What W8JI says about a 1/4 wave vs. 5/8 wave

[GnG8d]

If you put the antenna over real ground at Z 0 doesn't this place the antenna directly on top of the ground?.

Yes.

This would remove the multiple lobes and nulls created by ground reflections but it doesn't seem to reveal the slightest downward radiation below 0 degrees.

I'm not real sure what I was trying to say. But even though lobes below 0* are not shown, it does seem to try and calculate them.

 

[Marconi]

I'm not real sure about the patterns that Eznec makes, but I think their patterns over real Earth are taken from the perspective while standing on the ground at any point beside the antenna and out to the horizon or maybe even out to infinity.

So, with elevation set at any height above the Earth you will see RF below the antenna down to the Earth. I think the 90* degree line represents the Earth's surface.

 

[GnG8d]

You should be able to use your arrow keys and rotate that pattern all around like a ball and see it from any angle. But it never shows radiation below horizontal for some reason. Like it does in free space anyway.

 

[Marconi]

You should be able to use your arrow keys and rotate that pattern all around like a ball and see it from any angle. But it never shows radiation below horizontal for some reason. Like it does in free space anyway.

I agree 359.

BTW, have you seen the movie "Atlas Shrugged," by Ayn Rand yet? I had a bad time in college reading the book, I could not believe the issues she raised about America. The movie is a must see, if you would like a look from the past into our future, so-to-speak.

 

[Marconi]

Thanks for the interesting reading you linked, Marconi.

Just sandbagging and seeing what happens.

BTW, the first 5/8 I ever posted about building was a good antenna compared to the A99 it replaced. It has four drooping radials instead of flattened out like the most of them are. I was under the impression in that configuration it would help with matching. . . In a different location than it was up originally it seemed to not do as well. When I switched to the horizontal elements I noticed no improvement over the slanted version.

What do I think?

Only one thing, actually, without further thought - location. After reading some of the info on the links you provided perhaps I'll pay more attention to coax lengths, reconsider GP formation, and more analysis of height. It seems the one thing that no one can accurately model, or plan for, is earth type or conditions.

BTW, the 12 x 3' long GP set up on the latest 5/8 has been a dismal disappointment. I have a 102" whip above my 4el Yagi now which seems to do as good as, if not better, than the 5/8. I will be removing the radials from the 5/8 and remounting it directly above the Yagi to see if that improves its response on rx and tx.

Okay, back to sandbagging. None of this is based on knowledgeable scientific data.

Homer, you tell us you changed the location and the antenna didn't seem to work as well as before. You also mention accuracy in modeling depending on the Earth type and or conditions. Well, conditions certainly play a heavy part in comparing antennas, and that is why I do A-B side-by-side comparisons, albeit I might get even that wrong.

Eznec5 modeling software does however, allow one to change the conditions for soil, and I think it is based on the PBA pseudo-Brewster angle ideas that are noted in the ARRL 17th edition 3-3, or some variations on that idea. There the soil is categorized into a range from "Very Good" to "Extremely Poor" with "Average" in the middle. Eznec5 defaults to average, but it can be changed. This affect on antenna performance and angle is dramatic and that is why we casually claim all the time...location, location, location.

If you first made comparisons over Earth where the soil conditions were average, and then moved to conditions that where very poor or extremely poor, what results in performance (gain and angle maxima) would you except to see with another set of comparisons for the same antenna? I know that I was surprised at such results, even though I know there are such examples tested and published on the Internet.

I'll make a model to demonstrate this affect if you can give me a wild guess, or maybe you already know...anybody.

 

[HomerBB]

I think I need to clarify. Although the modeling software has a range of options for soil types, we often can only guess what our soil is like. After 2 to 3 weeks of solid rain my soil is different than before at least temporarily, I'd think.

The example of the 5/8 with drooping ears versus one with straight was meant as only an example of differences in construction that seemed to change little to none. Also, I used the drooping ears antenna in a different spot to represent seeming degradation in performance by a move of the antenna a mere 30 feet over what should have been near, if not identical mounting parameters. The only way I might have known the two spots were different would have been by some soil testing process. My point is that I would have modeled both spots the same, yet performance would have shown they were somehow different.

 

[GnG8d]

BTW, have you seen the movie "Atlas Shrugged," by Ayn Rand yet? I had a bad time in college reading the book, I could not believe the issues she raised about America. The movie is a must see, if you would like a look from the past into our future, so-to-speak.

I've read some about her, but I'd be better off with the movie. I have two books here I want to read now and my wife brought another one home a couple weeks ago ......... that's a winter time project :laugh:

 

[Marconi]

I think I need to clarify. Although the modeling software has a range of options for soil types, we often can only guess what our soil is like. After 2 to 3 weeks of solid rain my soil is different than before at least temporarily, I'd think.

The example of the 5/8 with drooping ears versus one with straight was meant as only an example of differences in construction that seemed to change little to none. Also, I used the drooping ears antenna in a different spot to represent seeming degradation in performance by a move of the antenna a mere 30 feet over what should have been near, if not identical mounting parameters. The only way I might have known the two spots were different would have been by some soil testing process. My point is that I would have modeled both spots the same, yet performance would have shown they were somehow different.

Maybe this will give you and idea of the soil conditions in your area. That said though, it only provides a general idea.

 

[Marconi]

Homer, here is a version of the ARRL chart on conductivity and dielectric constants for common types of Earth in the US. This chart gives some descriptions for the various data that we can all recognize that might help identify the conditions in different areas.

View attachment ARRL ground affects.pdf

 

[HomerBB]

Thanks, Marconi

Looks like I am between poor and very poor with an 8.

 

[GnG8d]

Thanks, Marconi

Looks like I am between poor and very poor with an 8.

no no, that 8 is .008 S/m

 

[Marconi]

no no, that 8 is .008 S/m

You're right 359, but the 8 = millisemens/meter and that is noted on the chart, so both numbers are correct.

BTW, Eznec's default value is Average soil condition = 13/.005.

 

[GnG8d]

You're right 359, but the 8 = millisemens/meter and that is noted on the chart, so both numbers are correct.

BTW, Eznec's default value is Average soil condition = 13/.005.

No, he was looking at the 8 as the dialectic constant I believe.

 

[HomerBB]

I looked at the map, and NW Arkansas is an 8. Then I looked at the chart and just assumed the 8 meant the dielectric constant, which fell between 5 and 10. I didn't read any instructions for the two.

So which is what?

 

[GnG8d]

I looked at the map, and NW Arkansas is an 8. Then I looked at the chart and just assumed the 8 meant the dielectric constant, which fell between 5 and 10. I didn't read any instructions for the two.

So which is what?

The 8 on the map represents .008 S/m or 8 mS/m, the dialectric constant of around 12-14 which is good/very good.