Miscellaneous modeling stuff.

[The DB]

Here I am putting some modeling stuff that is unrelated to other threads. Bob85 a note, I will likely add your Starduster model request here.

To start I am going to show test model results for angled radials. This is on a Starduster type antenna, although these have four radials instead of three because it is easier.

The goal was to see if my new(er) method for AGT (Average Gain Test) adjustment, namely using a single segment feed point and adjusting its diameter, would be as effective at correcting this type of model as using the more traditional method of adding a few segments to remove said acute angles. It worked, their are only very minor differences between these models. The similarities go well beyond what this plot shows, every aspect of both antennas are extremely close, from variables used for things like antenna length, to SWR, to efficiency, ect. This tells me that with this antenna design traditional wisdom is but one way to overcome a known problem with this software.

This isn't the end all and be all of this test, however. I will also run a similar test at some point with upward angled radials, like on the vector antenna.

Assuming that works out as well, I will have no problem using my method instead of traditional wisdom when it comes to angles of less than 90 degrees.


The DB

 

[The DB]

A request by bob85 to show a starduster with a cap hat in comparison to a 5/8 wavelength antenna at the same tip height. I also threw in an AP at said tip height just because...

All three antennas are T6 aluminum, and all are tuned to resonance. As the I-10k would not adjust to a perfect AGT, I hadicaped the other antennas to match. All of these are slightly under reporting gain, and they are doing so equally.

The DB

 

[Needle Bender]

HUH! Looks like the 5/8 wins, though not by much, and only at higher angles.

 

[bob85]

Does anybody think this is why the astroplane seems better for talking to locals when we have europe using ssb on our legal FM band,
iceland have been in again several times recently, about 600miles,
worked them last time around on the 10k with no problem beating locals,
this time around its the opposite.,

 

[Marconi]

To start I am going to show test model results for angled radials. This is on a Starduster type antenna, although these have four radials instead of three because it is easier.

DB, what is the height to the feed point for the model at the beginning of this thread?

Are the slanted down radials attached directly to the base of the radiator or does your model include a small radial hub that provides some off-set for mounting these slanted radials?

I have a similar model over real Earth using 5 x 102" x 1/8" elements showing a much different pattern.

My patterns at various heights within reason shows the maximum gain lobe at a higher 30* degree angle or more...while still showing a modestly good gain at 11* degrees above the horizon.

The goal was to see if my new(er) method for AGT (Average Gain Test) adjustment, namely using a single segment feed point and adjusting its diameter, would be as effective at correcting this type of model as using the more traditional method of adding a few segments to remove said acute angles. It worked, their are only very minor differences between these models. The similarities go well beyond what this plot shows, every aspect of both antennas are extremely close, from variables used for things like antenna length, to SWR, to efficiency, ect. This tells me that with this antenna design traditional wisdom is but one way to overcome a known problem with this software.

Are you telling us that your new(er) method for controlling the AGT is what shows your antennas with maximum gains at lower angles and higher gain?

I'm thinking you're simply adding a short single segment wire between the base of the SD'r radiator and the radials and placing you feed point on the short wire. I think such an idea in modeling will get the feed point closer to the radial hub.

If not, can you describe for me your idea using a single segment feed point with more details or a picture of the feed point and antenna would be nice?

Also, how does you model over real Earth respond on raising or lower the model? Do you then, have to re-adjust this feed point wire diameter?

Edit: BTW what is the diameter for this short wire and one segment?

 

[Marconi]

Does anybody think this is why the astroplane seems better for talking to locals when we have europe using ssb on our legal FM band,
iceland have been in again several times recently, about 600miles,
worked them last time around on the 10k with no problem beating locals,
this time around its the opposite.,

Bob, I'm confused.

 

[bob85]

what i mean Eddie is when i had the 10k up at a similar tip height it worked better than my astroplane ( and my sigma ) for short skip like this side of europe and iceland,

i beat my locals talking to iceland on my 10k, bust the iceland pileup first call several times,

iceland has been in again recently and i can't talk over my locals on the astroplane but i seem to get less noise from europe when im talking to locals,

just my impression of what's going on with what i can hear and talk to on a hf set, nothing scientific just my impression.

i have had no long skip to get any impression of how the astroplane works over long distance,

it is as good or a little better than the 10k at 20-40miles and seems like i get less noise from europe using ssb on our fm band,

had no long skip to get any idea of how the astroplane works for that.

 

[The DB]

DB, what is the height to the feed point for the model at the beginning of this thread?

One wavelength

Are the slanted down radials attached directly to the base of the radiator or does your model include a small radial hub that provides some off-set for mounting these slanted radials?

Their are two models in that plot, one with a hub and one without. The model without the hub goes straight from the vertical element into the angled radials with no hub.

I have a similar model over real Earth using 5 x 102" x 1/8" elements showing a much different pattern.

My patterns at various heights within reason shows the maximum gain lobe at a higher 30* degree angle or more...while still showing a modestly good gain at 11* degrees above the horizon.

Both models have four radials, and they are 30 degrees off of vertical. Here is the layout for said model with no hub.

Are you telling us that your new(er) method for controlling the AGT is what shows your antennas with maximum gains at lower angles and higher gain?

Not at all. I was just looking to see if my current means of compensating for AGT would produce similar results to other methods of solving acute angle problems in NEC2 type software.

I'm thinking you're simply adding a short single segment wire between the base of the SD'r radiator and the radials and placing you feed point on the short wire. I think such an idea in modeling will get the feed point closer to the radial hub.

What you are saying about getting the feed point closer to the hub, this method can be used for that, however that was not my goal with those models. However, I took precautions to ensure that single segment wire was the same length as the other segments on the wire next to it.

What you are talking about is one way of minimizing said known problem, however, it was not what I was testing here.

If not, can you describe for me your idea using a single segment feed point with more details or a picture of the feed point and antenna would be nice?

In the current Astroplane discussion I mentioned that using a single segment wire I could adjust AGT by changing the thickness of said wire. Ghz24 told me about it. I was simply testing that idea with a model with a known problem to see if this method can compensate for said problem, I used a model with a hub as a comparison.

Also, how does you model over real Earth respond on raising or lower the model? Do you then, have to re-adjust this feed point wire diameter?

I haven't played with the models to much, just been to busy lately. Other models required me to change the single segment wire to maintain a reasonable AGT when changing the antenna's height do require some adjustment to maintain the same AGT, so offhand I predict that the answer to your question will be yes.

Edit: BTW what is the diameter for this short wire and one segment?

The rest of the antennas wires have a radius of 0.25 of an inch. That wire is 0.1125 of an inch. The length of the vertical element and four radials are 100.104 inches, this includes the separate segment on the vertical element. That single segment element is calculated by the software, and to get that length you take the 100.104 number and divide it by 25. The antenna feed point is 379.896 inches off the ground. This is the model with no hub for the radials.


The DB

 

[The DB]

I was playing with a dipole that has a petlowany coil on both sides. This was spurred by a post in the ham radio antennas section of this forum referring to a Tak-tenna brand antenna. I am very surprised at the results of this model.

Here is the plot.

All of these antennas were mounted vertically above the same ground, and their feed points were all at the exact same height, and these antennas are all either center fed or center fed like antennas. For the modelers, all of these antennas have the same AGT, and that is 1. One of these antennas is handicapped compared to the others, and that is the Astroplane, whose model is made out of aluminum (the others are all a perfect conductor). All antennas are tuned to or very close to resonance.

The petlowany coil antenna did the worst, but still, a 17 inch long antenna performing close to an antenna that is that is a little over 17 feet long (the dipole reference)? That is surprising to me. I guess I found my next antenna design to study...

Here is the layout of the petlowany coil antenna model I tested.

The DB

 

[bob85]

I can't get my head around that one DB, 17" vs 17ft, got me scratching my head

 

[HomerBB]

I can't get my head around that one DB, 17" vs 17ft, got me scratching my head

It's got to be that new modeling trick he learned where you make a sigment fatter and fatter and longer and longer by bits until the antenna is as powerful and magni-genius as the other beams and things you are overlaying...

 

[The DB]

Two notes on the antenna model with the petlowany coils shown above. Homerbb mentioned in another thread...

I tried to make one 3-4 yrs ago. Never tuned up

In that model, R near resonance is 1.27. I am pondering how to tune such an antenna design, I will have to play with different spacing between the individual loops to see how much of a difference that makes. With the pictures I am seeing of antennas that have already been made, that one inch separation may be to large for this antenna on the CB band the model was made for, but that will require building a more adjustable model to test properly.

The other thing to note is the current distribution on this antenna.

Two things to note here, the current peak isn't at this antenna's feed point, and even more surprisingly, the two that exist on this antenna are not even in the exact same place relative to the feed point. As the antenna's sides are mirrors of each other, the only thing that can be affecting the antenna this way in the model is the earth below, however, the lower coil is near 32.5 feet, while the upper coil is closer to 35.5 feet above said earth. I don't see the earth being that far below, on its own, making that much of a difference, so at this point I am proposing that the loading of the different coils are amplifying the effects of said earth.

I need to make a model that I can modify various things on easily, such as the spacing on the coils. Perhaps then I will learn more.


The DB

 

[rabbiporkchop]

It would be interesting to try that antenna mounted slightly above the roof on the rear of a Freightliner Cascadia

 

[Riverman]

Marconi and DB,

Anyway to model one of these?

http://www.parelectronics.com/omnis.php

Am mostly interested in the OA-50. http://www.parelectronics.com/oa50-specs.php

 

[The DB]

Two additional things to note, the antennas from http://tak-tenna.com/ and many of these that have been made are closer to the earth, which will, in and of itself, raise R, although not likely enough to tune on its own. Further, looking at their web site closely, those are tapped coils. Here is the image on their main site being used as an example.

If those are tapped coils, that might solve all tuning problems, all I need to do is use tapped coils in the models myself... These coils are also much larger than the ones I used in the models... With such a system I can see the potential for the antenna to be tunable over a fairly wide range of frequencies, or perhaps length of the antenna inside of said coils?


The DB