Remember when cars had a real metal antenna on the fender? The actual antenna is the r.f. radiator and the fender is the ground. (Thinkin' in reverse.. txin' and not rxin') The ground is the other half of the antenna. Them rf's flow from the antenna and are collected by the ground to make a complete circuit. If ya have a poor ground, the circuit is gonna be poor. The earth is a poor conductor to them r.f.'s, usually. A metal fender is fantastic!
In our game, we wanna get a good, conductive ground area around the base of the antenna the best way we can. Those r.f.'s are lookin' for a place to go and we wanna oblige them the best way we can. The better route we provide for them to complete the circuit, the better they're gonna work for us..
Have ya ever seen one of those "Breakerbreakercom'onback" C.B groundplane antenna? It has an element stickin' straight up and 4 elements stickin' out of the base, at the mount. The one stickin' straight up is the radiator and the 4 thingies stickin' out horizontally from the base is the groundplane area. Them r.f.'s flow from the straight up element and flow to the 4 at the base to complete a circuit. This is the same thing that we are tryin' to do with a ground mounted set-up..
We have this thing called resonance. This is achieved by the length of the radiator and the workin' frequency. (A whole other story) The ground isn't as important as the radiator BUT ya need both to make things get into sync. The ground is just a return but ya need it to make things happen. The more ya return, the better the efficiency of the circuit! Better efficiency, more of those r.f.s can get launched into the air!
Kinda reminds me of a baseball game. The batter hits the ball. The outfielders catch the ball and throws it back to home plate.. The crowd roars..
12Vman you explained it like I never heard it explained before.
Let me see if I can repeat what I just learned.
First, there is a pitcher. O.K. He pitches the ball. Then there is a batter. He bats the ball.
I get it. Finally. Part 15 is so beautiful I wish it was big enough to kiss.
Ok, having played with 27mhz, 2.4 ghz, 5 ghz, 900 mhz, and now thinking about 1.5 mhz, I look at the drawings and with my severely limited RF understanding, I start thinking about this and I get a little lost.
First, the radiating element IS the whip at the top. There is zero potential voltage from anywhere on the coax and ground wire to the point where the soil touches any part of the ground rod. So, if there is additional radiation from the coax, it is due to ... The resistance of the soil, allowing the shield of the coax to then rise above "earth" potential, that being a big, fat, zero, for all in tents and porpoises.
So, logic says that if we improve the earth ground - with a very deep, very moist, very widespread earth ground that really, REALLY pulls our coax to "earth" potential, that being zero, we'll reduce emissions. But the real world says that's untrue, and we'll gain signal and range by improving earth ground.
At this point, I'm confussed.
Or cornfuzed, or whatever the heck it is.
My thoughts are, that field strength is increased, due to the fact that the radiator is actually farther from earth, and this matters because of the very long wavelength we're dealing with, and that the proximity of earth and the very long length of the wave results in a wave conducted into the ground, rather than free or open space. If we could raise this thing to a full wavelength above ground ( wow, what a tower!), we'd have rather amazing range and signal strength for a flea power transmitter, and it's NOT being radiated by the earth potential tower, merely not being shorted to ground because of the long wavelength.
Am I anywhere near reasonable, here?
If we were to take one of these things and put it on the roof of our apartment, which just happens to be the top floor of a 15 story building, attached nicely to the roof and huge network of well grounded plumbing, I'd say that we're going to have higher level of propagation... Than if we didn't.
But nobody here is going to make the mistake of saying that somehow we increased the power.
Such is the foibles of using a regulatory framework designed to prevent interference from unintentional radiators as a means of regulating intentional radiation....
And thus, we have a gazillion devices under Part 15, with a whole set of rules that evolve, have uneven and inconsistent enforcement. Yet, nobody at the FCC (that I can tell) has yet to get the brain spark to say "hey, let's create a new Part 15 with the notion of ENABLING the use of spectrum as much as possible, and so let's change our practices and procedures to reflect the goal of use, rather than prevention..."
So there's not really enough part 15 broadcasters to forge a coalition with enough resources to lobby the FCC to do this. Sad that it takes more than one person with a really good argument, but it does. They're resistant to change, and more resistant to crossing the guys who keep the Congresscritter's campaigns filled with money... Though they're ostensibly there to serve like the employees of the public they are.
So, I'm wondering if anyone could possibly get someone at the FCC to actually listen and agree to enable both am and fm unlicensed, purposefully and intentionally? Is there some other industry group that would ally for the same purpose?
All the other users of AM and FM don't want us, as we're competition. Which is precisely what the FCC is supposed to PROMOTE, not prevent.
First, the radiating element IS the whip at the top. There is zero potential voltage from anywhere on the coax and ground wire to the point where the soil touches any part of the ground rod. ... If we could raise this thing to a full wavelength above ground ( wow, what a tower!), we'd have rather amazing range and signal strength for a flea power transmitter, and it's NOT being radiated by the earth potential tower, merely not being shorted to ground because of the long wavelength.
A vertical conductor above the earth connected to a conductor or conductors buried in the earth has close to zero potential and resistance for the passage of direct current to and from the earth, but not so for alternating current, e.g., radio frequencies.
When radio-frequency current travels along a vertical, so-called "ground" conductor above the earth, additional a-c resistance results from the coupling of that conductor with space. That coupling results in radiation of a radio wave, whose field intensity is a function of the length of that conductor above the earth, and the amount of r-f current flowing along it.
That is the reason for the increased performance of Part 15 AM systems using elevated mounts together with a relatively long conductor to the earth as a "safety" ground.
How about 18 feet up rich ?
The earlier post about AC/DC grounds was made at around the time you were posting about a system at 18 feet, and gives the general answer. That height would not produce as much field as the 33-ft height in my NEC model, but it would still be a few times greater than if the system was mounted just above the surface of the earth (other things equal).
If I recall... for the 22 page field agent manual, there is a paragraph stating the field agent must determine if a system is operating under one sub part or the other.. specifically it states 15.209 or 15.219, and each one's own sub parts below that.
The FCC certification issued for Part 15 AM transmitters does not specify certification for use under either §15.209 or §15.219.
The document only states "Part 15C" under the column "FCC Rule Parts." Part 15C applies to intentional radiators, and includes both .209 and .219.
"Earth Ground" and "Antenna Circuit Ground" are two different animals. The earth ground is for safety. Lightning and general static caused by wind and stuff needs to be removed from the antenna or it will find a path by itself. You don't want it goin' back through yer equipment! We provide a path with a ground rod or water pipes..
Antenna circuit ground is necessary to make a complete circuit. The earth is a poor conductor for them r.f.'s to flow. We attempt to make a better circuit by poundin' a ground rod into the earth but them r.f.'s don't have a shovel to dig their way to the ground rod! Some of the stronger ones make it through but most of 'um just get sucked up and go nowhere. This is why we put wires around the base of the antenna to get those r.f.'s back to the antenna as much as we can..
We attempt to "use" the earth for the antenna circuit ground because of the wavelength of the frequencies that we are messin' with. A good antenna ground requires a lot of long wire(s) and we ain't rich! (no pun intended) We try to cheat and most of the time we get enough to make things work somewhat. This is why the antenna ground area is important..
As for coax.. Think of it as a one-way highway. When traffic is flowin' good, everyone's happy and goin' to where they are headed. When someone screws up and causes a traffic jam, folks start yellin', horns start beepin' and the highway flow stops but the flow of traffic from the other roads feedin' the highway never stops comin'. Folks start usin' back alleys and other ways to get to where they're goin'..
If the coax is loaded the same on both ends, none of those r.f's should leave. If the load is changed at one end, r.f.'s get backed up and the flow doesn't stop. They will find another route to get to where they are intended to go. Them r.f.'s will jump ship and go everywhere! The shield will become a radiator!
Carl.. I forgots the pitcher! That's the transmitter.. LOL
"Earth Ground" and "Antenna Circuit Ground" are two different animals. The earth ground is for safety. Lightning and general static caused by wind and stuff needs to be removed from the antenna or it will find a path by itself. ... Antenna circuit ground is necessary to make a complete circuit.
However a single conductor running from an elevated transmitter or ATU to a ground rod that is intended to be a lightning (safety) ground also will radiate the station's signal, for the reasons given in my post earlier this morning.
The r-f field produced by radiation from that safety ground wire can be improved by installing horizontal, buried radials directly under the vertical ground wire leading up to an elevated transmitter/ATU+whip, and connecting the common point of those radials to the ground rod.
"The FCC certification issued for Part 15 AM transmitters does not specify certification for use under either §15.209 or §15.219."
Not in the field manual, but in owners manuals and web sites and install manuals they do say what their device is certified under.
"The document only states "Part 15C" under the column "FCC Rule Parts." Part 15C applies to intentional radiators, and includes both .209 and .219."
Exactly...and is why the field manual states the agent must determine if the system is compliant under 209 or 219.
I wont debate what is clearly written on the field manual. It's interpretation is quite simple and straight forward. Your either compliant under 209, or 219. If the system falls into another catagory, such as 221, then it has to comply under 221 and 209.
Only the inspecting agent can determine compliance under any of those parts. As the manual clearly states, its up to the agent to determine the compliance and under what part said system is in compliance or not.
Pointing out a point made in a blog, Part 15 is the only set of rules in the entire mess that has varying interpretation angles while Part 73 or 79 or any other are quite specific with no room for all this interpretation.
Now why is that eh?
It's as on one angle your ok, but at another angle your out of compliance..all based on interpretation not absolute rule.
For some thing so simplistic as 3 meter antennas and flea power, the rules sure are set up to make it far more complex and complicated than it need be.
RFB
If you had the means and freedom to design your own part 15 broadcast SYSTEM, what it would be, and what would the environment be?
Antenna design, location, grounding, physical location characteristics, and so on?
A vertical conductor above the earth connected to a conductor or conductors buried in the earth has close to zero potential and resistance for the passage of direct current to and from the earth, but not so for alternating current, e.g., radio frequencies.
At what frequency range does this effect become signficant?
At what frequency range does this effect become significant?
Well below the AM broadcast band.
Elevating a 1700 kHz Part 15 AM transmitter with attached 3-m whip 20 feet above the earth, and connecting the r-f ground terminal of the transmitter to a 20-ft conductor connected to an earth ground results in a system radiation resistance of about 2.75 ohms.
The radiation resistance of that transmitter+whip mounted a few inches above the earth, using a very short ground conductor to the earth is about 0.14 ohms.
The resistance of each of those radiating conductor lengths to direct current is much less than 1/1000th of an ohm.
I'm not sure this simulation adds anything to the discussion.
We already have the case where elevated antennas have been disallowed, primarily because of the long ground wire. Even if you have a short ground wire attached to a mast, that is considered essentially a long ground wire. And those long ground wires radiate.
I would assume - please correct me if I'm wrong - that it is the long ground wire in the simulations for an elevated mount that are causing the stronger field intensity. And we've been down that route before (talk about being 'repetitive').
Whether you're feeding a transmitter such as the Hamilton Rangemaster with CAT-5 (audio & power) and it is mounted high, or whether you are feeding a Talking House with an ATU mounted high with coax, the situation is the same. Long ground wires, with the FCC (at least currently), may be a problem.
The solution: don't have a long ground wire (duh!). The Talking House with an elevated ATU can perform adequately without a ground wire (particularly if you use the supplied power supply, which uses the AC neutral as a ground) - I could get mine to peak at 6 on a meter calibrated to 10. When I added a short ground wire, it rose to slightly over 9. But a 6 means that the signal was getting out. It would be up to the individual installer whether an elevated ATU or Hamilton or whatever without a ground wire that is not being obstructed is preferable over the same units mounted closer to the ground with a short ground wire.