Avanti Sigma4: An alternative view point

[bob85]

1

Bob, I know the best we can do to depict AC currents flowing on a wire is to indicate them at some particular point...frozen in time, so-to-speak. But, what determines the direction those arrows point when EzBob plots such an image?

i determine which direction they flow in my minds eye based on what i have read from respected sources and what cebik said was very much possible,
i tried to portray the concept when i drew several antennas and folded the gamma fed dipole,

I think I saw that post also, and thought it was interesting. If the phase idea works with this 1/8 wavelength idea like current flow is reported to work on a 1/2 wave dipole, then the antenna system would necessarily have to waste another 1/8 wave above it on the good phase portion of the element...in order to show cancellation due to opposing forces. IMO, that is why the dipole is depicted to have the currents on both sides of the source flowing in the same direction (in-phase) and hopefully both legs with the same magnitude. And if there is no in-phase flow, then the RF is canceled just like it is inside the coax. If the magnitudes are not equal then we can experience common mode currents of the feed line shield as well.

coax internal currents are always equal, the trouble starts in the world outside the coax when you connect those equal currents to an unballanced antenna on a conductive mast without a balun or choke, w8ji explains the situation well imho,

For a long time I've had this thought - even if the RF from the 1/8 wave segment at the base of a 5/8 wave radiator was canceled somewhat, that its major contribution to the antenna's effectiveness was to raise the 1/2 wave current portion higher up on a longer and higher radiator. I assumed this would show an improvement in maximum radiation...and this is why the 5/8 wave is said to show more gain at a low angle. Notice that I said "...at a low angle," not a lower angle. I was never convinced however, that this small increase in elevation was quite enough to really lower the maximum angle of radiation in a primary lobe. In the modeling I do I most often see changes affecting the higher angled lobes rather than the lowest lobe. I believe it likely works that way in real life antennas too, except to some degree how antenna elevation changes have their affects the lower lobe may be affected a little. In the 18' to 50' range we often see in CB, I doubt this low angle change would be much however.

Bob, I'm surprised you never looked at what is going on at the base of a 5/8 wave antenna. Surely you've had some thoughts about how the 5/8 wave element works.

yes i do have thoughts about how it works, it works poorer than the sigma design for the majority of people,
so i looked at what could effect the 5/8wave adversely that could cause a desert dweller to love em and me to think they are nothing special at all, we have discussed this and i believe i found two possible answers from two different respected sources,

i have not looked at the 5/8wave radiator in any detail because 3rd place does not interest me,


Bob, I don't really know either why the currents are as they appear and you're right about my lack of expectations. I don't make the models to show anything in particular. I'm sure whatever I do has some affects, but my activities in the area of currents are not deliberate or planned. I just try to get the physical dimensions right and keep the Eznec errors from popping up. I figure if the dimensions are close enough, then let Eznec worry about the scientific calculations.

I did fix the model to agree with your argument about mast currents the other day, but I can't honestly say what I did to get those results. When I do a model, I don't plan with currents in mind. I just don't understand enough about currents, direction, or phase to plan that stuff. I'm sure to be very accurate in modeling it is desirable to get currents right...since the whole NEC engine uses pre-determined scientific factors regarding currents to do its calculations.

eddie, when the dimensions are input into a model and the software can handle the unusual tapered transmissionlines ect the currents will automatically be correct,
you understand eznec better than i do, i listened to cebiks warning about trying to get accurate results with the sigma style antenna and read the limitations of nec dealing with transmissionlines formed from differing diameter tubes/segments and not been parallel, the tapered gamma does not help either,

i would distrust any model that shows the vector to have a higher takeoff angle than a groundplane because it does not agree with whats demonstable in our tests,


Yes Bob, you've done an excellent job of getting your experiences out and finding a logical source for the collinear idea and I personally believe that is what makes the Sigma 4 design work like it does.

thanks eddie, you stick with that belief,
i must thank shockwave for his excellent input and mr lorenzo for his cst model,


Well Bob, that leaves me with some very big steps to try and follow. I have to say, I don't think I'll ever be able to satisfy such goals, even if I promise to never mention the J-pole. Personally, I think the J-pole is a mute issue when considering the Sigma4 design.

eddie, you can mention j-poles as much as you like, it makes me laugh,
i hope it makes you laugh when i call the antenna im building the "NAPCO weiter Sprecher "


Bob, you mention your CB band is different from the US. I think it is higher in frequency, right? Why then, back in the day, did you ever consider to making the antenna longer? I would have thought that would be putting me further away from the desired frequency range. Just curious about that.

thats because you are hindered by what you already know eddie,
yes our ch19 is 27.78125mhz fm,
i was 15/16 years old and willing to try anything to make my station talk further than my buddies, id seen while tuning my own sigma and how locals had their tuning settings all over the place yet still got a decent vswr, common sense says they can't all be right,
why on earth would i not try moving something both ways,


There is absolutely nothing wrong with modifying stuff. I admire folks that experiment in life. Among other things, I cut my teeth on modifying a couple of 55' Chev's in my younger adult days. One for street modified, with a 283" small block. I competed successfully and won often in NHRA "C" & "D" Modified Stock classes in the 50's and 60's. I was never satisfied. I could change nothing on the exterior of the engine, drive train, body, or suspension, but I worked midnights under a shade tree on the guts of the business, to run that thing in the high 12's, over 100 mph @ 1/4 mile tracks around Texas. That is nothing with today's technology, but it was hot back then, or at least I thought so as l left a lot of better cars in the rearview mirror. I've always done things that you might call "out of the box" even if I don't see the subject that way. I hate buzz words.

don't get me started on tuning engines and suspension, you will open a whole new can of worms much bigger than the sigma4,

We also see now that Sirio has elected to go longer on the radials, but shorter on the radiator while they claim to have retained all their previous gain and angle advantages compared to their previous Vector 4000. This one is a sleeper too. I've not heard a sole proudly reporting on his New Vector 4000, even though several guys on this forum have one. Bob, you told me that it's still not built well enough for the UK climate. You mentioned that Multimode said something, but I can't recall what. I don't think he had a report however. That is strange that no body in Europe or the US has tried it and reported what the New Vector 4000 design can or can't do? I don't think it was a new design that Sirio discovered, I think they were probably forced, due to antenna failures, to make it shorter somehow and to try and mitigate the bad reputation it has.

i don't know anybody that has tested one against another antenna apart from mack swapping his wolf.64 for the vector,
i do have a buddy here using the new top-one but he has no other vertical to test against at the moment,

do have that in mind even though it is the hardests one to put up and tune. My new mount is close to the house and I can still get up that high safely. I designed it that way for that reason.



I'm impressed by the Gain Master, but there are some exceptions to my stellar reports so far. None exceed the SGM, but I do see a few signals that match it and one today where a guy reported the GM showed him less signal. Bob, it is like summer before last, I'm seeing conditions in terrible shape and I have a lot of static. As our weather becomes cooler and less humid the noise seems to really affect signals and hearing, at least that is what I think. Our recent summer was very dry late in the year so I may be seeing some change that is affecting how the antennas here typically act. This may even be affecting the water table in my area. I'll know more about that when I get the I-10K up if I do that too. My new mount allows me to work those bigger antennas without having to build them and attach them to the mast and then raise all that up.

we are getting the same problems with static here, LOTS of it and it moves from one station to another seemingly randomly, now is not a good time to test antennas with conditions so variable but we must try,
you take it easy with that testing,




73's
Eddie

 

[CDX-007]

Hey Bob, what were the results of Mack swapping his Wolf.64 for the Vector, and do you know where is that post?

 

[bob85]

007, im not sure where mack posted his comments i know he was happy with its performance if not the build quality

 

[CDX-007]

And I'm so pleased with mine (SGM) that I stood outside and stared at it for 20 minutes early this morning, visualizing it 25' higher. :

 

[CDX-007]

Homer...
Do you recall the complaints I got from two customers some years ago that that I often talk about, and maybe even in this thread. They bought 31' foot CTE Saliut models from me. They each made their antennas as long as they could and tuned them. They complained that they talked alright, had a good match, but the receive was no good...

Good luck,

Since I intend on testing one for cone radiation with a field strength meter, and the one I have in it's entirety is a 7/8 Saliut, should I assemble it:

1) As a .82 like the one Shockwave said not to?

2) As a stock 7/8 Saliut?

3) As a newer 3/4 like the latest version of the Vector?

I want to know if the cone does or does not radiate, so I am going to build & test it in order to satisfy my need to know via empirical knowledge.

 

[Marconi]

Since I intend on testing one for cone radiation with a field strength meter, and the one I have in it's entirety is a 7/8 Saliut, should I assemble it:

1) As a .82 like the one Shockwave said not to?

2) As a stock 7/8 Saliut?

3) As a newer 3/4 like the latest version of the Vector?

I want to know if the cone does or does not radiate, so I am going to build & test it in order to satisfy my need to know via empirical knowledge.

I never saw these antenna and I never ordered any more because of the problem I had with em'. Two of the guys complained and the one I knew best would not cooperate in trying to fix the problem.

Maybe you could take Bobs advise and set it at about any length and tune it for best results at a distance. Bob found the longer the better.

Personally, I thought these guys just made their antenna too long, because it was supposed to be tunable for 10,11, and 12 meters. None of the guys ever complained that they could not tune the antenna, two just said they talked OK, but they had no ears. Frankly, that could mean about anything, and I don't know what specifically they experienced. Until I heard Bob's good experience years later, with the same antenna I believe the 31' CTE, I understood they were doing more or less what Bob found to be the best performer, but I can't be sure. I also heard these antennas had the entire length of the bottom section fluted which was said to improve antenna support.

So, regarding your question and the added length over my Sigma4. I always assumed the added length was so you could tune it down in 12 meters.That is all I knew until Bob told me the antenna could be set at any reasonable length and tuned to the desired frequency with the gamma and I think Shockwave confirms that.

I think the instructions for the antenna were useless for good info, but I seem to recall a couple of dimensions that seemed unimportant measurements for sure, and I wondered why they showed those measurements and not the rest of the important measurements.

Ask them.

 

[CDX-007]

Am I the only one who has to keep signing-in every 5-10 minutes?
- It's getting frustrating.

Well, since they have such an incredible test facility, I guess I'll just set it to what's working for Sirio and set to their overall dimensions for their "New Vector 4000". I really just want to check for the cone radiating level compared to the upper ½ wave.

 

[Marconi]

Am I the only one who has to keep signing-in every 5-10 minutes?
- It's getting frustrating.

Well, since they have such an incredible test facility, I guess I'll just set it to what's working for Sirio and set to their overall dimensions for their "New Vector 4000". I really just want to check for the cone radiating level compared to the upper ½ wave.

Did you see the model that Shockwave posted. That shows about as good as you might get aside from using a test chamber, and then I'm not sure the Vector would fit inside that facility. Sirio might have to scale their antenna test back to do their work. That model he posted I would say displays numerous things probably, but unlike my Eznec it also predominately shows the RF pattern and not just the currents magnitude. That said, the whole antenna is noted to be making a large tear drop like lobe with max RF near the center and top all the way to the base with little to no RF shown upward. Bob is right.

Take another look 007.

The way I see it, the cone is radiating in-phase and the RF inside the cone is mostly confined due to reversing currents between the radials and the radiator.

I'm having no problems.

 

[CDX-007]

Did you see the model that Shockwave posted. That shows about as good as you might get aside from using a test chamber, and then I'm not sure the Vector would fit inside that facility. Sirio might have to scale their antenna test back to do their work. That model he posted I would say displays numerous things probably, but unlike my Eznec it also predominately shows the RF pattern and not just the currents magnitude. That said, the whole antenna is noted to be making a large tear drop like lobe with max RF near the center and top all the way to the base with little to no RF shown upward. Bob is right.

Take another look 007.

The way I see it, the cone is radiating in-phase and the RF inside the cone is mostly confined due to reversing currents between the radials and the radiator.

I'm having no problems.

No I haven't seen the model SW posted, could you add a link to that post?

I did find this post during my research and I suppose it is an old, out-of-date post from back when the design wasn't fully understood because it states the bottom ¼ wave doesn't radiate according to testing with a field strength meter.
- I apologize but I haven't been keeping up on reading about the SigmaIV / Vector4000 posts. :blushing:

 

[Shockwave]

CDX, as it turns out the field strength meter is extremely inaccurate in the near field for trying to determine what sections of an antenna are contributing to radiation. Take a simple 1/4 wave mobile whip. The field strength meter is going to be highest towards the top and lowest at the base, even though maximum radiation is from the base. Field strength meters seem to respond to the highest RF voltage and not the highest radiation current. This is one reason why they must be used several wavelengths away for accuracy and also explains my earlier, incorrect conclusion that the base of the Sigma didn't radiate much signal.

Please look at the detailed picture of the radiation currents below shown in CST, courtesy of Sirio. We are not likely to ever see any more conclusive proof that the Sigma / Vector radiates from the cone in a phase that is constructive with the upper radiator. This antenna can be effectively configured to perform as anything ranging from a 1/2 wave over a 1/4 wave to a 5/8 wave over a 1/4 wave. The CST model proves the shielding action of the cone to block deconstructive radiation from the lower 1/4 wave of the main radiator. The cone also provides it's own 1/4 wavelength of radiation in the correct phase.

 

[CDX-007]

Accidental double post

 

[CDX-007]

CDX, as it turns out the field strength meter is extremely inaccurate in the near field for trying to determine what sections of an antenna are contributing to radiation. Take a simple 1/4 wave mobile whip. The field strength meter is going to be highest towards the top and lowest at the base, even though maximum radiation is from the base. Field strength meters seem to respond to the highest RF voltage and not the highest radiation current. This is one reason why they must be used several wavelengths away for accuracy and also explains my earlier, incorrect conclusion that the base of the Sigma didn't radiate much signal.

Please look at the detailed picture of the radiation currents below shown in CST, courtesy of Sirio. We are not likely to ever see any more conclusive proof that the Sigma / Vector radiates from the cone in a phase that is constructive with the upper radiator. This antenna can be effectively configured to perform as anything ranging from a 1/2 wave over a 1/4 wave to a 5/8 wave over a 1/4 wave. The CST model proves the shielding action of the cone to block deconstructive radiation from the lower 1/4 wave of the main radiator. The cone also provides it's own 1/4 wavelength of radiation in the correct phase.

Thanks for the reply Shockwave, and how long is the one you used to compare to the SGM?

How can I get the full active simulation of the CST model?

 

[mackmobile43]

Hey Bob, what were the results of Mack swapping his Wolf.64 for the Vector, and do you know where is that post?

I've had reports of being heard at 50 miles via a dx message from Texas lol but I could not hear them and 35 was the best I could do with the wolf.64 on the same pole.

 

[CDX-007]

I've had reports of being heard at 50 miles via a dx message from Texas lol but I could not hear them and 35 was the best I could do with the wolf.64 on the same pole.

Thanks for the reply, and that's a good report in comparison to the Wolf .64.

 

[BOOTY MONSTER]

shockwave thats very interesting looking . could you possibly explain in lay-mens or simpleton terms what the different colors mean ? is this something you modeled up yourself ?

thanks