The graphic linked below shows the calculated field intensities produced from zero to 5 meters above flat earth from 100 to 1000 meters from the antenna, for the other conditions shown there.
This system might be useful for areas where it is impractical or impossible to use buried conductors as an r-f ground for a vertical monopole.
Even though the two horizontal counterpoise wires used are only three meters long, each, they can provide a lower-loss r-f ground reference than many more wires/rods buried in the earth, especially if the earth at the antenna site has poor conductivity.
This antenna system has no physical connection to the earth. The transmitter was assumed to be mounted at the junction of the vertical and horizontal conductors, and powered by an on-board battery.
The system in this graphic was modeled for very poor earth conductivity — 1 mS/m, d.c. 5. But still it can produce a field of ~150 µV/m at a distance of about 0.28 miles. That field could produce useful reception by many consumer-level AM receivers.
Some study may be needed to understand this topic and graphic, but questions are welcome.
Carl Blare says
Followup Questions
Interesting presentation.
2-Questions:
2.) Is there a particular reason for mounting the assembly 1-meter above the earth? Could it be located at the earth, or, for another example, along the roof-line of an A-frame house?
3.) Would the performance improve by lengthening the ground radials, perhaps two 2X6-meters or more?
Rich says
Answers
2.) The horizontal counterpoise wires must be physically isolated from the earth itself.
If they are lying on, or buried in the earth then the currents flowing on them are produced by fields entering the earth by radiation from the vertical monopole, which currents are collected by those horizontal conductors. This process has high losses unless a large number of long radial wires is used. Broadcast stations typically use 120 x 1/4-wave buried radials, but get the same performance using only 4 x 1/4-wave horizontal wires elevated about 15′ above the earth, as a counterpoise.
When counterpoise wires are physically isolated from the earth then the current flowing on them is supplied by the r-f ground terminal of the transmitter. In effect the monopole antenna system has been converted to a balanced radiator, which needs no connection to r-f ground for efficient radiation.
For greatest groundwave fields, the system described in the NEC analysis should be installed fairly close to the surface of the earth. Heights of 20 or 30 feet should not cause big problems, as long as that antenna system is the sole source of radiation (no long “ground” wires used, including grounding via an a-c outlet).
3.) The field strength it radiates might rise slightly, as the longer elevated horizontal conductors used as a counterpoise might reduce the capacitive reactance at the feedpoint — which means that r-f loss in the loading coil might drop by a few ohms.
Carl Blare says
Not a Minor Matter
Rich, I think this presentation is not a small or slight alternative method for designing a Part 15 AM antenna, it might even be what those who talk about “elevated antennas” might actually be looking for.
And of course, you’ve already said that earth-ground limitations might prohibit actual buried radials, in which case this design would “solve the problem.”
With the ground radials mounted about 1-meter above ground, per your original example, it would be like having a “roped off area,” a sort of “fence” made out of radial wire for a total length of 20-feet. Perhaps it could be made part of an actual wooden fence, which would neatly put the antenna right on the edge of a property.
Rich says
Another Possible Benefit for This Configuration…
… is that it should stabilize the tuning of the system, as the loss in the r-f ground reference when using the elevated counterpoise essentially will be independent of the moisture in the earth around the antenna site.
Carl Blare says
Incorporating the Idea
This antenna approach for Part 15 AM is more than academically appealing to me, I already am beginning to visualize actually implementing it.
By coincidence, I’ve been clearing a fair amount of yard-space for purposes of building an “Ultenna,” the full-scale vertical pole with plenty of buried radials as described by PhilB, and that project is moving along.
But there’s also room for a “Raised Radial,” an antenna such as described here by Rich.
The weather is nice today. I will stand around out there considering where to put this new type of antenna.
What other ideas might you have?
Rich says
A Caveat
“But there’s also room for a “Raised Radial,” an antenna such as described here by Rich.”
If they are going to be using the same or close frequencies, suggest that they don’t operate at the same time and are kept apart as far as physically possible, to minimize their effects on each other.
Carl Blare says
Agreed
I agree with that advice.
In fact, I thought they would both be on the same frequency, for alternate use, one being a back-up for the other.
The other advantage of both being on the same frequency is that they can be compared, one at a time, to measure the respective performances.
PhilB says
What about the other ground paths?
“This antenna system has no physical connection to the earth. The transmitter was assumed to be mounted at the junction of the vertical and horizontal conductors, and powered by an on-board battery”.
This brings up the same old issue concerning ground connections that has endlessly been discussed related to any type of elevated antenna. Powering the elevated transmitter from an on-board battery doesn’t isolate it from ground. There are still the persistent problems of how to connect the audio feed without introducing an RF path to ground and how to provide lightning surge protection without running a ground wire up to the transmitter. Powering the transmitter form an on-board battery is totally impractical.
In lieu of battery power, it is possible to isolate the power wires for RF by placing RF chokes of 1mH or higher in series with both legs of the power feed at the transmitter.
The audio cable, whether balanced or unbalanced, will present a low RF impedance to ground. The impedance is unpredictable, but it will certainly have a major effect on the antenna. High value chokes, on the order of 1mH or higher, in series with the audio wires at the transmitter will isolate the RF path to ground, but may have an adverse affect on quality of the audio feed.
The lightning safety ground, which all would agree is a requirement, presents a few problems which could be solved by a gas discharge surge suppressor connected at the transmitter between the ground terminal and a wire to a ground rod. Or, as some have suggested, an RF choke in-line with a ground wire located at the transmitter. The choke would need to be 1mH or more to be effective for RF ground isolation. A 1mH choke wound with heavy wire would be huge, so that’s not really viable.
The BOTTOM LINE here is how the FCC will judge any sort of elevated antenna, even one with an elevated counterpoise. My take is they will judge any elevated antenna to violate the rules because they will assume it has the other typical ancillary paths to ground, which are a violation of the ground length part of the rule.
If anyone actually does all the RF isolation for all the ancillary ground paths, they will need to be prepared to provide a technical explanation of everything they have implemented to isolate the RF paths. I think all of us would dearly value hearing of such an experience with the FCC. Please share it!
By the way, all of the ancillary wire RF isolation mentioned above does NOT apply to simple elevated vertical antennas without any sort of elevated counterpoise. Isolating ALL ground paths for a simple elevated transmitter/antenna will cause the antenna to FAIL COMPLETELY.
Carl Blare says
Not Solutions
The audio path to the Rich Design elevated AM antenna/radials can be achieved by using a wireless link, with an FM or Auxiliary Frequency Receiver located within inches of the transmitter, however the receiver requires its own antenna, which will impose a reaction in the AM field.
The battery supply might be part of a solar collector mounted at the top of the 10′ pole, but getting the collected voltage down to the transmitter receiver would place wires parallel to the antenna, another disturbance of the AM field. Assuming the 10′ antenna was hollow, the power wires could be hidden inside the antenna, but surely would still interact.
In any case, these offer alternate methods of trying to reduce the AM transmitter system to a minimum of parts.
Carl Blare says
Why Not This?
How To Make Rich’s Groundless Antenna Work.
An Engineering Proposal by Carl Blare.
Bulid the antenna per Rich’s original design, but with the following modifications.
1.) The two horizontal 10′ radial wires would each be shielded cable with two inner conductors;
2.) The shields of the two radial cables would serve as the ground radials attached to transmitter ground;
3.) The inner two conductors of one cable would carry both audio and power – A.) Audio 600-ohm balanced,
B.) Phantom power superimposed on audio wires, decoupled at far end by appropriate inductors.
4.) The second radial cable would have its two inner conductors terminated at both ends with 600-ohm resistors to make it equivalent to cable 1.
5.) The feed point at the extremity of cable 1 will be a PVC pipe dropping directly into the earth and connected underground to the nearby building. To maintain equalibrium the extremity of cable 2 will have a dummy drop into the ground but no connection to the building.
A small reception in celebration of this invention will be held during the extra hour at the two 1 AM’s.
MrNaturalAZ says
15.221b compliance?
While elevated radials are a great idea from a technological and performance viewpoint, would such a system withstand FCC scrutiny? From Title 47 Part 15.221:
“(b) The total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters.”
You propose a pair of 3m radials. Surely the FCC will perceive them as either part of the “antenna” or “ground lead” thereby instantly rendering the station non-compliant. No?
Rich says
Part 15 AM Counterpoise
“You propose a pair of 3m radials. Surely the FCC will perceive them as either part of the “antenna” or “ground lead” thereby instantly rendering the station non-compliant. No?”
Maybe so. But the applicable FCC paragraph is 15.219.
That is why the NEC graphic I posted includes this text:
Compliance with FCC §15.219 = ?
Those two, in-line horizontal radials produce no useful radiation, because equal currents are flowing in opposite directions at each instant of time, and their far-fields cancel each other.
They aren’t really “ground leads,” because neither of them connects to a physical r-f ground in the earth.
Some FCC field inspectors might recognize this, and some might not. The operator of that unlicensed system would have to take the initiative to work through this issue with the FCC, if a citation was issued based on their use.
PhilB says
Still have a ground problem
Rich, you are speculating on just the legality of the elevated ground radials. The point about the radials not radiating is accepted, but it’s not that simple. There are still other paths to ground. Carl proposed a way to solar-power the transmitter and hide the audio feed wires. Even though the audio wires are hidden, they still provide an RF path to ground through the audio source. It would be difficult to completely isolate the audio source from RF ground while maintaining a clean, noise free audio signal.
Even with a hypothetically completely RF isolated audio feed, the wires up to the transmitter would disturb the parameters of the proposed ideal elevated antenna with elevated radials.
Another proposal, feeding off of Carl’s, would be to implement an STL receiver collocated with the transmitter and also solar powered. The solar panel powering both the transmitter and STL receiver would be located adjacent to the transmitter at the same level as the radials so as to absolutely minimize the length of wire to the transmitter/STL. A solar panel also implies a battery to cover cloudy and nighttime periods. A small lithium ion battery pack could be collocated with the transmitter/STL/solar panel.
So, the bottom line is: will the FCC accept the elevated radial antenna and is all the above really practical? The small performance increase realized compared to a ground-mounted antenna with a good radial system doesn’t seem to warrant the complexity.
The NOUOs that provide any information pertaining to antenna height say something like “the antenna was observed to be 20 ft. high which is in violation of the 3 meter rule”. After such a drive-by judgment, the victim would need to provide a ton of technical documentation in an attempt to validate that the system really does comply with the 3 meter rule.
Rich says
Ground Problem
“So, the bottom line is: will the FCC accept the elevated radial antenna and is all the above really practical? The small performance increase realized compared to a ground-mounted antenna with a good radial system doesn’t seem to warrant the complexity.”
There are such issues, for sure, however this configuration was suggested for sites where a ground-mounted antenna using buried radials was impossible, or at least, impractical — rather than as a means to provide a performance increase.
It could be a useful option for such circumstances, if those issues were resolved to the satisfaction of the FCC.
Carl Blare says
Fence Sitter
The “RichMitter” above-ground antenna idea is in my plans, as said earlier, because it has certain appeals.
Besides being an alternative for curcumstances when ground space is unavailable, I see it as excellent for placement on a wooden fence right on the property line, or up on the roof-line atop an A-frame house.
In my forthcoming test installation of this antenna design the power and audio will arrive buried in shallow earth, climp the fence inside a lead pipe right at the center-most junction of the radials.
Why lead (pronounced “led”)? Lead is the most shielding metal against the passage of RF waves. Everything should be fine.
Rich says
Lead Us Not into Temptation
‘Why lead (pronounced “led”)? Lead is the most shielding metal against the passage of RF waves.’
Actually the resistivity of lead is only one order of magnitude worse than copper.
ρ (Ω·m) at 20 °C:
Copper 1.68×10^-8
Lead 2.2×10^-7
But lead is used as shield for x-rays and gamma rays due to its high density and high atomic number.
Carl Blare says
Can’t Be Stopped
Not even the inventor of the “RichMitter” above-ground antenna can stop me from building one.
I may not use lead, however.
Nate Crime says
Reply to #10
So the system would look like an inverted letter ‘T’ I can see how any wires for power and audio connected to the transmitter case would add an extra parasitic ground and mess up the concept as presented.
I have a few ideas to propose.
For an all-in-one transmitter with attached antenna and using a single cable for power and audio, you could add the ten foot radial wires clamped to the case. Now, take some ferrite blocks as used on wires for noise suppression, and wrap the cable through them right where it goes into the transmitter. You might be able to use a string of ferrite toroids in the same position too.
It’s a method that hams use to stop RF from traveling down the outside of a coax feed to an antenna, for example a Dipole, and messing up the antenna’s pattern, or having RF go down the line into the ham’s radio shack and cause havock. With enough ferrite, the resistance at your frequency should be high, and not allow the line to act as a significent ground.
Idea 2, for low impedance RF out, such as the Talking House F-connector and other transmitters, which would have the loading coil in the antenna, how about feeding the RF output through a transformer to the feedpoint at the base of the coil, so that the connection is inductive, and there’s not direct ground to the antenna system itself?
Rich says
About Reply #18
… For an all-in-one transmitter with attached antenna and using a single cable for power and audio, you could add the ten foot radial wires clamped to the case. Now, take some ferrite blocks as used on wires for noise suppression, and wrap the cable through them right where it goes into the transmitter. … With enough ferrite, the resistance at your frequency should be high, and not allow the line to act as a significent ground. …
If due to ferrite blocks wherever located, such radial wires used in an elevated counterpoise cannot conduct r-f current along their physical lengths, then their usefulness with a monopole radiator is ~zero.
… how about feeding the RF output through a transformer to the feedpoint at the base of the coil, so that the connection is inductive, and there’s not direct ground to the antenna system … ?
1) The loading coil, by itself, can produce the inductive reactance needed to offset (resonate) the capacitive reactance of a 3-m, vertical, MW monopole.
2) For about equal radiation efficiency, both of those configurations need to be driven against a ground connection having about equal r-f loss.
Nate Crime says
Hi Rich, I was thinking of
Hi Rich, I was thinking of putting the ferrite choke only on the audio and power leads, and have everything else as you detailed it with the battery powered transmitter you proposed. With some of the transmitters, it might be easy to try because they use a single cable with audio and power both on it.
The link idea would just put the break on the antenna side of the transmitter instead, just a coupling coil through low loss ferrite to the low impedance feed point on the antenna system, as you previously described, trying to reduce the inverted T’s connections to ground.
It seems like an alternative approach and needs some testing.