i read plenty of old tech books and what i remember is that once you go past 36 radials its diminishing returns. the radials act as a ground plane for the antenna and thus behave as part of the antenna. ground rods dont do this. i did however see some benefit to dropping a ground wire down an unused sprinkler well.
All this talk about radials has me wondering (again).
As you all may know I have an elevated Procaster that's been on the air nearly 4 years now. I run it with no ground connected at all, due to the limitations on ground lead length (even if I didn't have an antenna at all, I'd still be over the limit on the ground lead alone).
But I have from time to time wondered about elevated radials.
I have seen reference, over the past few years, to the concept of elevated radials, either connected to the transmitter ground itself, or the suggestion that a roof mounted transmitter with the ground lead being a short wire connected to a metal roof would be both effective and legal. This would imply that connecting the ground lug to my metal gutters would create a legal, horizontal, ground plane of sorts. It would be interesting to try it and see what field strength changes to. But would it be legal?
Whether of not this would greatly benefit my operation, I don't know as I cover my small town just fine. It doesn't take much, in an area with a very low noise floor, to cover 4 blocks wide and 1/4 mile long, when I'm in the middle of it!
My curiosity more leads to legality. We all like to believe that horizontal radials don't radiate, and are thus legal. The ARE they? I don't believe there's any documentation or inspection paperwork, showing that a transmitter with a 3 meter antenna and horizontal ground leads will meet the legal requirements of antenna + ground lead equaling no more than 3 meters. I'm suspecting that the length of all the elevated radials combined would wind up gounting as "ground lead". I would not try this unless I had some hard evidence that it would be considered legal. As you may know I try to run my operation as blatantly legal as possible.
Anyone have any hard evidence on legality of elevated radials, etc?
TIB
Well, if you want to be picky, there's no hard legal evidence that attaching a short ground wire to a long metal mast is not OK. Nowhere in the rules does it state that a ground can't radiate. And in fact, FCC inspectors used to interpret the rules reasonably strictly, allowing short ground wires to large metal objects. That has obviously changed in recent years.
IF, and it is a big if, the intent of the FCC is to not have a long radiating ground, then elevated radials should be OK, as long as they are 180 degrees apart, strictly perpendicular to the antenna, and each the same length. You'll get no radiation, just an increase in antenna efficiency.
If those radials are sloped, however, you will get a marked increase in radiation.
The FCC inspector has the final say. I'm not sure that you'd know for sure until an installation that had similar radials was inspected, and passed.
I have recently gone in print to debunk the notion of "long ground lead".
It seems obvious and logical that a vertical wire below a transmitter that has a vertical antenna above the same transmitter is not a ground lead but is in fact the negative leg of a vertical dipole antenna. As soon as the sum total of vertical antenna wires above and below the transmitter exceeds 3-meters it is not FCC compliant.
Calling it a "ground lead" is erroneous.
Horizontal radials are not "ground leads" either, so long as each radial is matched by an equal length radial in the opossite direction putting the two radials out of phase with each other.
I strongly propose that radials must exist in opossing pairs so as to null-out any possible radiation by being out of phase with each other. Only even-numbers of radials meet this standard.
Because bonafide radials are not "ground leads" they are in fact ground itself... made more obvious if melded with the earth, but when elevated above the earth would be known as "virtual ground".
I have not encountered any FCC documentation either supporting or otherwise discussing these principles.
That's a good point Carl. And so is Artisians.
If you want to be 100% by the book you would have a 2 foot antenna and 3 ground plane radials. in essence what you would have would be the equivalent to a CB ground plane.
The point is that there is no 'book' describing radials, elevated grounds that don't radiate, etc.
You're entirely at the discretion of the FCC inspector.
And this is exactly why I've never tried it or experimented with elevated radials. My goal is to always be blatantly legal. Which is why I was wondering if there was any precedent for elevated radials.
I don't really experiment at all with my station, as it's been on 24-7 for almost 4 years and I actually have regular listeners. I don't want to screw with it when people are listening. Experimentation would require a second transmitter on a different frequency.
TIB
Beyond what the rules say in the literal sense I suggest that "discretion" is not always dangerous if solid physics are on your side.
All of us seem to agree that wires that radiate are necessarilly measured by the meter and anything that doesn't radiate can be called by any name you prefer, e.g., "ground lead" "negative leg of dipole" "virtual ground" and literally is a matter of REASONABLE discretion.
Radials that don't radiate are safe territory in the realm of logic, the thing to fear is an agent who acts unreasonably, for whatever reason.
Planning our lives based on fear of what rogue officials might do is akin to paranoia.
The problem is usually because our gound leads do radiate due to our short antennas. The FCC has never been very clear regarding the use of top hat capacitance but I swear I've seen them tag elevated radials. You essentially turn the setup into one large dipole antenna which would count towards total antenna length. Tim has about 2 feet of wire he could play with, I'd venture to guess that 2 feet of dangling wire on the end of his procaster might actually help out that signal just a touch.
do not radiaite even with an electrically short antenna.
problem is all the radials must be the same legth and have another radial 180 out of phase with the other and they can't droop must be perfectly horizontal.
this is not easy to acheive in an elevated install but not impossible.
an example would be such a radial system laid out on a flat city building or apartment building roof.
Tim
if you have the clearance inside your attic for the 3m whip then placing the procaster inside over a symetrical ground plane laid out on your attic floor would be legal as it should not radiiate in this case and they would be perfectly horizontal. but you must take great care to make the radials symetrical.
as long as you have a shingle roof (no slate or aluminum) with wood sides it will not hamper your signal any.
Part15 Engineer said: "problem is all the radials must be the same length and have another radial 180 out of phase with the other and they can't droop must be perfectly horizontal."
That got me to thinking about radials on the earth.
The earth is not level in all places, so radials might end up not being perfectly horizontal.
In fact Jim Henry reported a finding that I also noticed, being on the side of a hill the upward pointing radials actually push the signal uphill and over the crest of the hill to the area beyond.
The other problem, keeping radials exactly straight in the air has got to be a difficult physical task with wind blowing and birds landing.
I can relate to the discussions of imperfect terrain.
I have yet to get an antenna designed for my Chris Cuff C-Quam Stereo Transmitter.
My yard is mostly ledge rock, with top soil placed on top of it. Those ledge rocks stick up in a lot of places. I can't very well place a 10 foot antenna in the middle of the yard, because I rent and have other tenants who use the yard.
Although I could go ahead and do an install in the middle of the back yard, I think that is impratical for the others who live here.
I have trees in the back yard, a little piece of land that is still uncleared of trees and wild brush (wooded area), but those trees are so close together, they are basically catapults sticking up in the air. They sway something terrible in the wind. I can't imagine even placing a wire onto one of them, the trees would sway to the point that the wire would be pulled and loosened over and over again, also it's impossible even to get a wire up to the point where the trees have branches. Like I said those trees are basically sticks sticking 50 feet up with branches and leaves way up at the top portion.
I have one lone tree in the yard, that has potential, it has grown quite tall, however it has many branches and leaves and if I am not mistaken, those act as negative deterants to the signal.
I suppose I could place a long pole below the antenna to get the actual antenna above the highest branches, but then we have another issue with an antenna swaying in the breeze, even worse if there is a lot of wind.
I am on a hill, with a slightly inclining and declining terrain running west to east, so basically I am on the side of a hill at an elevation of 156 feet according to Google Earth the highest point to the west is 175 feet. Then of course you have to factor in trees and buildings surrounding my house and the highest hill is to my east which is 190 feet and is roughly 0.08 miles from my house, to add insult to injury, there are 3 story apartment buildings lined up along this long hillside.
Soooo, my project continues to remain on hold as I ponder and ponder and ponder what is the best way to go. I could go with a roof install on the smoke stack, but I currently have UHF television antennas on that for OTA TV and a scanner antenna mounted above those.
This antenna lengh restriction of 10 feet also make it difficult to simply string a wire horizontally from tree to tree out of the equasion, since the wire length would end up being over 10 feet.
So, I am faced with two obsticles, ledge rock and no place reasonable to place a ground mounted antenna.
Ponder...ponder...ponder...ponder....
To Be Continued..........
Bruce.
This posting is inspired by the recent post from Mr. Bruce
With the question of "imperfect terrain" I have already decided that my earlier impression of AM antenna locations is inaccurate.
Like many radio buffs, which means radio lovers undressed, what I think I see standing as I do on the earth, may not be any kind of an accurate representation.
Land slopes upward, downward, there are crests and nulls in land distribution but viewing it from ground-level is not accurate. Everything is "downward" from our gaze because we stand around 5-feet tall. "Uphill" might appear to simply "meld into the distance" where the trees are tall.
Beethoven understood this when he wrote his string quartet Opus 130.
And when you think about it, we are condemned for infinity to come always to ground and length because they are central to part 15, unlike the problem of Trump, which opens concerns of White Nationalism, racism, criminal hate and program content.
That is why I think the earth is not flat and Aijet Pai is wrong.