Part 15.219(b) rule

[Timewarp]

I am just amazed at the passion displayed over one tenth watt and ten feet of antenna on AM.

 

[dbdigital]

I am just amazed at the passion displayed over one tenth watt and ten feet of antenna on AM.

Part of this is the joy of simply discussing the technical aspects of radio and electromagnetic propagation among guys who have an understanding and passion for it. The other part is sifting through vague FCC rules governing Part 15 and coming up with a definitive standard. The later is where some have suggested we could get into trouble.

Apparently it has been proven that employees within the FCC do read these sites and if an intense debate is raging over an FCC regulation, especially one regarding unlicensed operation, it could very well come up on the agency's radar. This might, in turn, result in, at the very least, an internal memo to FCC agents as to what constitutes a proper Part 15 AM set up. As it is, there is some interpretation and leeway involved on the part of agents who inspect such sites as to what is and what is not legal.

100 mW may not sound like much but imagine if a dozen type-accepted TXs were set up around a town and pumping out the same programming. You could do some serious community broadcasting with that. For many of us that is an exciting prospect.

db

 

[Timewarp]

I am not against part 15. I am for it. But you guys need to take your arguments before the
FCC. It is no more trouble than debating here.
You should try to get more power and more antenna. What could it hurt. AM has very few listeners
left.

A watt into a long wire is barely worth doing. But it is better.

 

[Hamilton]

Part 15 I think is important; it is a big world out there. There are many services beyond the hobby world that use the service, Schools, Parks, Churches, government entities and businesses use it for parking information all over the country. Lately it is being used for homeland security in some areas. I got into it as a boy when I built a 50C5 tube Part 15 AM transmitter and broadcast to my neighborhood. So hashing out and defining these rules is important to and affects a lot of folks. I agree though it is the FCC that will define and/or make the rules.
Talking about wave physics and their characteristics is very useful. It is the folks that understand wave and antenna theory that get the great range with Part 15.

 

[dbdigital]

I am not against part 15. I am for it. But you guys need to take your arguments before the
FCC. It is no more trouble than debating here.
You should try to get more power and more antenna. What could it hurt. AM has very few listeners
left.

A watt into a long wire is barely worth doing. But it is better.

In a way, these arguments were taken before the FCC in the form of the Baumgartner Petition of June 2003 and the Don Schellhardt Petition of August 2005 for an LPAM service. As we well know, nothing has come of them so far. In contrast, when the satcasters announced a desire to merge last year the FCC, the FTC, Congress and whole cast of shady characters (ex-congressmen, NAB lobbyists and the like) jumped on it like flies to decaying meat.

By the time the FCC gets around to ruling on LPAM, the AM band will be long dead instead of just gasping for breath as its doing now.

But on a different note, I was cheered to read in the Orange County Register about the Saddleback College Summer School program for kids ages 8-11. One of the classes is on building an AM radio using transistors. At the end of the class the kids will learn basic electronics and get an AM radio in the process. It would be great to see a program like that implemented throughout the country.

Maybe the kids will discover AM radio on the little receivers they built with their own hands.

db

 

[Flying-Dutchman]

I remember when AM was KING. That was 30 years ago. If AM is to be revived or saved,
local programming, unique programming, and community radio are it's only hope.
If this is not done soon it will be too late to save AM. It will go bye bye just like the
reel to reel tape recorder.

 

[Tom Wells]

Returning to the topic of vertical monopole/radial radiation and cancellation, I have reviewed my notes from Valpo Tech.
This same argument regarding groundwave radiation came up in class.
The consensus was that if you take a vertical antenna, and add 2 radials, they "cancel", but squeeze radiation into two lobes.
Four radials, four lobes, and so forth. By the time we get to 80 or 120 radials, we have created a pattern like a flower with many radial spokes, the general effect of which is combinant, and the result is 360 degree coverage.
This also presumes our radiator has inherent L and C, regardless of loading coils or capacity hats, which assist current in the radiator.

I was truly enjoying the debate over this. It's too bad we came to an impasse.
Can anyone else support this position or offer another explanation for the seeming disagreement between radiation/cancellation?

 

[Black_Shire]

The presence of the soil may make a difference in whether or not there are lobes off the ground radials. If you lay a dipole antenna on the ground, the horizontally-polarized radiation broadside to the antenna is absorbed by the soil and it has two lobes of vertically-polarized radiation, one off each end. (It has a vertical lobe too, which makes Near-Vertical Incidence Skywave [NVIS] propagation possible.)

The CIA and the Soviets both used (and may still use) shallow-buried clandestine "wagon wheel" antenna facilities of various sizes for Long Wave through Short Wave operation. They were multiple crossed dipoles that looked like an AM radio station's buried radial system (but with fewer "radials," in this case). Their operators took advantage of the "end-fire" lobes of the buried dipoles to achieve directional patterns by feeding differing amounts of power to the various dipole elements.

A few months ago I was reading an account of the adoption of VHF radio by police departments. (The old police radio band was roughly where the AM expanded band is today, and police cars of that era often used helical wire antennas wrapped around 10 foot tall bamboo poles that were mounted on their rear bumpers.)

The engineer/entrepreneur who was promoting VHF radios to police departments used a ground plane antenna that had only two radials (a 1/4 wavelength vertical radiator over the center of a horizontal 1/2 wavelength conductor). When potential customers voiced concern that the two radials might "pull most of the signal in those two directions," he added two more radials at right angles to the first two.

According to the article, both antennas were omni-directional in azimuth and had nearly identical efficiency, the four-radial version having a slightly lower feed point impedance than the two-radial version.


-- Black Shire

 

[rfry]

Returning to the topic of vertical monopole/radial radiation and cancellation, ... I was truly enjoying the debate over this. It's too bad we came to an impasse. Can anyone else support this position or offer another explanation for the seeming disagreement between radiation/cancellation?

___________

Hi Tom,

Buried radials reduce I^2R losses for the r-f currents induced in the earth via radiation from a nearby vertical monopole antenna system. For best radiation efficiency these r-f currents need to be returned to the transmission system.

Other things equal, more and longer buried radials will increase the tx power available for radiation by a monopole antenna system. This is the conclusion based on calculated and measured data by RCA broadcast engineers (George Brown, et al) going back to 1937, and proven by many 1000s of accurate, real-world field strength measurements with calibrated field strength meters ever since. Of course, all antenna engineering textbook and accurate NEC analyses also support this.

A vertical monopole and its complete conducting path to a true r-f ground reference (not just the short wire defined by some as the Part 15 AM "ground lead") are the only source of useful radiation from such a system. They radiate a uniform field strength in all horizontal directions, whether using 1 or 120 buried radials, or just a ground rod or two. The only difference is that a monopole system with more/longer radials will generate a greater absolute groundwave field strength at a given distance, and will do so in all compass directions (again, other things equal).

Elevated radials behave differently. Any symmetric set of 2 or more radials about 1/4-wave long each, when used at the base of a vertical MW monopole, and elevated 15 feet or so above the earth will produce about the same result as that same vertical monopole used with 120 buried radials, each about 1/4-wave long. And again, antenna engineering textbooks, and NEC analyses support this.

Engineering documentation references are available on request.

The FCC position for Part 15 AM users with respect to the elevated radial configurations given above is unknown -- so due care is needed by everyone wanting to try it.

Part15 AM rules may appear to be "simple," but the real science behind these systems is not.

Rich

 

[Timewarp]

Guys! Even the full power AM stations have trouble being received clearly in today's noisy
RF environment. And I'm talking about just a few miles from the transmitter.
Yes with a super radio, in a corn field, with a good ground and long wire, you might be able to hear a part 15 station miles away.
But, your next door neighor won't hear you clearly, if a tv is on, a computer is running, if he has
a power supply plugged in, a light dimmer switch, a microwave, a motor running, or numerous
other things.
The government is hearing the people and the winds of change are in the air. Those who make
an attempt will get things done while you sit here and debate how to hook up one tenth watt
into 10 feet of antenna. Wow! Wow! Bye now!

 

[Tom Wells]

Guys! Even the full power AM stations have trouble being received clearly in today's noisy
RF environment. And I'm talking about just a few miles from the transmitter.
Yes with a super radio, in a corn field, with a good ground and long wire, you might be able to hear a part 15 station miles away.
But, your next door neighor won't hear you clearly, if a tv is on, a computer is running, if he has
a power supply plugged in, a light dimmer switch, a microwave, a motor running, or numerous
other things.
The government is hearing the people and the winds of change are in the air. Those who make
an attempt will get things done while you sit here and debate how to hook up one tenth watt
into 10 feet of antenna. Wow! Wow! Bye now!

People who have chosen to create and live in an RF pigstye don't DESERVE to receive AM signals.

The FCC, having permitted, practically INVITED all the noisemakers you mention, renders itself irrelevant.

Inasmuch as the FCC does not even respect its own rules regarding pt 15, haven't the pt 15 intentional radiator rules become irrelevant?
Why should there be ANY concern over intentional radiation when properly engineered and operated, when absolutely no
concern has been given to the pt 15 unintentional radiators?

Explain why it's OK to let random RF pollution fly free, but then require intentional radiators to comply.
When was the last time you heard about a boatload of crappy light dimmers being turned away at the port because they don't in any way comply with pt 15 regs?

Every day the FCC does not address the interference they were incepted to prevent, they become more and more irrelevant.
It reminds me of the famous quote from Chicago's mayor Daley ( the father of the current mayor).
"The policeman is not there to prevent disorder; (splutter) the policeman is there to preserve disorder."
How true this seems in so many ways about the FCC.
When was the last time the FCC did anything to really help the RF environment?
I wouldn't even trust the FCC to watch my beer while I went to the restroom.

Returning to the topic of vertical monopole/radial radiation and cancellation, ... I was truly enjoying the debate over this. It's too bad we came to an impasse. Can anyone else support this position or offer another explanation for the seeming disagreement between radiation/cancellation?

___________

Hi Tom,

Buried radials reduce I^2R losses for the r-f currents induced in the earth via radiation from a nearby vertical monopole antenna system. For best radiation efficiency these r-f currents need to be returned to the transmission system.

Other things equal, more and longer buried radials will increase the tx power available for radiation by a monopole antenna system. This is the conclusion based on calculated and measured data by RCA broadcast engineers (George Brown, et al) going back to 1937, and proven by many 1000s of accurate, real-world field strength measurements with calibrated field strength meters ever since. Of course, all antenna engineering textbook and accurate NEC analyses also support this.

A vertical monopole and its complete conducting path to a true r-f ground reference (not just the short wire defined by some as the Part 15 AM "ground lead") are the only source of useful radiation from such a system. They radiate a uniform field strength in all horizontal directions, whether using 1 or 120 buried radials, or just a ground rod or two. The only difference is that a monopole system with more/longer radials will generate a greater absolute groundwave field strength at a given distance, and will do so in all compass directions (again, other things equal).

Elevated radials behave differently. Any symmetric set of 2 or more radials about 1/4-wave long each, when used at the base of a vertical MW monopole, and elevated 15 feet or so above the earth will produce about the same result as that same vertical monopole used with 120 buried radials, each about 1/4-wave long. And again, antenna engineering textbooks, and NEC analyses support this.

Engineering documentation references are available on request.

The FCC position for Part 15 AM users with respect to the elevated radial configurations given above is unknown -- so due care is needed by everyone wanting to try it.

Part15 AM rules may appear to be "simple," but the real science behind these systems is not.

Rich

Then maybe what is in contention here is just where the radials lie in relation to the true RF ground.
Most locations are somewhat less than ideal, the true RF ground is often well below the radials.
Radials in ground with good conductivity will be able to collect returning induced ground currents efficiently.
For those with less than ideal radial-to-RF ground situations, might there not be some cancellations and apparent
directionality? You do specify that symmetric counterpoise systems are omindirectional in pattern.
Does loss of symmetry result in less than omnidirectional radiation?
I do not intend to argue but am adressing the issue of why real world results often fall short of calculated results.
I have no argument with the proven results of the tried-and-true.

Wouldn't radials in less-than-ideal soils behave somewhere in between the counterpoise and perfect RF ground-and-radial systems?

 

[rfry]

Radials in ground with good conductivity will be able to collect returning induced ground currents efficiently. For those with less than ideal radial-to-RF ground situations, might there not be some cancellations and apparent directionality? ... Wouldn't radials in less-than-ideal soils behave somewhere in between the counterpoise and perfect RF ground-and-radial systems?

When the number and length of buried radials is sufficient (~120, ~1/4-wave each), then the conductivity of the earth in which they are buried is nearly insignificant. The 1937 data measured by George Brown et al of RCA was done in the sandy soil of New Jersey, with very poor earth conductivity -- about 4 mS/m. Yet with 113 buried radials each 0.41-wave long they measured groundwave field strengths 3/10 of a mile from the monopole that were within a few percent of the theoretical maximum for a perfect radiator over a perfect ground plane, for that applied power.

Buried radials never behave like elevated radials, regardless of earth conductivity -- however for certain conditions the effect each has on system performance can be the same.

Poor earth conductivity along with too few/too short buried radials increases the series loss for the r-f current flowing in the monopole. And even though the radials may all be buried in just a 180-degree sector around the vertical monopole, its radiation will still be omnidirectional (although other things equal, the radiated field will be less than when using 120 radials, each 1/4-wave long buried in a 360-degree sector).

You do specify that symmetric counterpoise systems are omnidirectional in pattern. Does loss of symmetry result in less than omnidirectional radiation?

Vertical polarization in such a system can originate only from a radiating conductor lying at least partially in the vertical plane. So if the counterpoise radials lie in the horizontal plane, then the vertically-polarized radiation from that system always will be omnidirectional, regardless of counterpoise symmetry. But far-field horizontally polarized radiation from a system with an asymmetric counterpoise no longer will cancel toward the zenith (directly above the monopole).

These comments also apply to a monopole using an asymmetric arrangement of buried radials.
//

 

[rollins]

Interference is interference. If the FCC doesn't want my household appliances to have a "good" QRM signal at some range, why would they want my Part 15 transmitter to have the same signal strength at that same range?

 

[rfry]

It was interesting to read through this old thread again — one to which I made a lot of posts, I see.

Since those days over 13 years ago I have invested in NEC4 antenna engineering software. NEC4 is capable of analyzing the performance/characteristics of antenna systems having some of its conductors buried in the Earth. The FCC accepts its results in the design and analysis even of complex antenna systems such as the directional arrays of licensed AM broadcast stations.

Below is a graphic with data generated by NEC4, showing the performance of an unlicensed AM transmit system complying with FCC §15.219.

The field intensity it can produce at horizontal distances up to ~350 feet from the transmit antenna is strong enough to overcome the r-f noise levels present at many receive locations. For very quiet (~interference-free) receive locations it may have useful reception up to a mile away.

 

[rollins]

It was interesting to read through this old thread again — one to which I made a lot of posts, I see.

Since those days over 13 years ago I have invested in NEC4 antenna engineering software. NEC4 is capable of analyzing the performance/characteristics of antenna systems having some of its conductors buried in the Earth. The FCC accepts its results in the design and analysis even of complex antenna systems such as the directional arrays of licensed AM broadcast stations.

Below is a graphic with data generated by NEC4, showing the performance of an unlicensed AM transmit system complying with FCC §15.219.

The field intensity it can produce at horizontal distances up to ~350 feet from the transmit antenna is strong enough to overcome the r-f noise levels present at many receive locations. For very quiet (~interference-free) receive locations it may have useful reception up to a mile away.

View attachment 1502

This jives with the performance I'm getting. I'm not trying to set up a "community" broadcast station, but the signal is plenty strong throughout the house. It's like FM in that it doesn't "hear" switch arcing, and the audio quality is pretty decent. This is in a semi-rural area. The range in the daytime is limited by interference from roadside power lines, and at night the range is cut in half by skywave from broadcast stations.