Modified Vector 4000

[bob85]

Eddie, both your models look ballanced to me,
unless in looking at the model wrong one is terminated with a resistor across the far end of a 1/4wave line while the other is an open circuit 1/4wave line,
both been a ballanced situation,

in the full antenna one side is connected to air wile the other sees the end impedance of the radiator, an unballanced situation, that unballance causes the stub of a j-pole to radiate with cmc,



it boils down to can you unballance the model with the correct magnitude of unballance after you remove the upper radiator & can eznec antenna model ( not TL model ) show radiation due to unballanced lines,

or do you need a real TL model in nec to see radiation from transmission-lines,

try turning it upside down & connecting/disconnecting the radiator to ground through a resistor about the end impedance of the radiator, lets guess at 600-1000ohms for a fat tube 1/2wave,
that should unballance it.

its easy for me to ask you to try something but i have no idea what's involved at your end Eddie.

 

[Marconi]

Thanks for having a go Eddie,

if you look again at what Donald said, it may not be the match but getting the cone the right length that minimises cmc,

its not the match,

No problem Bob. I don't remember where I saw Donald say his 0.82 VHF antenna did not need a CMC fix, but you could be right...I read him wrong. I just remembered that I recently modeled his ides based on a conversation he had with Homer.

BTW, I didn't do anything to the cone radials when I made his model. I started using a 0.75 wavelength model. That model showed a little CMC tendency, so I was expecting to see his longer 0.82wl idea do the same.

im in no position to say Henrys model is wrong because i don't know how nec works with regards to how the resistors are connected,
to me it looks like a resistive load connected directly across the end of a 1/4wave transmission-line,

if that is a literal depiction of resistors connected across the end of a transmission-line it won't cause radiation due to cmc on a 2 wire transmission-line,
all you would see is radiation due to the conductors not been parallel, which won't be much at all,

Well, that is why I tried doing both ideas above and I didn't see much radiation from either model, with or without the resistors at the top.

 

[bob85]

Eddie, when we say .75wave or .82wave we are guestimating the antennas electrical length,

its not a piece of wire in free space, its a fat fast taper tube who's electrical length is determined not only by its own electrical characteristics in isolation,
but also by the radial sleeve around the lower 1/4wave which electrically shortens the radiator/raises the radiators resonant frequency,

an electrical .75wave will be physically longer than you expect with this antenna,
how much longer i don't know,

it could be that the best length is .75wave electrical, you just end up longer with a tape measure.

 

[Marconi]

it boils down to can you unballance the model with the correct magnitude of unballance after you remove the upper radiator & can eznec antenna model ( not TL model ) show radiation due to unballanced lines,

or do you need a real TL model in nec to see radiation from transmission-lines,

Thus far I have been using only FS models so I can keep a notice on the Average Gain for the model. Helps me tweak without looking a bunch of details and having to try and remember the previous results

I only know how to add a coaxial FL to a Real Earth model using a wire similar to the mast that I set to the diameter of the coax used. Then I use the feed line tool to create the feed line details and connections to the feed point routing it as necessary.

I'll have to think on the idea of turning the antenna up-side-down.

Bob did you look close at the red line current pattern differences in the models I just posted? I didn't say anything, but I found a difference in my model vs. Henry's, and I had the thought that might be what you were hoping to see since I know you are looking at this stuff really close.

 

[Marconi]

Eddie, when we say .75wave or .82wave we are guestimating the antennas electrical length,

its not a piece of wire in free space, its a fat fast taper tube who's electrical length is determined not only by its own electrical characteristics in isolation,
but also by the radial sleeve around the lower 1/4wave which electrically shortens the radiator/raises the radiators resonant frequency,

an electrical .75wave will be physically longer than you expect with this antenna,
how much longer i don't know,

it could be that the best length is .75wave electrical, you just end up longer with a tape measure.

Well Bob, that is a good point. Yes the elements are guesstimates at best. For various reasons I do not use tapper very much and everybody has told me that my version of Eznec will not work using tapper.

I started by using Donald's calculator factor that he mentioned to Homer, 9212 / frequency. It did not seem to me to be as close as I thought it should, so I figured it was due to different tubing diameters and mix of lengths...which did not come up in the discussion. I have learned that such details seldom ever come up. So, I did some guessing and I figure Homer would be doing about the same thing...if he was to build a new Vector.

Bob I also use my tuning techniques to get my models to show a good match in order to use the SWR bandwidth feature, among other performance results. So a little difference here and there will be compensated for in the process.

 

[bob85]

Donalds antenna is a little different than ours at 27mhz,
his tube diameter vs wavelength ratio is different ( fatter tubes ) & he sites them far above ground relative to wavelength,

I would not worry too much about the full antenna model including the effects of cmc due to unbalance at the top of the cone, based on eznec antenna models ( not TL ) do include radiation due to cmc giving some small gain in the direction of the short leg,
or that's my understanding from what I have read,

I'm more concerned with showing the radiation due to unbalance when modeling the lower 1/4wave in isolation,

the radiation me and Donald are talking about only manifests when there is unbalance at the top of the cone,
radiation stops when you remove the upper 1/2wave because the unbalance goes away, top of radials & cone see the very high impedance of air,

how can you expect to see anything but tiny radiation due to none parallel conductors if the line is balanced when neither coax nor ladder line radiate with the same loads as depicted in the models, that been open circuit and a resistive termination at their far ends ?

match does not matter, balance does,

can somebody/anybody out there please show me the error in my transmission-line logic,
the only way i can make transmission-lines radiate is unbalance them.

I just don't know how you create the unbalance by loading only the top of the monopole while leaving the top of the cone open to air in eznec.

Thank's..

 

[bob85]

i see the resistive loaded model has more current than the open circuit Eddie if that's what you mean.,

it should be different depending on the length of line,

an open circuit 1/4wave looks like a short circuit from the source end,
whereas the resistor loaded 1/4wave will invert whatever impedance is presented at the top of the line unless the resistive load equals the characteristic impedance of the line its terminating.

 

[Marconi]

Bob, I decided to try and tweak the model to as near to a perfect match as I could.

The losses in gain are now very near those of Henry's model.

 

[bob85]

Eddie,
if that was a real transmission-line all you would be looking at with that resistive termination is a line with low vswr that radiates a little due to the lines not been parallel,

that seems to be what the model shows,

there can't be radiation due to unbalance because its not unbalanced,
its a 1/4wave tapered line terminated with a dummyload.

 

[HomerBB]

When I revisit the V4k, it will be a 2m version, and possibly later a 6m.
When the 2m version is made the vertical radiator will be 1/2" copper tube end to end, no taper, and based on the 9212/Mhz formula. The radials and ring will be exact 1/4 wave of center frequency - 146.52 Mhz.
One of the items I need to sort out is the preferred dimensions of the gamma match.

I have not yet settled on the 6m physical materials nor dimensions.

The crude experimental 2m V4k I have up now is not optimum to the frequency I want, but is working quite well, whatever significance that may have ... it is tuned lower than my desired 146.52 Mhz being right at the upper edge of my 2.1:1 VSWR curve.

 

[bob85]

Homer,
new style vectors have suddenly become more popular around here, everybody that put one up has better results than whatever its replaced, 1 snapped & 1 bent already so it won't last,
even i got fed up with fixing mine and i like messing with antennas,

I want to experiment with Henry's idea that adding radials to my sigma will increase signal at distance,
keeping my eyes open for a suitable lump of aluminium to get machined into a radial hub so i don't have to drill the antenna for something i may decide to remove,

 

[HomerBB]

@bob85
I strengthened my homebrew the 3rd one around.
Mine were all homebrew. The first a Sigma IV, the 2and a V4k, which bent over pretty quickly. The final 11m was the improved V4k.
I never bought one. The only one I have now is the 2m.
I removed the end hat wires and lengthened it to 9212/Mhz. And I removed the white wire and put in a gamma.

 

[Marconi]

Homer,
new style vectors have suddenly become more popular around here, everybody that put one up has better results than whatever its replaced.

Well Bob, at least you guy's still have some CB business over there.

R&L Electronics is fully Ham sells now.
Bells has a few Sirio products, but no Vector.
Coppers Electronics doesn't show but a few Sirio products and no Vector.
Sirio Shop still shows a few CB products nothing like they use to though.
Gigaparts only mobile CB stuff anymore.

 

[bob85]

That does surprise me Eddie, in the land where cb started its on its way out,
not many cb shops here either, more people buy from ebay than drive the 50+ miles to knights.

 

[Marconi]

I was hoping you were seeing things different. It was fun while it lasted.