What "Rich" is saying, is that everything has been done, now it's time to accept the past as the one and only reality.
Carl, IMO that is an incorrect assessment of my post, but certainly you are entitled to it.
Many experiments have been made on the use of buried wires with monopoles, even back in the 1930s. It seems prudent to research this, and learn from it as a way of understanding the subject better -- which can lead to more focused (and unduplicated) experiments by anyone now wishing to do so.
He just repeated himself.
I believe having 'sloped' radials under ground will have no benefit, i.e., time and energy would be better spent on other things.
We know the benefits of very-long-time real-world implementation of ground radials, flat, buried a few inches underground, with adequate bonding to ground rods (generally, the deeper the better) at the base and outboard. As well, there are charts showing return path conductivity with both the number and length, which gives us good information to help decide where significant diminishing returns occur.
Where Earth ground is not available ... the latest thread shows some promise, but there are yet other things. Electronic synthesized ground hardware, Isotron-type tank antennas, cage monopoles for synthesizing increased 'skin effect', etc.
I experimented with this idea years ago on my uncle's ranch and used 8 10 foot long radials slanted at about a 10 degree angle from the center. Fortunately the setup was located in a fairly large hole or indent on the surface which was about 40 foot diameter. It was a simple matter of placing the radials and using rocks and wood to support the radials as the fill in dirt was placed into the hole.
The slanted radials really did not improve the field strength significantly over horizontal radials buried in the dirt.
One thing I did notice that improved was the sharpness of the tuning and it's reactance to external influences by induction. This shows that the more ground area (footprint) created makes the antenna system perform better, but tuning it is a headache as being within 4 feet of the puppy hut and radiator would throw off the resonance. At that point I made a remote controlled tuning mechanism which helped out a lot.
RFB
"...tuning it is a headache as being within 4 feet of the puppy hut and radiator would throw off the resonance. At that point I made a remote controlled tuning mechanism which helped out a lot."
Can you elaborate a bit on how this was done? I designed several systems for remote tuning, but the only ones I figured would work were hand-operated ones made from wood or plastic. Motor driven hardware designs seem like they will generate interference, and conduct as well, in the return field, thus giving false resonance peaks.
Sometimes I wish I had a small CNC milling machine. I could implement my design(s) with PTFE parts, no significant conductivity.
"Can you elaborate a bit on how this was done?"
I used a combination of gear reduced motorized units with small pulleys and various surplus tape deck (reel to reel) belts. The tuning cap, consisting of an old air cap tuning block (double blade). Those always had the nice large pulley where the tuning indicator needle would tie via a spring loaded nylon string to keep the tension correct. Same setup with the remote control system powered and controlled with a PWM circuit to work the DC motor. The motor/gear reduction unit is wrapped in aluminum foil and the foil connected to ground for shielding. .1uf ceramic caps across the motor power leads and ground to shunt any motor brush noise. PWM circuit uses a potentiometer to adjust the gear box rotation to left or right. A position calibrate potentiometer is glued to the back side shaft of the air tuning cap and drives an op amp with a reference voltage and a variable voltage to drive a meter to indicate the tuning cap's position. Meter face is a simple readout of numbers from 0 to 10 maximum scale. Center of meter scale is center of rotation of the air variable cap.
Some scrap multi-wire cable for control signals and meter indications which included the tuning position meter and an RF sensing circuit at the antenna sampling by induction the resonance of the antenna.
Later I added a peak sensing circuit and now the thing will adjust itself for maximum resonance constantly. This system serves as my CC's backup.
RFB
Glintch post
Perhaps I missed something, but where did this 1 mile theoretical limit for Part 15 AM come from? It seems to me that there are a lot of assumptions buried in that one statement - what is that 'typical' Part 15 setup, what is a 'useful' signal and even what is at the receiving end?
Perhaps I missed something, but where did this 1 mile theoretical limit for Part 15 AM come from?
Good question. The link below shows the details.
Note that 50 mW of Z-matched power at the feedpoint of a Part 15 AM antenna probably is on the high side, and that zero ohms in the r-f ground connection definitely is on the low (impossible) side.
But even so, the groundwave field at 1610 meters (about 1 mile) is not quite 150 microvolts/meter, which is about the minimum needed for fairly noise-free reception on a boombox, Walkman or other consumer-grade AM receiver inside a home in an urban area.
We're getting a bit off topic in this thread, and the range estimate you provided makes sense if you assume that the receiver is a consumer grade radio. But NOT if you have a good car radio with decent sensitivity and selectivity - there, the useable range can be much greater.
Here's a link from this Forum, http://www.part15.us/node/952 that discusses legal Part 15 AM useable range in some detail. It pretty much matches what I've seen with my Rangemaster.
But I like thinking outside the box. There are many, many things taken for granted today that were considered impossible before someone started pushing the envelope.
"if you have a good car radio with decent sensitivity and selectivity - there, the useable range can be much greater."
This is probably what makes all the difference in the world to a Part 15 AM station, how it is received on the other end with what kind of receiver and what kind of antenna being used.
The print out (linked gif) will show us a pretty darn good baseline using less than optimum circumstances and equipment, which could be used for the baseline and called "common situation", or most normal type of radio receiver specs, most type of reception aerial utilized, and most type of environmental conditions..ie ground condition at TX point, and throw in type of grounding system used at the TX point.
However it is just one set of potential. I guarantee that read out will change if certain parameters of the input to the program were changed to reflect another area with different environmental conditions. I think however that the gif can be a fairly good starting point to what to expect out of a fairly decent setup in fairly good conditions, perhaps a little more.
RFB
This YouTube demo of the Potomac FIM 41 field intensity meter helps define the lower bound for "listenable" field strength on a good receiver (car radio). The signal drops to a noisy, but listenable level at about 60 uV/m. This seems to be more consistent with the range reports for Part 15 transmitters that are virtually always reported as a subjective measurement using a car radio.
Not to belabor the point, but to be consistent, we need to define what a 'good' radio is. Because some are much better than others, particularly in the AM section, which always seems to take a back seat to the FM section. I don't think that you can make the statement that a field strength of so much translates to a listenable signal - again, it all depends on the receiver.
If you take a look at the specs for a top end Marantz home stereo receiver, say, usually sensitivity for a mono FM signal is around 3-5 uv/m with some quieting. AM is generally 10 times that, at 25-35 uv/m. But they were made in the 60s and 70s when people actually listened to AM on a regular basis.
Car radios tend to have slightly better FM sensitivity than that Marantz, but the AM sensitivity sucks (how about that technical term?), if they actually specify it at all. If you attached an outside aerial to that Marantz receiver, you'd probably get better range with your Part 15 AM station than most car radios.
Radio8Z, in the very second submission to this thread, indicated that "wavelengths are proportionally shorter under water." He added, "Maybe we should put our antennas under water."
Hold action. Let's talk about that. How much water?
What if we built a ten-foot tall glass or plexiglass perfectly round water-tight "aquarium" with a 10-foot copper pipe right in the center of it, and fill it up with salt water.
Maybe we would get the equivalent of MORE than 10-feet in electrical wavelength?