considering an M400 starduster. whats the deal?

[Staybolt]

Wow i cant believe the debating back and forth over a 1/4 wave antenna.

 

[The DB]

Not all of this is about the Starduster, their are discussions that alludes to other antennas as well, such as a about a page or more of posts referring to the Astroplane, and some discussion on 5/8 wavelength antennas and the radials that go with them, and more. Just because their are a few pages in a single thread on this forum does not necessarily mean that all of those pages can easily be described by the title of the thread.

And their are a lot of people that believe as you do about the Starduster. That being said, the fact that the radials are angled down can easy be used to formulate a very good argument against that idea. If you like I'm happy to play devils advocate for you...

In my view, however, it doesn't really matter. Put it at the same tip height as pretty much any other CB antenna, and if you notice a difference between the two it is because one of them has a problem.


The DB

 

[tba02]

Just because their are a few pages in a single thread on this forum does not necessarily mean that all of those pages can easily be described by the title of the thread.

That is probably as accurate or more accurate than many posts in this thread.

 

[Staybolt]

I have an astroplane and a sigma 4 both are some of the most highly debated antennas ever made.. All i know is they work......

 

[Marconi]

And their are a lot of people that believe as you do about the Starduster. That being said, the fact that the radials are angled down can easy be used to formulate a very good argument against that idea. If you like I'm happy to play devils advocate for you...

In my view, however, it doesn't really matter. Put it at the same tip height as pretty much any other CB antenna, and if you notice a difference between the two it is because one of them has a problem.

DB, I'm one many that really has a high regard for the Starduster design...just as it is.

If you want to play devil's advocate, then I would like to hear your idea...in spite of the fact you also say, "...it doesn't really matter."

 

[wavrider]

I second Marconi I also hold the starduster in high regards as a direct fed 1/4 wl vertical that works as well as any GP I have ever put in the air

 

[The DB]

f you want to play devil's advocate, then I would like to hear your idea...in spite of the fact you also say, "...it doesn't really matter."

Sure, why not...




The DB

 

[Mark Scannura]

So is this modeling telling us that with earth ground a standard 1/4 wave GP with same GP radials at 0 degrees should outperform the SD with all things being equal?

 

[Marconi]

DB, very good video as usual. Thanks

I see the title for the models changing in you video from the horizontal up to 80* degrees, as noted at the top of the 4Nec2 control page. However, I don't see the impedance or the SWR change any if at all as you slant the radials down.

The whole idea for slanting the radials down on a 1/4 wave GP is to raise the impedance and thus make the SWR improve.

My model overlays below are not tuned and tuned showing AGT = 1 for each iteration in angle.

I also set my horizontal model to show similar impedance close to what you did Steve, with R = 26.69 ohms and X= +2.657 ohms = 1.875 SWR just to get started using a similar base line.

My models have 3 radials at 107" inches and varying lengths to resonance for the radiator. I also added a mast 77.5" x 1" inches below the hub for these models so I would hopefully be close when I set my models over Real Earth. I have a reason for setting this mast to these specific dimensions.

My models show close to similar gain results to your models and I think your conclusion is pretty close when the radials start to get below 45*-50* degrees.

I have not run these models over real Earth yet.

 

[Marconi]

Here are my SD'r models at 80, 60, 40, degrees slanted down and the baseline model with horizontal radials over Real Earth. My models look to show an improved gain as I drop the angle down including 20*,40*, 60* degrees. The model with horizontal radials is by far the worst model with a very high maximum gain angle. Also, the model slanted down at 80* degrees and close to the radiator...looking like a 1/2 wave dipole is not the maximum gain setup one might expect.

The best model here is the 40* degree angle and then the 60* degree angle, both with almost identical gain at a maximum angle of 11* above the horizon. I forgot to do 20* degrees.

I let Eznec decide what angle is maximum for each model as usual, but you have to pay close attention to the angle for each model, and not just take the gain value indicated as what is best.

I can't account for the skewing in the pattern we see with the 40* degree model in "Black." I did use a model with a simulated physical hub that pretty much is to dimensions and it is a large object, considering it is near the feed point. I could argue this hub might make some difference in a model.

I will have to check this hub out more closely for some possible error in my design.

 

[The DB]

So is this modeling telling us that with earth ground a standard 1/4 wave GP with same GP radials at 0 degrees should outperform the SD with all things being equal?

At the height modeled, and over what the software calls moderate ground, yes.

I see the title for the models changing in you video from the horizontal up to 80* degrees, as noted at the top of the 4Nec2 control page. However, I don't see the impedance or the SWR change any if at all as you slant the radials down.

SWR does change as I angle the radials down. You will note that to show the geometry for the model I added I had to click on the geometry window after adding said model. I didn't click the main data window to show the changing SWR as that wasn't what I was trying to show, but SWR does indeed change with the angle of the radials.

With the red and black models in the post immediately above this one, one or both seem to be skewed as one shows a higher gain in one direction, and the other shows a higher gain in the other. That is an odd thing on what should be symmetrical antennas. Its not like we are adding matching systems or anything that would cause said skewing...


The DB

 

[Marconi]

SWR does change as I angle the radials down. You will note that to show the geometry for the model I added I had to click on the geometry window after adding said model.

Well, Steve, that step confused me and went right over my head. Sometimes, I barely get a clue what you do when clicking on the buttons and switches in 4Nec2. If I did a video, I might come across the same way. I did see the title name for the model changing at the top of the control screen image, but I was looking for the details to change as well.

I didn't click the main data window to show the changing SWR as that wasn't what I was trying to show, but SWR does indeed change with the angle of the radials.

Well, sometimes I can see a little bit of the details for what you're doing on my end of your videos. I assumed all the data shown would have been updated, just like the title for the next model in the iterations I saw was updated..as you changed the angles for the radials down.

Note: I also noticed that at some point in your video the details for this main screenshot are very clear and easy to determine. However, at other points in the video, this same screen is blurred and I can't read any detail at all. My eyes are not the best so it could be me.

With the red and black models in the post immediately above this one, one or both seem to be skewed as one shows a higher gain in one direction, and the other shows a higher gain in the other. That is an odd thing on what should be symmetrical antennas. Its not like we are adding matching systems or anything that would cause said skewing...

I agree, I was surprised too. That is why I mentioned it and made a specific comment in my post. I figured anybody looking at the post...might be confused by what they saw.

Steve, I removed the large hub I had for this SD'r model and made the radial offset to the radiator = 1.5" inches. I used a single 1 segment short wire for each radial instead of the large hub. That made no difference, the asymmetry is still there.

 

[The DB]

Well, Steve, that step confused me and went right over my head. Sometimes, I barely get a clue what you do when clicking on the buttons and switches in 4Nec2. If I did a video, I might come across the same way. I did see the title name for the model changing at the top of the control screen image, but I was looking for the details to change as well.

Well, sometimes I can see a little bit of the details for what you're doing on my end of your videos. I assumed all the data shown would have been updated, just like the title for the next model in the iterations I saw was updated..as you changed the angles for the radials down.

Note: I also noticed that at some point in your video the details for this main screenshot are very clear and easy to determine. However, at other points in the video, this same screen is blurred and I can't read any detail at all. My eyes are not the best so it could be me.

When it comes to the not automatically updating the info on the screen, it may be another thing from running the program in linux instead of its native windows environment.


The DB

 

[bob85]

Do you get the same reduction in gain change when the mast is choked just below the radial tips about 1/4wave from feed-point ?

 

[Marconi]

Do you get the same reduction in gain change when the mast is choked just below the radial tips about 1/4wave from feed-point ?

Bob, I'm not sure this goes to your point. These models show there is a small difference when the choke is placed at the feed point vs. at the bottom of the radials.