Davemade groundplane / birdcage antenna

[Shockwave]

Yes Eddie that's what im getting at, 1/4wave cone & 3/4wave monopole puts the hoop close 1/2wave from the tip where current is lowest & voltage is highest,

pictures can be misleading as we have seen in the past,
the cone looks to be more than 1/2 the length of the radiator above it, could it be a full wave radiator with 3/8wave cone,

VORTEX use a 3/8wave cone.

Lengthening the cone delays the phase feeding the top section and introduces beam tilt. It is likely that the builder of the Vortex noticed the typical mounting heights used on 11 meters showed improved gain on the horizon with a longer cone. As the height or frequency increases, the optimum cone length does become electrically shorter than 3/8 wave but more than 1/4 wave once you add the loop on top.

 

[bob85]

The matching looks like a capacitorless gamma tapped part way up the cone,
if it is, sirio use the same style gamma in their cx series coaxial j-poles tapped up the monopole,

longer than 1/4wave is ok on vhf/uhf, its not so practical for 27mhz with our weather,

3/8wave would be as far as id be willing to go and expect it all to hold up in high wind.

 

[AudioShockwav]

Eddie,
CCM or Concrete Man, he has been a member here under several names.
He posted a picture of this very antenna on the floor of his shop years ago in th building stage.
I have searched but can't find it anymore.

73
Jeff

 

[G GOLLY WAlly]

I don't really have anything to add to this except I'd take one, and the first thing I thought when I saw it was, that looks more like an upside down tomato gage than a bird gage. But that's just me

 

[Marconi]

Bob, I think I've heard you talk a little about your ideas for the Vortex brand here and there. I also think, for long standing reasons, why you might be persuaded to look into these claims and ideas some more.

Recently, I see you getting curious again and wanting to do a project looking for some proof. This is about the same as I try to do with my models when I can see a little of what might be going on with the construction. Maybe Homer BB has some interest here, maybe for a higher frequency and I can scale a model to CB.

Maybe when you finish doing your project you can give me some dimensions and matching details and I'll try and make a model.

Good luck and keep me posted.

 

[HomerBB]

It is interesting. However, I see no clear dimensions posted, only speculation.
If I were to make one, I suppose it would be a bigger basket on a V4k vertical.
The matching system seems foggy, too... Coax center tapped to the basket, no capacitor?

 

[bob85]

Eddie,
i have all the tube i need to make the 1/4wave cone version, i could go longer with the same tube if needs be but id be sacrificing wind survival unless i put extra spreaders on there,
no point in building a 100mph antenna & putting a 70mph cone on it,

i would like to see a model of the mk2 VORTEX done by somebody other than VORTEX that includes the mast/coax and average ground.

 

[Marconi]

its claiming full wave but that could be 3/4wave monopole + 1/4wave radial sleeve,
looking at proportions if it is a full wave monopole the sleeve would have to be much longer than 1/4wave,

Bob, I will keep your full wave idea in mind. At 27 MHz I get 3/8 WL is about 162"+ inches for the radials.

Eddie,
CCM or Concrete Man, he has been a member here under several names.
He posted a picture of this very antenna on the floor of his shop years ago in th building stage.
I have searched but can't find it anymore.

73
Jeff

Thanks Jeff, but it still doesn't spark my recollections.

If I were to make one, I suppose it would be a bigger basket on a V4k vertical.

The matching system seems foggy, too... Coax center tapped to the basket, no capacitor?

Charles, that is basically what I would do with a new model for this Bird Cage (BC) antenna, It would be easy to change the radial length but tedious to added all the braces. It would be fairly easy to just change the radiator length. Exnec makes that easy and has a tool to do it.

That said the match could be a problem, even if I could use a capacitorless gamma, as Bob called it.

You comment that the coax center is tapped to the basket. I see a short green wire mounted in the top of a connector screwed into the base radial bracket. The wire looks to be to be a direct connection to the base of the radiator. That is where I set my feed point for my model of the BC. I stopped here and changed over to working on the Vortex Q82 after Bob gave me some dimensions.

Nothing but questions right now, but more to come.

 

[bob85]

I have not seen the matching up close Eddie, im going by what i think i can see in the images,
a gamma does not always need a capacitor, you can adjust the antenna to compensate for the reactance the gamma introduces,

sirio cx coaxial j-poles have a brass tube from the so239 tapped up the monopole inside the lower 1/4wave sleeve.

 

[Marconi]

Bob and Homer, I'm sorry the image are not very good.

I have question about the red wire coil that is obviously in the picture below for some version of the Vortex antenna that is not identified.

So, what is the coil for and which antenna do you think we are seeing here?

 

[Marconi]

Here is the model I identified as the Q82 Mark II. I made a FS model first and the Average Gain for the match shows good, but not perfect.

I set this model up with nothing done except to set the radials to 161.752" inches and to make the radiator length to a full wavelength. So we have 3/8 for the cone and 5/8 for the radiator above the cone = 8/8. I know, nobody is saying this is correct, this is just a start based on Bob's idea about the 1 wavelength claim somewhere for one of these 3 antennas in our discussions.

I'm still calling it eye-candy.

Model is (Q82 Mark 2 wMnISOnC nM2 36')
wM = with mast
nISO = no isolation
nC = no choke effect
nM2 = no matching was attempted here and this was my 2nd model done so far.

1. The image of the Control Center, was added to show the Real Ground Type I used (Real/MINIINEC). The Vortex site shows they used for their model (High Accuracy). When I set my model to High Accuracy it gives me a one time warning. It says One or more wires connected to the real, non-MININEC ground. And they add, this will cause a resistance at the connecting point which you may not expect. To me, this means the mast connected to the ground.
2. I added two antenna views to show the lengths for the radiator, the radials, and the red (o) the Feed Point.
3. Is the pattern, but it is basically meaningless at this point but it does give the idea for this design to compress the higher angle lobes.
4. I added the Antennna Wire Descriptions for my own reference.
5. Is the Source Data which shows the matching results...which I was concerned that might happen with such a design. IMO, this antenna requires a transformer, so maybe this is why we see a coil in the picture I posted above. That said though, I could be wrong and that coil could be a choke in line with the analyzer.

Because I'm a little confused trying to think about all 3 of these antennas, I stopped both the Bird Cage and this Vortex here.

 

[bob85]

The pic with the red choke is on the mk2 photos Eddie,
radials look more like 3/4" than 5/8" so id say it is the mk2,

can't be sure but it looks like they have a choke on the patch lead from analyser to antenna.

 

[HomerBB]

I do see the toroid core choke. I also think it is on the analyzer patch cord. I have done that to try to see if there is a difference in readings with and without it when I suspected influencing common mode currents.
Marconi,it is definitely not a transformer. It's a choke.

 

[HomerBB]

Although the pattern looks better on the second model, and the maximum radiation is one degree lower, I prefer the first one for it's greater gain, and the longer basket to vertical length ratio. It contains the out of phase currents better. If not for the deep null at useful elevations it would look finger lickin' good.

 

[Marconi]

Marconi,it is definitely not a transformer. It's a choke.

Homer I agree that looks like a choke

Although the pattern looks better on the second model, and the maximum radiation is one degree lower, I prefer the first one for it's greater gain, and the longer basket to vertical length ratio. It contains the out of phase currents better. If not for the deep null at useful elevations it would look finger lickin' good.

Here are some things to check out with these two Vortex Eznec models that are not very convincing for me.

I've already posted about Vortex using Real/High Accuracy for the Ground Type in my post #26. I don't understand this function technically, but it does have some special use in modeling related to the ground. Eznec doesn't produce an error message for no reason. I never use this function, so I don't see the message, but it does not stop the model from working so it is not a critical error, it is a warning and I try to stay away from warnings.

The Mark i shows 1 wire number for the radiator, 4 wires numbers for the radials, and the rest of the 39 wires are for the radial loop. No mast wires and no wires for the radial off-set brackets to be seen.

The Mark II has 3 wires that make up the radiator, 4 wires for the radials, and the rest of the 37 wires are for the radial loop. I see no mast wires and no wires for the radial off-set brackets again.

The segments for the radiator and the near parallel radials should also be close to having equal segment lengths. We can see both models show different segment lengths, maybe by a 2:1 difference if you look close at the little segment junction dots. You can see how this work in the model I posted of the Mark2. Check the details at the bottom of the antenna images for the radiator length and the radial length. This shows the segment lengths I used and they are as close as I can get them. A rule of modeling I always try and follow.

The absence of the mast does not make much difference for a model, but you won't see how bad the CMC might be either if it is not included.

Setting the radials with a direct connection to the radiator, with no stand-off brackets produces a geometry check error as you will see in the image of a Vector 4K model I used to demonstrate.this problem. See the PDF file example I posted below showing the geometry check error message as a result of my removing the off-set brackets from the Vector 4K model, and if you check close you will see the bottom for this example looks very similar to the Vortex models. I had to leave out showing the currents...the error will not let the model scan, so in this case the error is critical.

Homer, do you recall ever having such a problem with one of your homebrew Vectors? I seem to recall we talked about it back in the days.

If you check the Eznec Control Center view for the either of these Vortex images you will see all of the 3 Eznec tuning function tools, Loads, Transformers, and L Networks are all indicating zero 0. This means the function is not being used. I put a black mark beside each item.

Below is a PDF file with my example of the Geometry error and I included the two Vortex images for the Q82 Mark I and Mark II in landscape view (sorry) so I can see more of the images.