New Vector model using tubing and tapper

[Marconi]

Just finished modeling the Vector where I used actual wire dimensions and tapper for the radiator from top to bottom and it still shows good gain at low angles. I still have to tapper the radials and try an make the hoop in a circle. I used Henry's model in this effort.

And they said maybe it could not be done and still show some gain.

http://www.worldwidedx.com/members/...el-using-tapper-actual-tubing-dimensions.html

 

[bob85]

eddie,
if you look at what cebik says about gammas in his tales and technicals regarding gamma calculators and models plus what he told me about it been difficult getting accurate models of the sigma and what nec says about segment junctions, its pretty clear that nec will have multiple problems with the sigma4 style antennas,

you have to deal with the tapered transmissionline formed by the radials having unequal junctions, differeing diameter to the monopole and been tapered,
you have a round hoop interconnecting the radial ends,
nec can have problems even with conventional gammas, not only is the sigma gamma not parallel to the element its feeding it is also a tube style and not a gamma rod with lumped capacitance,

i think you are getting closer than the models we have seen so far but i don't have a clue how you are doing it within the limitations of eznec

 

[Marconi]

eddie, if you look at what cebik says about gammas in his tales and technicals regarding gamma calculators and models plus what he told me about it been difficult getting accurate models of the sigma and what nec says about segment junctions, its pretty clear that nec will have multiple problems with the sigma4 style antennas,

Bob, I'm not discounting what Cebik and others say, and I don't consider my models accurate. Eznec is just too complicated for me and these guys know best. My challenge was to see if I could get closer to the specs and still have the model show some gain, when it was said "it can't be done." I'll no doubt find problems on down the line, but just because somebody says it can't be done only causes me to pause, not stop...like others have done.

you have to deal with the tapered transmissionline formed by the radials having unequal junctions, differeing diameter to the monopole and been tapered,

I did model with no junctions in the radials for the first three elements of the radiator at the bottom. I also made the first, second, and third elements the spec diameters so the only difference in the radials and the radiator, in that area, would be the diameters, and the one junction near the top of the hoop. This is not to say this doesn't matter, so that may be an issue. I did check the specs against my compromise connection idea and I saw a very little difference, so my model presented remainds at what the specs call for and the one junction. This is also why I choose not to taper the radials, and obviously that too can make some difference. This effort was done because you brought the idea to everyone's attention, while we were trying to figure out why the model would not show gain using the specified tubing diameters.

you have a round hoop interconnecting the radial ends, nec can have problems even with conventional gammas, not only is the sigma gamma not parallel to the element its feeding it is also a tube style and not a gamma rod with lumped capacitance,

i think you are getting closer than the models we have seen so far but i don't have a clue how you are doing it within the limitations of eznec

Bob, I just tried as best I could to make the antenna to specs where I could and compromise as little as possible, and make it look as close to the real antenna as I could. I have no idea how NEC interprets what connections are good and those that are not. I am able to deal with the error messages that Eznec produces however, and this model shows none. I understand that the sharp angle at the bottom of the Sigma can also present problems. I'm also sure that if I could add the gamma match to the model, that too would make some difference or prove to be impossible.

I have messed with my 1/4 wave GP models in many ways trying to emulate mis-matches and asymmetrical imbalance in the construction and results. I find, that unless the change is really dramatic there is most often very little change in the antenna pattern modeled, the angle and the gain seem to be affected very little. The obvious problems noted were in the source impedance and SWR, and I don't know what the truth in that technical matter really is. I've heard for years that within reason...the match really makes little difference to the ultimate radiated pattern. It seems to matter however, how your radio works and if the radio responds as it should...and if not it will likely reduce the input power and thus the RF will suffer. I don't know if or how Eznec handles this consideration.

I've tweaked some of my other models to see modest increased in gain, but I've never been able to make the angle change dramatically if at all...except when modeling the 5/8 wave and I think that antenna has a tipping point close to the 5/8 wavelength where something special happens.

The only tweaking I did with the Sigma 4, in this case, was to tweak the ultimate length of the top element just to see a better resonance, and then the SWR went down from 1.6 to 1.2 and the gain increased from 4.7 to 4.68 dbi...while the angle and pattern remained about the same. In other words I didn't do anything special, I just put the dimension data in as I saw it and that is what I got. I also raised the antenna higher than Henry's, he had his most recent model on the ground.

 

[Marconi]

double post.

 

[bob85]

lol, don't tell eddie he can't do something:sneaky2:,
i commend you on your efforts with modeling the sigma design especially given that you so far have not seen the advantage the sigma design demonstrates over groundplanes at your location which would lead average joe to give up,

i don't understand nec but what cebik told me made me look at what some of the gurus had to say about different parts of the antenna and came to the conclusion that the tapers, unequal diameters, unequal segment lengths, sharp folds, round hoop plus the angled tubular gamma could all cause errors in nec and i don't know how to work around those issues or how much they will effect the results,

i would like to see what your nec model says happens when the monopole is extended to about 30ft with 90" radials,
ezbob predicts that extending the monopole will increase distance between the two current maximas and skew the phase relationship in the lower 1/4wave which may cause the results we see in field tests

 

[Marconi]

lol, don't tell eddie he can't do something:sneaky2:,
i commend you on your efforts with modeling the sigma design especially given that you so far have not seen the advantage the sigma design demonstrates over groundplanes at your location which would lead average joe to give up,

i don't understand nec but what cebik told me made me look at what some of the gurus had to say about different parts of the antenna and came to the conclusion that the tapers, unequal diameters, unequal segment lengths, sharp folds, round hoop plus the angled tubular gamma could all cause errors in nec and i don't know how to work around those issues or how much they will effect the results,

i would like to see what your nec model says happens when the monopole is extended to about 30ft with 90" radials,
ezbob predicts that extending the monopole will increase distance between the two current maximas and skew the phase relationship in the lower 1/4wave which may cause the results we see in field tests

Bob, I sure wished I had the energy to continue my antenna work. I missed this whole summer, except I did put my A99 up on a 10' pole and proved to myself that my radios do not provide very good RX signal report readings. I suspect that you know that from experience, what can happen. I have lost a lot of confidence in the reports I put together summer before last. Boy how time goes by...when you're having fun.

I think I did some of the longer and shorter radiator ideas with my first modified effort using Henry's original model. I think I emailed you something about what I was seeing, but I'm not sure what or if I sent anything along.

I think such results won't impress you when making the radiator longer and leaving the radials alone. I think I found the same dismal results increasing the length of the radials too. I will try to do the first part as you indicate, but I found the gain results went down instead of getting better. In fact, that model showed more gain to be had making the radiator shorter to about 26.5' I think, but I don't know why. Sort of like Sirio has done with the New Vector. I do recall something about that model concerned me though. Maybe it was the pattern that did not look right. I'll check and see what I kept of the effort or maybe do it again.

I will also note, that my model where I insulated the mast from the antenna a few inches also showed a somewhat noticeable drop in gain for some reason, and I'm not sure without checking back how this affected the angle if at all. That really surprised me too.

Since I think I have a better model with the Sigma 4 now, I will check that out and send you the results...or I might wait and do it after I fix the New Vector model.

The output for the wires and the currents is quiet long now, so I will have to see what is the best way to get you the results. Do you know someone convent that has Eznec 5 or better, where you could use the actual file? These files so far are small compared to the results generated.

Do you recall the PDF files that I sent you soon after I got the Eznec Demo version. I know you were able to handle them, but were they good with the details or could you print them making them easier to compare if I sent you a lot of stuff to look at?

You let me know what sounds best. I don't want to send a lot of stuff that wastes your time.

Eddie

 

[bob85]

i understand the difficulties in getting good signal reports especially as the conditions are unstable with the sun waking up, even with our normally stable fm signals we get fluctuations from time to time, something as simple as an airplane flying over causes my buddy at the other side of the hills signal to wave about as much as much as plus 2 s-units and down to zero, when the plane passes over me we get the same effect again,

you could be right about me not been impressed with the model and extended monopoles but increased signals are what we see in tests, the only two things that come to mind are changing the gain ( unlikely imho ) or tweaking the takeoff angle the radiation angle or possibly a bit of both,
the sirio has 4 radials and a thinner monopole so id expect it to be a little longer than a stock sigma when tuned to the same frequency, real tests show that extending the monopole too far reduces distant signal strength, what does not tally with eznec is exactly how long you can go before you start going backwards,

i don't know anybody local with nec at all, some locals build antennas but as one of my antenna homebrewing ham friends said he don't care how they work so long as he make the contacts,
yes i think i could see the models, the pics in your album look larger and easier to see