.

One interpretation, which I agree with, is that the ground lead length is the measure of all conductors leading into the dirt. This is based on my understanding of the intent of 15.219 b to limit the field strength and takes into account that above ground conductors of RF will radiate and enhance field strengh.

The second interpretation is that the FCC inspectors have passed systems with long ground leads, such as is found with "elevated" AM transmitters. I have no reason to doubt the information posted by those who say this is true.

Though the FCC inspectors may give a pass to these elevated systems it does not redefine what is stated in the rules, nor does it define a ground lead. A police officer who allows leeway on the posted speed limit does not redefine the actual speed limit.

If an operator is comfortable with the assurance that few AM operators get into trouble with extended grounds and chooses to operate this way, that is fine with me. I believe what Mr. Fry and myself are presenting is an interpretation of the 15.219 b rules which is based on physics and engineering principles. I am a degreed, practiced, and licensed engineer (not in title only as is very common), and unlike those who were referenced in an earlier post who were paraphrase quoted as:

If you approach an engineer that knows nothing about part 15 and show them the rule I have found that 100% of the time the term “Ground lead” is clear, the wire from the transmitter to the tower, mast or other local ground. When I mention that some people are trying to interpret “Ground lead” as “the entire conductivity between the ground terminal of the transmitter circuit board and the dirt” some of these engineers have gone ballistic on me trying to explain to me how ridiculous that is.

I do not accept as ridiculous the claim that “the entire conductivity between the ground terminal of the transmitter circuit board and the dirt” is the RF ground, and doubt that a professional engineer, familiar with part 15 or not, would compromise professional demeanor by "going ballistic".

The attempts to redefine what is meant by grounds and ground leads are interesting but futile as viewed by me. Using anecdotal stories about the descretion of inspectors to design your station is rolling the dice. Go for it if that is what you want to do.

So, with this as background, you have read both views of the topic. You can choose to observe the part 15.219 rules as written as I interpret them or you can base your decisions on reports of what the FCC inspectors have done and might do. Just keep in mind that enforcement descretion does not redefine the law.

Neil

 

[Flying-Dutchman]

Once upon a time, I had a conversation with a friend about part 15 AM. A good man and the Engineer
in Charge of a midwest FCC field office. He told me about a low power AM that had strapped on to a
tower. The ground strap went through the tower.

He told me that because the tower was pre-existing it was fine. The key was pre-existing.

You are limited to 100 mw input unless you are a school in which case you can have more power.

No more than 10 foot of antenna. It must be called a kit. Always cooperate with the FCC.
Failure to allow an inspection is a $17,000 fine. Have Fun!

 

[Neil E.]

Once upon a time, I had a conversation with a friend about part 15 AM. A good man and the Engineer
in Charge of a midwest FCC field office. He told me about a low power AM that had strapped on to a
tower. The ground strap went through the tower.

He told me that because the tower was pre-existing it was fine. The key was pre-existing.

Thanks for the anecdote. Once again it appears this was a matter of discretion. In the rules there is no mention of "pre-existing".

Neil

 

[Hamilton]

I think “practical” is a key word here. The definition of “the entire conductivity between the ground terminal of the transmitter circuit board and the dirt” for ground lead seems ridiculous to me because, first of all that isn’t a “lead” or “wire” and requiring all Part 15 devices, indoor and outdoor models to be mounted at the dirt is simply impractical. The basic 15.219(b) rule is a great simple and practical rule.
I think even though 15.219 say nothing directly about limiting radiation in the ground the ground lead is attached to, some agents believe the ground should not radiate because of the spirit of the law.

“One interpretation, which I agree with, is that the ground lead length is the measure of all conductors leading into the dirt. This is based on my understanding of the intent of 15.219 b to limit the field strength and takes into account that above ground conductors of RF will radiate and enhance field strengh.

The second interpretation is that the FCC inspectors have passed systems with long ground leads, such as is found with "elevated" AM transmitters. I have no reason to doubt the information posted by those who say this is true.”

A more accurate stating of the other side I think is that some agents take 15.219 (b) “literally” or “at face value” without adding anything of their own.

 

[Neil E.]

A more accurate stating of the other side I think is that some agents take 15.219 (b) “literally” or “at face value” without adding anything of their own.

It is not clear to me which view you reference as the "other side" but if I assume that this is the one where the ground lead ends at the connection to a conductive structure then this contradicts what I thought was a "literal" interpretation. But, we argue semantics here don't we?

There are examples related where "elevated" installations pass inspection and there are examples where they fail inspection. You are correct that a key word is "practical", especially if a particular station is inspected and not cited. But it seems that if another station is inspected and cited practical turns into impractical, at least for that operator.

It is good to discuss this since it provides information which can be used by part 15 AM operators as they plan their installations since they can study alternative views of this issue. Thanks for your contributions.

Neil

 

[RadioMan203]

Once upon a time, I had a conversation with a friend about part 15 AM. A good man and the Engineer
in Charge of a midwest FCC field office. He told me about a low power AM that had strapped on to a
tower. The ground strap went through the tower.

He told me that because the tower was pre-existing it was fine. The key was pre-existing.

You are limited to 100 mw input unless you are a school in which case you can have more power.

No more than 10 foot of antenna. It must be called a kit. Always cooperate with the FCC.
Failure to allow an inspection is a $17,000 fine. Have Fun!

Can you cite me the particular section of Part 15 that allows schools to have more power? I'm working with a high school that would love to have a radio presence, but I honestly don't believe there is any instance where Part 15 allows any operation past 100mW

 

[Neil E.]

Bill,

It is in part 15.221 which is quoted in part here. You need to read the whole thing.

b) ...operation of an AM broadcast station on a college or university campus or on the campus of any other
education institution may comply with the following:
(1) On the campus, the field strength of emissions appearing outside of this frequency
band shall not exceed the general radiated emission limits shown in Section 15.209 as measured from the
radiating source. There is no limit on the field strength of emissions appearing within this frequency
band, except that the provisions of Section 15.5 continue to comply.
(2) At the perimeter of the campus, the field strength of any emissions, including those
within the frequency band 525 - 1705 kHz, shall not exceed the general radiated emissions in Section
15.209.
(3) The conducted limits specified in Section 15.207 apply to the radio frequency voltage
on the public utility power lines outside of the campus. Due to the large number of radio frequency
devices which may be used on the campus, contributing to the conducted emissions, as an alternative to
measuring conducted emissions outside of the campus, it is acceptable to demonstrate compliance with
this provision by measuring each individual intentional radiator employed in the system at the point
where it connects to the AC power lines.

The key is in section (2) where the field strength is specified at the perimeter of the campus which would allow any power needed to produce this result. The down side is testing to ensure compliance with this requirement.

Hope this helps.

Neil

 

[carlvenorden]

I am in agreement with Mr. Walker and for the most part Mr. Hamilton, as the "builder" of the sstran antenna.

We did a couple of things with our antenna, which differs quite a bit from the Radio Shack 108 whip/12" ground lead the Rangemaster uses.

But there are similarities as well.

We too felt that the ground lead ought to be as short as could be so that it would be legal, and basically, unquestionable as to it's legality. But to do that, and insure a tx wouldn't be fried by lightning, the ground wire is attached to a short (or long) iron mast pipe just inches from the transmitter by a simple screw. The mast pipe may or may not have radials attached to it underground, but those radials are meant to catch antenna signal like the big boys, not to elongate the antenna length.

Our ground lead may never approach the 108 inch limit including the length of the antenna because our antenna needs to be tuned in order to radiate correctly. Therefore, none of our antennas are ever fully 108" long........they are always shorter, and in some cases depending on the tap of the coil, could be a foot or more shorter.

We felt that the iron mast pipe was not part of the ground, but an end to it as it is not a continuous wire INTO the ground.

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.

If a customer hooks the antenna up in another manner, well, that could change, but the specs on our antenna show that below the insulator, there is little to no radiation (at least nothing that would contribute to the actual signal strength).

So, I do wonder why the Rangemaster "needs" (if it does need) an 18" ground wire, and it certainly could be shorter if attached in the same manner we attach ours. And I believe it basically ties off the same way. If so, I don't see any infraction in the rules either for the Rangemaster or for the sstran.

And certainly, anyone involved in building these units/antennas does not need or want FCC involvement, so we tend to stick by the rules to avoid those issues.

Ground systems don't generally radiate, and at 100mW, they certainly don't. They do provide lighting protection and force signal out onto the ground the way a conventional AM station does. ...thus improving the signal. It is not an extension of an antenna anymore than a ground rod is...because if a ground rod is, and that ground rod could be 5-10 feet long for lightning protection, we are ALL operating against the rules in one way or the other.

The long and short of it is: regardless of the reason for a ground, these units MUST be grounded as legally as they can be, otherwise we would all loose our investments to lightning. Pure and simple.

 

[rfry]

But to do that, and insure a tx wouldn't be fried by lightning, the ground wire is attached to a short (or long) iron mast pipe just inches from the transmitter by a simple screw. The mast pipe may or may not have radials attached to it underground, but those radials are meant to catch antenna signal like the big boys, not to elongate the antenna length.

Regardless of what they are "meant" to do, buried radials will increase the radiation both from the conductors leading up from them to the transmitter via the mast and and "ground lead", and from the 3-m whip, itself. They do this by reducing the series r-f resistance for the currents induced in the earth via radiation from the antenna system -- which need to be returned to the tx chassis.

We felt that the iron mast pipe was not part of the ground, but an end to it as it is not a continuous wire INTO the ground.

Electrically connecting two or more conductors in series provides a continuous path for current flow, the same as if a single conductor was used.

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.

NEC analysis of elevated Part 15 AM systems with a long, conducting path to a buried r-f ground show otherwise. So do the results of users of these installations, which probably is the real reason for installing them this way. If your measurements aren't showing this then the instrumentation and/or methodology probably need to be changed.

Ground systems don't generally radiate, and at 100mW, they certainly don't.

A functional r-f ground will not radiate. That's the definition of an r-f ground.

But an r-f ground does not exist at the top of a conducting path leading from its connection to buried radials or ground rods up to a Part 15 AM tx mounted on a flagpole, mast or billboard.

That conducting path may have only a few milliohms of DC resistance when measured end to end, but it will have considerable resistance (impedance) to the flow of r-f energy. That condition adds to the radiation resistance of the antenna system, which will increase the field strength it will produce, other things equal. And that will be true for transmitters of 1 kW, 100 mW, 1 pW, and every other power level.

So the only functioning r-f ground in such systems is what is buried in the earth. The total length above the surface of the earth of all conductors leading up from it to the elevated tx/antenna comprise the true "ground lead" for these systems.

//

 

[Hamilton]

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.
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?

 

[rfry]

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.

Experimental data showed back in 1937 that given a sufficient number and length, a set of radials produced an r-f ground of less than two ohms. This was done in the sandy soil of New Jersey (conductivity about 4 mS/m -- very poor). But even if buried radials did radiate, any such far-field radiation would be horizontally polarized, and add nothing to the field radiated by the vertical radiator in the horizontal plane (the ground wave).

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?

NEC shows an impedance of 0.137 -j 3145 ohms at/near the base of a 3-m, vertical, 1/2" OD copper pipe on 1700 kHz, mounted with its base at the surface of a perfect earth. I used 1700 kHz because I already had some NEC models set up for that frequency.

When that same system is elevated 7 meters above the earth, and a 7-meter ground wire connects it to a perfect earth, its base impedance changes to 3.2 -j 3100 ohms.

Note that on 1700 kHz, the R term of even the earth-mounted vertical is almost 22 times greater than its DC resistance.

Only the radiation resistance is capable of usefully dissipating r-f power (by radiation). So it is clear that the elevated system will be the better performer of the two, and by a considerable amount.
//