ground to model over

[ghz24]

Freespace is a great equalizer but, at cb frequencies it is virtually impossible to escape the effects of the ground
I'd like to find or reach a consensus on what type kind of environment and ground we should model over so as to adequately demonstrate the properties (in general) for the antenna being modeled .
Besides freespace and perfect ground 4nec2 offers 3 environments each with a plethora of grounds to chose from , pastoral hills, mountainous , fertile ground ,rocky steep hills, marsh ..... none of which will really accurately represent your 20 (except seawater maybe) If you want to play with those great ,it may answer why certain antennas don't perform as expected for all people/location.
They don't make for level playing field to compare models over though.
The first four ground types are more general and at least make candidates
The three environments are: fast ,real and mini-nec .
Each has the choice of amongst others: good, average, moderate,and poor
I've uploaded a series of plots that demonstrate the effect of these environments and qualities
have on 3 antennas : A moxon for pure horizontal polarization. a sigma4 for vertical
and a directional Circular polarized antenna.

Marconi do you have other environments to chose from or only mini-nec?

Which one of these do you think we should use.
Which one doesn't give an undue advantage to one type or another?
Considering how close the patterns are does it even matter as long as we stick to the same one?
Are any unsuitable?

 

[The DB]

In the past I have primarily used real/average ground for the models I have posted unless I have stated otherwise. More recently, since the last models I have posted here or anywhere, I have played with various different ground types and, just as you have above, noted some differences. Which one is more accurate would depend on the ground conditions where you are transmitting/receiving from, and honestly, most people really don't have the ability to measure such things themselves...

Her is another example to add to yours of a 0.66 wavelength vertical over four 0.25 wavelength radials. Yes, this antenna was intentionally modeled to be longer than the mythical 0.64 magic maximum electrical wavelength... A note, the grounds used here are real/good, real/average, and real/poor.

Something to notice when it comes to the lobes of these three identical models aside from the grounds they are over, average ground has the lowest gain, and strangely, average ground is the only model here that has a higher angle lobe that is more dominant that the lowest angle lobe... I guess there goes the 0.64 wavelength antenna being the absolute best low angle gains in all circumstances as the model shows it is possible to exceed that length in some cases depending on the environment the antenna is in. I think it is worth noting that for some ground conditions that you could make the antenna even longer than this while still having a dominant low angle lobe, but that is another discussion...

It is also worth noting that the good ground model above has two lobes, while the average and poor ground models of the same antenna the same height above ground have three.

Anyway, what I would recommend is a de facto standard that we modelers can use for said ground for posted models, I would recommend the real/average set as that is what I tend to use unless stated otherwise. Or we can opt to just note it every time we post a model. I'm pretty sure Marconi also uses average ground of some type for the most part as well with his EZnec models.

I do have to agree that using average ground does not necessarily produce models with an average pattern compared to all of the other possibilities, but I don't think that was the point. I was going to say here that average ground has an approximate average of conductivity and dielectric constant for ground, but that is only half right. Only the conductivity is near average, the dielectric constant variable used is more than twice as large as the good and poor ground types... I wonder why that is.

I, personally, have no problem with using whatever standard or method we settle on. Otherwise I will simply note the ground used for whatever model I happen to make in the post with the model...


The DB

 

[M0GVZ]

If you're in the USA there is actually a database for the entire USA which states the ground conductivity for where you are. I can't recall where I saw it but there's one out there. Popping that in will give the most accurate results.

 

[The DB]

https://www.fcc.gov/encyclopedia/m3...d-states-wall-sized-map-am-broadcast-stations

Unfortunately I think this is really only accurate at AM broadcast frequencies which is where the measurements were taken. The electrical conditions of earth do change at different frequencies...


The DB

 

[ghz24]

I originally picked average figuring it was just that, average.
due to my recent comparisons it became obvious that average
is far from average.
"Average" values consistently fall outside the range defined by good and poor
How can average be at one extreme not in the center ?
I think we must discard average as flawed in definition at least.
I reluctantly (most my models are already over average) suggest moderate.

 

[The DB]

I originally picked average figuring it was just that, average.
due to my recent comparisons it became obvious that average
is far from average.
"Average" values consistently fall outside the range defined by good and poor
How can average be at one extreme not in the center ?
I think we must discard average as flawed in definition at least.
I reluctantly (most my models are already over average) suggest moderate.

At the moment I am in agreement with this. As far as ground conditions go, moderate seems to be much closer to an "average" than "average ground".

I have been toying with the idea of modeling a few test antennas over the rang of given ground types, manually controlled, and seeing how various aspects affect the output, and using that data to make my own version of "average ground" that is closer to an average...


The DB