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Davemade groundplane / birdcage antenna

I see the red errors, and the segment counts. I am assuming these you point out to Express concern that the modeling may be manipulating the results by changing up small but crucial details within the models. I am lost on the High Accuracy thing.
And, yes, I had a lot of difficulty trying to tune my homebrew antenna until I added standoffs to the bottom of the cone.
 
HomerBB said:
I am lost on the High Accuracy thing.
And, yes,
Click to expand...

I just trudged through and read the manual on High Accuracy, and It is a feature that is used with the highest end Eznec that is able to use the licensed versions of NEC4. The feature is not functional using NEC2 and all the other lesser versions even several options above my version.

The High Accuracy feature is only used when a horizontal wire at or below the ground is used up to about 6" inches deep. The results of using this feature with NEC2 Eznec are unpredictable patterns and errant resistance values. Do you see the High Accuracy feature being used on the Vortex models?

HomerBB said:
I had a lot of difficulty trying to tune my homebrew antenna until I added standoffs to the bottom of the cone.
Click to expand...

Thanks for confirming my old fuzzy memory.
 
HomerBB said:
I don't see the HA on the Vortex model. I just look at what you point out.
Click to expand...

Well the images I sent thru didn't come out nice, clear, and bright. Look at the Control Center image on the Vortex Mark I model I sent with the image of the antenna base and the red coax choke. Check the list of functions in the white screen area and you should see Ground Type (Real/High Accuracy.) This means the HA function is on and active.

I sent the landscape images along just so we can see more of the 2 Control Center images that Vortex published on their Website.

I fixed my Vortex Mark II model to a point where the Antenna View, pattern, maximum TO angle @ 8* degrees, with 5.35 dbi maximum gain, all are very similar to the Vortex Mark II model as published.

All I did was to set the overall radiator length to a 3/4 wavelength instead of 1 full wavelength.

Homer, this only makes my model look similar to what we can see as published except for the bad match. Vortex only shows us the analyzer images for the match...not matching results from the model.

I might be able to get the match fixed by using one of the Eznec matching tools, but because Vortex shows no tools used...I decided to try and do the same. So, if I was able to fix the bad match adjusting this 3/4 wavelength, and I could get the gain to show the correct value...we would likely see the reported gain minus the reported error in gain or:

5.35 dbi - 1.20 = 4.15 dbi as a result of fixing the overstated gain error.

Model:
1. is the Free Space Control Center page to show the Average Gain results that shows the model is overstated by 1.20 db and needs to be subtracted from the reported gain 5.35 -1.20 = 4.15 dbi

2. is the Real Earth Control Center page showing no tuning tools were used and the Ground Type for my model is set at (Real/MININEC).

3. is the Antenna View that looks similar to the Vortex model and shows the radiator length of r-329.4" inches in the title. I made an error in the length and it should be 325.387" inches.

4. shows the antenna pattern which is similar to the Vortex model and shows us the gain, which is overstated, and the maximum TO angle.

5. shows the matching results for this model and it needs to be tuned better.
 

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So you are getting a 2.6 SWR without adding a matched? Says no transformer, no network...

Soon be time to share all dimensions for home brewers.
 
what was the reported gain for the vector 4000 at the same height Eddie,

4.15dbi is what sirio claim for their cx vhf & uhf 3/4wave coaxial j-poles and both versions of vector 4000.
 
HomerBB said:
So you are getting a 2.6 SWR without adding a matched? Says no transformer, no network...

Soon be time to share all dimensions for home brewers.
Click to expand...

Homer, I have a feeling that this antenna can possibly be made a full wavelength long, but it will require something more to get it to match, and we see little to nothing about this antenna and matching so far.

Check the Vortex Q82 Mark II model on my post #26. That model is a full wave length model and is what I started with...per Bob's dimensions and telling me he has heard it is 1 full wavelength.

In my post #26, I posted 2 images from the antenna model that already shows the basic dimensions. See more details below.

Later today I took 108" inches off the top of the radiator for that model and the match improved a lot, but it was still not very good. I checked the math and the antenna was close to a 3/4 wavelength overall. I fiddled with the length in small increments and it is still close to the same, no-way-no. Since this is a 3/4 wave antenna and is end-fed...I would expect it to show closer to a good match, but it doesn't as yet and the antenna is still inductive. I think this induction is from the much longer radials.

The radiator is 0.80" x 329.4" in overall length.
The radials are 0.75" x 161.752"
The off-set brackets are 2.50" inches long at the base
The feed point is direct fed at the base of the radiator.

We're not there yet, but thanks for your comments.
 
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bob85 said:
what was the reported gain for the vector 4000 at the same height Eddie,

4.15dbi is what sirio claim for their cx vhf & uhf 3/4wave coaxial j-poles and both versions of vector 4000.
Click to expand...

Sirio reports 4.15 dbi gain for their NV4K and my best V4K model with a simulated gamma match feed point shows 4.32 dbi @ 8* degrees and it is a 3/4 wavelength.

Bob, I went deep into the Vortex Wevsite today looking for details, and the only thing I found besides these Vortex guys seem to be flush in money, travel all over the world doing radio DX'ing, among other things that cost a lot of money, like charter yachts, big hotels or grand lodging, and charter flying, was I also saw a big CTE banner on a wall in a picture of Steve and Walt. They seem to be the principles of Vortex. Images are in the Home section near the bottom.

I was looking for some words or a suggestion that the Mark II was a full wavelength antenna.

I haven't finished with this model, but what do you think I should now try 1st.

Get this shorter model to match better and likely see the gain drop, or set the antenna back to the 1 wavelength and try and fix that using my tuning tools and see if the thing will perk up and show a big low angle gain at 36' feet.
 
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Bob, thanks for clearing that up. I think my Mark II model is close. I have not considered the Mark 1.

I still have some issues about the models, mine included, but I like the construction ideas these guys present. I've also just seen that Vortex does a lot more than the Q82 line.
My Bird Cage model with a big ? mark is still on the drawing board. I think I see a larger than typical radial base mount bracket, with 8 radials, and 4 supporting loops. I think I also described it earlier as a 5/8 wave with a 3/8 wave cone, and I was not sure about the matcher, but you described it as a capacitorless gamma match. Is this about right?

I see in your link, where 163x549 Lee says the Bird Cage is a full wave antenna, but when I clicked on the More Information button...I got a request to sign on to Pinerest. If you find anything where Lee is talking about the Bird Cage...I would be interested.
 
I wonder what a 2m version that is 63" overall from the bottom of the cone and sporting a 31.5" cone look like..?
How are you determining the top cone ring diameter?
I am thinking the top of this 2m experimental unit would be 10", or 31.5" circumference...

Do you think I could wrap one of these in aluminum tape for a radial cone? :sneaky:

Screenshot_20200328-110645_Google-01.jpeg
 
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HomerBB said:
I wonder what a 2m version that is 63" overall from the bottom of the cone and sporting a 31.5" cone look like..?
Click to expand...

Homer, it may be a little early since the match is still off. But you could give me your 2 Meter frequency and I could scale my Mark II model...and give you the dimensions used.

HomerBB said:
How are you determining the top cone ring diameter?

I am thinking the top of this 2m experimental unit would be 10", or 31.5" circumference...
Click to expand...

I figured I would still be at 27.205 MHz, so I kept the loop diameter the same as my S4/NV4K at 30" inches. I use an Eznec Tool to make loops, but getting all the data parameters right can be a challenge. See this Tool in PDF file below. Ignore the data...that is for the last loop I made, and that is too bad.

If I scale this model to 2 M then I'll post the dimensions in the Eznec model so you can check and compare the numbers.

HomerBB said:
Do you think I could wrap one of these in aluminum tape for a radial cone? :sneaky:
Click to expand...

I think you once did an A/P model this way and you reported it worked well.
 

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