In this Forum I would like to describe a ground experience that has gone through several stages of improvements over time, and the interesting discoveries that have gone with it. Also, this Forum continues from two other threads: "Antenna Observation" and "Persistent or Foolish."
I won't try to say everything all at once, because if I did, this opening entry would be the size of a book. So, I will tell it like a story, part by part, over several entries, with comments welcome all along the way.
It all began before I had any kind of a home-built grounding system. There was only an AMT3000 at 1680kHz using what I call a "Wintenna."
In brief, the Wintenna is a metal window frame connected with a tapping screw on the lower inside, with a 2.5' wire down the wall to the floor and attached to the transmitter's antenna output. On the outside top of the window frame an additional length of wire rises vertically for a sum-total of 10-feet. The whole purpose of this antenna is 1.) to keep the transmitter indoors; 2.) to radiate inside and outside. But this thread is not mainly about the antenna.
The only grounding was through the audio cable, only 4-feet long over to an FM receiver, and through the transmitter's own Jumpers 2 & 3 allowing an RF ground path through the power transformer.
The problem that needed solving was that the resulting signal would not go up hill to the very rear of the yard.
A solution that got the signal up the hill was to bury a single copper wire from the transmitter up to the top of the hill, about 40-feet, attached to transmitter ground.
When RFB heard about this, he warned that the ground wire might be radiating.
In the next installment: how we prevented the ground wire from radiating.
I presented another approach to RFB and this time, if I recall clearly, he agreed, and that is the adding of an equal-lengthed ground wire on the opposite side of the transmitter ground.
I other words, now we had an 80-foot ground wire center-fed by the transmitter ground. In this way each leg of the ground wire was 180-degrees out of phase with the other, thus canceling any tendency to radiate, but still providing the counterpoise needed to get the AM signal to the top of the hill.
This same approach got mentioned again in the Forum thread titled: grounding for those without access to earth ground. Here is a pertinent clip:
Blue Sky Take 2
Submitted by Rich on June 9, 2012 - 17:07.
Carl Blare wrote: "...In essence a vertical mast in the center of the ridge, with horizontal ground plane wires of equal length going equally on both sides as far as the ridge allows, would be a possibly legal (defensible) ground plane. ... Of course having only the two radials, pointing let's say, north and south, would tend to make the overall signal directional with two lobes and two nulls."
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This may seem to be true, but in reality the only conductor producing useful far-field radiation from this configuration is the 3-meter vertical mast -- and its radiation pattern in the horizontal plane is omnidirectional (no lobes or nulls).
Based on this very minimal radial setup, we discover that ground radials must occur in even numbers so that each radial has it's equal and opposite matching partner.
But a new problem is about to enter the picture in Chapter 3.
Time to make a correction, back in the first entry of this ongoing ground experience. The transmitter in use is an AMT5000, not an AMT3000.
So we have solved two problems.
1) The ground wire all the way uphill to the rear of the yard has caused the 1680 signal to reach the distance;
2) An equal and opposite ground wire in the other direction has neutralized unwanted radiation from the ground wiring.
The length of ground wire pointing up the hill is buried under the surface of the ground.
The opposite ground wire travels through the basement, along the I-beam, all the way to the front foundation wall.
Now comes a second transmitter, an AMT3000, located at the front of the house, directly above where the other transmitter's ground wire reaches its northern limit.
In a moment of poor logic I dropped a short wire from the AMT3000 ground down the baseboard next to the phone wire and clamped it to the long ground wire that reaches to the rear of the yard.
What could be wrong with this? Stay tuned.
A copper wire 80-feet long. At the exact center point the long wire is tapped by a ground wire from an AMT5000 at 1680kHz. Down at the northern end of the long wire the ground feed from the AMT3000 at 1550kHz is attached.
It was at that exact time that I posted "Antenna Observation," which turned out to be a mistaken observation.
With no audio being modulated by the AMT5000 at 1680kHz, a fairly loud image from the AMT3000 was being heard with some distortion. I assumed that the antennas were interacting.
But the real problem was the imbalance in the ground wire, which was fixed by removing the AMT3000 from the far end.
During all this, RFB was providing guidance, and he told me I would need distinctly separate ground wires for each transmitter.
In hindsight it seems obvious that separate ground systems will fix the situation, but that leads to another very serious question, coming in Chapter Five.
This is good stuff , I am reading them and learning , thanks Carl.
Righty, Lefty. I had to say that. Thank you Mr. Gomez.
Actually, procedures similar to what I've described are mentioned in the AMT5000 Manual, p. 24, "Ground."
Also, a very common ground method is also mentioned, "You can try connecting the ground wire to the center screw on a wall outlet, a copper water pipe, etc." In other words, a connection to electrical system ground.
But since just about everything in town gets connected to electrical system ground, isn't this the same as the way in which I tied both transmitters to a single ground line? Doesn't that invite interferences coming back up the ground wire?
I'm pretty sure that using electrical system ground for transmitter grounding is a "better than nothing" approach, but having a separate ground system for each transmitter is probably better.
My little system with two radials succeeds in kicking the signal up the hill. In the next Chapter we will link to PhilB's "Ultimate Antenna" and its very serious ground radial system.
What I believe has been achieved with my matched-pair of ground radials added to a simplified antenna, is that I have increased my signal as needed to cover the property.
Imagine how much more could be done with PhilB's "Ultimate Antenna."
http://www.part15.us/node/2728
Carl,
Keep in mind that when close to an individual ground radial the field will be present. For cancellation the distance has to be large enough from them to the receiver that the fields from both ground radials reach the receiver 180 degrees out of phase and at equal amplitude. This might affect some of your observations.
You are probably going to ask what is this distance and off the top of my head I don't know for sure but it probably is going to be out in the far field at about 1 wavelength. (past both the reactive and radiative near field)
Neil
I understand your description right away, Neil, and I had not previously known about the field behavior you describe, although it makes perfect sense.
Therefore, with many ground radials, the received signal at varying distances must be many times influenced by all the near/far relationships of all those radials.
... How much more could be done with PhilB's "Ultimate Antenna."
I believe that the basic base loaded vertical is just about as dificult as most would want to indulge into myself. It's basic and not too difficult to build but tuning it is a pain! I spent many hours just "hoping" I was somewhere close to good. I used the field strength technique but every time that I moved a finger, things changed.. Very frustrating..
I attemped to get some brainstorming going on over the tuning issue from a distance and didn't get much response. I did get a little heckling from using a beer can in one of my thoughts. Maybe if I used the term "Aluminum Beverage Can" I might have received some comments or respect but that's OK. Personally, I don't see anything wrong with a little humor now and then..
With the brain power we have here among us, we could come up with the ultimate base loaded antenna that any hillbilly could construct! It may not be exactly perfect but the tuning could/would be more exact. In my eyes, this would be a far better improvment than any "magic coil" or whatever could produce..
The basic base loaded antenna is not that inefficient to worry about. Sure there are some coil losses because of resistance but I doubt that there are many on this board that has built one and played with it can say that they had it adjusted perfectly, or as perfectly as possible. I know that when my lard butt was next to it sure wasn't doing me any favors when I was tuning the thing..
I believe that most fully understand how important the grounding is. Getting a good, accurate peak on the antenna is a whole other situation. It can only be done from a distance, IMO.. And from my experience..
To extend my thoughts from the other thread, Carl..
Where the two pieces of the chicken wire crossed in the center, I bonded them in several places and connected the ground of the SStran to it. I wrapped some small gauge copper wire around the bonding points and soldered them. I used a torch but I imagine a 40 watt iron would work just as well. I just didn't have the A.C. power to run one..
Hey, 12vman, don't abandon beer can technology. I really like your can-tuner experiment, and it seems to me the only thing preventing 3-meters stacked with cans is the problem of connecting the cans electrically together.
I even save unwanted CDs (compact discs) because they have a metal base also, and although there is no practical way to attach them to anything, perhaps there is an impractical way to make an antenna of discs. Or maybe a disc ground.
I saw a solar heat collector once made from outdoor plywood, beer cans and rocks, and it made the CBS Evening News, some guy had it hooked to his roadside diner with a chain-fan to pull in the warm air when needed in the winter time.
With beer cans and concrete you can build an earth home.
First off, the base loaded 3 meter antenna has been around for a LONG time, long before anyone claimed it to be "their" ultimate antenna.
Second, many variations of that basic base loaded antenna have been done over the decades, most of which worked very well and conceived during a time when there were no CAD/NEC or other computer simulation programs. They were built by using the mind and pure labor, trial and error, success and failure.
Those who balked at your "beer can tuner" were probably already on their 2nd 12 pack anyway so don't let their double standard get in your way.
"With the brain power we have here among us, we could come up with the ultimate base loaded antenna that any hillbilly could construct! It may not be exactly perfect but the tuning could/would be more exact. In my eyes, this would be a far better improvment than any "magic coil" or whatever could produce."
There have been discussions before about a collaborative effort to design a simple but effective antenna system with remote tuning capability. I have mentioned it dozens of times that I built such an antenna system and it works. No one seemed interested so I left it at that.
In the meantime, a real world and fully functioning 3 meter remote tuned antenna system sits right outside and beyond the wall behind my monitor, doing what it was built to do and it all used common junk parts and hardware found just about anywhere. The only part I had to purchase was the gear reduced motor assembly and a PWM DC motor control card. Everything else was salvaged stuff and stuff from junk piles. It even has a remote meter indicator and sensor circuit with a voltage comparator and reference which gives it "auto-tune" capability.
Maybe someday I will publish a pdf or something about it, when there is adequate interest.
RFB
Why not center load the antenna as in the case of "Bug Catcher" type antennas. More efficient?
RFB,
I must have missed your previous mention of your remote tunable antenna or maybe I just don't remember it.
I would be interested in your writeup on this since I am now building a "permanent" outdoor antenna system. It is not known at present whether there is a need for remote or auto tuning here but your information would be a good thing to have in my library in case there is need.
Neil
.. but the PWM DC motor gizmo and that auto-tune thingie might be a little deep for most.. 😉
Did you ever ponder on a mechanical system that would be easier for most to understand? Don't get me wrong. I could follow your design but I feel if things get too complex, it could scare the bejebbers out of a novice. Something that may be simple to you and I may be deterrent to some..
I'd be interested in looking at your design. Thank you for putting so much thought into it..