Hello Henry. I wouldn't expect Mr. Lewallen to be anything but subjective in his response about his own software, unless he had actually modeled and made comparisons for the Vector/Sigma4 that was modified.
To eddie:
Subjectivity about eznec has nothing to do with two different models?
If you i interperted you rigth and you do have "sarcasme" about his objectivity than your wrong. (again Englisch is not my best abillity.
Eznec is used all over the world, Military,proffesional broadcast, Nasa etc..
I guess i am one of the more simple type of usereand with permission i would place most of us here under that number.
The designer has no advantage of telling "no-truth" stories as if they would come out it would fall apart.
Escpecially programms like Eznec value there "limitations" as with them figures are "not real"..
Just imagine if the "word" got out that it is "not" reliable...They would be out of buisness very soon.
There is a entire help section wich describes the limitations of Eznec...
I think that speaks for it self.
Dr. Cebik would have a benefit of "positive" speaking about Eznec as he had "models" for sale in the past.
Now, you get my point?
(if the point needed to be made, i interperted it as sarcasme pehaps i misunderstood!)
I hope the above gives you insigth in why one would "tell the truth"about anything while he has a personal intrest (provite).
You told us that you modeled using thin wires out of convenience. I have no problem with that, if the use of wires vs. correct tubing diameter and taper---does not ill-affect the results too much either way. It would be nice if you could model using thin wires and not have to mess with thicker tubing and taper. Am I assuming correctly, that when you used the thin wires rather than tubing, that the element lengths all ended up being short, unless they were adjusted for the same resonance as the tubing and tapered elements?
To eddie:
Please forget about the first model.....It was done in a couple of minutes just to get started and see if it could be done..
Element diamter has influence on all.
You can not just use a set of wire thickness...When one rebuildts a antenna they should use the same element diameter.
Yagi/Quad designs with measurments without element diameter are meaningless
(is that written correct..? i mean not usefull lol..)
I don’t know which Vector you used to approximate your measurements, but you told me the radiator was about 24’ feet long using thin wire. That is considerably shorter than my Sigma 4 and for sure shorter still compared to the original Vector 4000, yet your model shows resonance low in frequency to 26.950 mhz. I don’t get that, because in that situation the resonance should have gone up using shorter and thinner wires. On the other hand you indicate the radials were 108” long which is much longer than my Sigma4 @ 90.5” and maybe longer than the older version of the Vector that Shockwave may have used. So I ask, in your opinion is it possible that frequency is primarily affected by a change in resonant length of the radials and less so when adjusting the radiator length? I think Bob tells a story about his Vector, where the tip collapsed down into the next section and it didn’t seem to make a difference.
To eddie:
First about resonance.. it "isnt" that intresting as you can match a antenna.
And will radial length influence "resonance" frequency...well take a look at a groundplane..
with or without radials will that influence in either SWR ..yes.
One can think of a radiator and resonance as where there are purly "real" ohms.
Will that point of "real" ohms be different with different radials ...yes.
Therefor radial length will infuence aswell.
Were talking about radials now..but the antenna uses (as i see itnow,the skeltont sleeve princable, my personal knowledge of this princeble lacks..But we all have heard it atcs as a matching section
As it is said...matching section so yes that will infuence
PS intresting reading about the sleeve:
http://ceta.mit.edu/PIER/pier58/07.0509031.Li.G.pdf
I also read that SW indicates he made changes which are noted to have raised the resonance to 27.200 mhz with his adjustments. If I measured SW’s wires chart, that Bob posted, correctly, he made the radiator longer to 25.26’ feet using the same wire diameters. This should have lowered the frequency and that is not what is indicated.
SW’s chart also indicates he made the radials 3” inches shorter @ 105” compared to your radials @ 108”. Here again, we see this tending to lower the frequency, as it should, even while making the radiator longer. Does this also suggest that the resonance for this antenna design is primarily affected by the length of the radials and not the top element? Homer questioned all this a while back, so maybe he can shed some light on this idea if he got to do his modifications to his homemade Vector. Homer, how say you?
To Eddie,
Resonant frequency isnt primarily changed with radial length also the radiator itself has a large influence..also everything else as heigth/obstacles and the enviroment/material used for antenna etc.
Also where the antenna is placed perhaps a google search on "superconductors" in relation to antennas can give some insight. In theory it would be possible to make "perfect small antenna"
Henry you also told us that using a square radial hoop vs. a circle made no difference, but have you checked to see if using thin wires that were or were not adjusted for resonance vs. tapered tubing---makes any difference in the model results that are worth noting?
To eddie:
Dont understand thequestion...But if your asking again about wire thickness and influence than yes.
How did you get your model to resonance taking measurements from an antenna with thick tubing without converting for thinner wires, were you just lucky?
To eddie:
Eznec allows you to change diameter..by running a "swr" measurment you can see where best matching is possible. If for instance swr is set at 26mhz you can rescal to 27 mhz
This will also convert diameter. However you could reset those figures and seewhat the antenna does.
In the text of your Vector file it notes the impedance being easy to match with a gamma match, so I assume you did not included a matcher at the bottom of the model. Your bandwidth chart indicates ZO impedance at 34 ohms with a very low SWR. If that is the case then the antenna is very close to a resonant 1/4 wave with a suitable ground plane and IMP that is what we might expect for a 3/4 wave radiator. I agree this makes the antenna perfectly suitable for a gamma device. What would you think happened to the value of Zo after SW changed the length of the radials and the radiator?
To eddie;
Ofcourse values will changes, however as mentioned a perfect 50 ohm matching is nice. But you can match a almost anything...
A gamma-match is frequently used for matching impedances between 20-50ohms.
Before the antenna is thus far off you would have to made large changes.
Normaly, if you design for example a yagi with a 10 ohm impedance it would have a small bandwidth.
A often used "trick" is to higher the impedance as it is possible to achieve a larger bandwidth.
Can you describe where the source is that shows this Zo impedance on your original model? I assume it has to be at some point above the hub on the first element where we might expect to see the gamma tap point. I see a small bump a little above the hub. Is that the feed point, and how does that get there? I don't see it noted in the wires chart.
To eddie:
The source can be placed everywhere you want in my files it is where you mention.
(one should keep in mind the limitations given by eznec).
The source is placed using another "screen" on eznec.
To eddie:
I would highly recommand you to purchase eznec...and see for your self it is a valuable assist when one likes to deal with antennas.
Futher more, ofcourse all computer programmas cant predict the exact figures..as we all have different surroundings.
But it will tell you what should be "best' for overall uses.
Please dont forget that the first thing ahuman ear is acapable of hearing as a difference is about>2dB.
Eznec will be more accurate than that.
A honest comparisment can be made with Eznec, just changing antennes and testing for a while the difference is not the way to go...I do understand you get a better feeling with one or the other.
But unless you have two antennas indentical feed heigth several wl apart and can compare than both at the same time again results will be different with different users.
I hope it helped?
Kind regards,
Henry
To eddie:
Subjectivity about eznec has nothing to do with two different models?
If you i interperted you rigth and you do have "sarcasme" about his objectivity than your wrong. (again Englisch is not my best abillity.
Eznec is used all over the world, Military,proffesional broadcast, Nasa etc..
I guess i am one of the more simple type of usereand with permission i would place most of us here under that number.
The designer has no advantage of telling "no-truth" stories as if they would come out it would fall apart.
Escpecially programms like Eznec value there "limitations" as with them figures are "not real"..
Just imagine if the "word" got out that it is "not" reliable...They would be out of buisness very soon.
There is a entire help section wich describes the limitations of Eznec...
I think that speaks for it self.
Dr. Cebik would have a benefit of "positive" speaking about Eznec as he had "models" for sale in the past.
Now, you get my point?
(if the point needed to be made, i interperted it as sarcasme pehaps i misunderstood!)
I hope the above gives you insigth in why one would "tell the truth"about anything while he has a personal intrest (provite).
You told us that you modeled using thin wires out of convenience. I have no problem with that, if the use of wires vs. correct tubing diameter and taper---does not ill-affect the results too much either way. It would be nice if you could model using thin wires and not have to mess with thicker tubing and taper. Am I assuming correctly, that when you used the thin wires rather than tubing, that the element lengths all ended up being short, unless they were adjusted for the same resonance as the tubing and tapered elements?
To eddie:
Please forget about the first model.....It was done in a couple of minutes just to get started and see if it could be done..
Element diamter has influence on all.
You can not just use a set of wire thickness...When one rebuildts a antenna they should use the same element diameter.
Yagi/Quad designs with measurments without element diameter are meaningless
(is that written correct..? i mean not usefull lol..)
I don’t know which Vector you used to approximate your measurements, but you told me the radiator was about 24’ feet long using thin wire. That is considerably shorter than my Sigma 4 and for sure shorter still compared to the original Vector 4000, yet your model shows resonance low in frequency to 26.950 mhz. I don’t get that, because in that situation the resonance should have gone up using shorter and thinner wires. On the other hand you indicate the radials were 108” long which is much longer than my Sigma4 @ 90.5” and maybe longer than the older version of the Vector that Shockwave may have used. So I ask, in your opinion is it possible that frequency is primarily affected by a change in resonant length of the radials and less so when adjusting the radiator length? I think Bob tells a story about his Vector, where the tip collapsed down into the next section and it didn’t seem to make a difference.
To eddie:
First about resonance.. it "isnt" that intresting as you can match a antenna.
And will radial length influence "resonance" frequency...well take a look at a groundplane..
with or without radials will that influence in either SWR ..yes.
One can think of a radiator and resonance as where there are purly "real" ohms.
Will that point of "real" ohms be different with different radials ...yes.
Therefor radial length will infuence aswell.
Were talking about radials now..but the antenna uses (as i see itnow,the skeltont sleeve princable, my personal knowledge of this princeble lacks..But we all have heard it atcs as a matching section
As it is said...matching section so yes that will infuence
PS intresting reading about the sleeve:
http://ceta.mit.edu/PIER/pier58/07.0509031.Li.G.pdf
I also read that SW indicates he made changes which are noted to have raised the resonance to 27.200 mhz with his adjustments. If I measured SW’s wires chart, that Bob posted, correctly, he made the radiator longer to 25.26’ feet using the same wire diameters. This should have lowered the frequency and that is not what is indicated.
SW’s chart also indicates he made the radials 3” inches shorter @ 105” compared to your radials @ 108”. Here again, we see this tending to lower the frequency, as it should, even while making the radiator longer. Does this also suggest that the resonance for this antenna design is primarily affected by the length of the radials and not the top element? Homer questioned all this a while back, so maybe he can shed some light on this idea if he got to do his modifications to his homemade Vector. Homer, how say you?
To Eddie,
Resonant frequency isnt primarily changed with radial length also the radiator itself has a large influence..also everything else as heigth/obstacles and the enviroment/material used for antenna etc.
Also where the antenna is placed perhaps a google search on "superconductors" in relation to antennas can give some insight. In theory it would be possible to make "perfect small antenna"
Henry you also told us that using a square radial hoop vs. a circle made no difference, but have you checked to see if using thin wires that were or were not adjusted for resonance vs. tapered tubing---makes any difference in the model results that are worth noting?
To eddie:
Dont understand thequestion...But if your asking again about wire thickness and influence than yes.
How did you get your model to resonance taking measurements from an antenna with thick tubing without converting for thinner wires, were you just lucky?
To eddie:
Eznec allows you to change diameter..by running a "swr" measurment you can see where best matching is possible. If for instance swr is set at 26mhz you can rescal to 27 mhz
This will also convert diameter. However you could reset those figures and seewhat the antenna does.
In the text of your Vector file it notes the impedance being easy to match with a gamma match, so I assume you did not included a matcher at the bottom of the model. Your bandwidth chart indicates ZO impedance at 34 ohms with a very low SWR. If that is the case then the antenna is very close to a resonant 1/4 wave with a suitable ground plane and IMP that is what we might expect for a 3/4 wave radiator. I agree this makes the antenna perfectly suitable for a gamma device. What would you think happened to the value of Zo after SW changed the length of the radials and the radiator?
To eddie;
Ofcourse values will changes, however as mentioned a perfect 50 ohm matching is nice. But you can match a almost anything...
A gamma-match is frequently used for matching impedances between 20-50ohms.
Before the antenna is thus far off you would have to made large changes.
Normaly, if you design for example a yagi with a 10 ohm impedance it would have a small bandwidth.
A often used "trick" is to higher the impedance as it is possible to achieve a larger bandwidth.
Can you describe where the source is that shows this Zo impedance on your original model? I assume it has to be at some point above the hub on the first element where we might expect to see the gamma tap point. I see a small bump a little above the hub. Is that the feed point, and how does that get there? I don't see it noted in the wires chart.
To eddie:
The source can be placed everywhere you want in my files it is where you mention.
(one should keep in mind the limitations given by eznec).
The source is placed using another "screen" on eznec.
To eddie:
I would highly recommand you to purchase eznec...and see for your self it is a valuable assist when one likes to deal with antennas.
Futher more, ofcourse all computer programmas cant predict the exact figures..as we all have different surroundings.
But it will tell you what should be "best' for overall uses.
Please dont forget that the first thing ahuman ear is acapable of hearing as a difference is about>2dB.
Eznec will be more accurate than that.
A honest comparisment can be made with Eznec, just changing antennes and testing for a while the difference is not the way to go...I do understand you get a better feeling with one or the other.
But unless you have two antennas indentical feed heigth several wl apart and can compare than both at the same time again results will be different with different users.
I hope it helped?
Kind regards,
Henry
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