An antenna experiment that Freecell once told me about.

[Marconi]

Shockwave, here is my idea for your model using a wide loop. The height is 36' feet to the hub, and the top of the radials are 6.69' long and 3.3' feet from the radiator which is 29.7' long which I think is .82 wavelength.

I placed the pattern over my Sigma4 Stock model at 36' to the hub.

View attachment Shockwave's wide loop Vector.pdf

 

[Shockwave]

Shockwave, here is my idea for your model using a wide loop. The height is 36' feet to the hub, and the top of the radials are 6.69' long and 3.3' feet from the radiator which is 29.7' long which I think is .82 wavelength.

I placed the pattern over my Sigma4 Stock model at 36' to the hub.

View attachment 8119

Marconi, that model demonstrates the limitations with widening the angle very well. Once you begin exposing more of the first 1/4 wave on the vertical radiator, gain on the horizon goes down while gain in the 40 degree range goes up. That also happens ten fold once you sweep the radials out at 90 degrees or down on a 45.

It should also be pointed out a lot of this work is difficult and easily led astray. It's a labor of love to try and find any way to improve antennas and I'm by no means perfect. Case in point was following through with Avanti's suggestion in the patent that a wider angle would produce improved gain. You saw I built the antenna and even had it tuned to the point it led me to believe there were improvements as I once reported.

In the long run, the idea failed and the discrepancy in the field tests were traced back to deficiencies in the receiver being used to peak the gain. While gain in transmit is reciprocal to gain in RX on nearly all antennas, troubles can easily arise when you discover the input impedance on nearly every HF receiver is far from 50 ohms. That makes a huge difference when tuning for gain in what you assumed was a 50 ohm match. It took a network analyzer and some receiver work to correct that issue.

 

[HomerBB]

Homer, The dimensions are all based on achieving a 1/4 electrical wavelength in the cone structure that physically lines up with the bottom 1/4 wave on the main radiator. Both EZNEC and CST demonstrate peak gain occurs when this condition is met. CST does the most dramatic job of displaying this when you see both of these currents reaching 90 degrees or 1/4 wavelength but you can see this affect with EZNEC too.

Okay. I would need to model an antenna before building it, or get solid dimensions from someone who has.

 

[HomerBB]

The only thing I knew for sure prior to now about inverting unbalanced ground planes is that it had been common practice in reducing skywave interference on low band for decades.

Sweet clarification.

I think you've also taken what I said about other peoples models and the high angle of radiation out of context. My findings on the radials are if you sweep them down like a normal ground plane, the result is an extremely high primary lobe around 40 degrees at typical mounting heights. If you want your model to reflect the situation I discussed then build the antenna like I was discussing. That would be a 3/4 wave ground plane with radials anywhere from 45 to 90 degrees.

I made one of these once, except it was 5/8, but I fooled around and mounted it right side up . . . I had no idea it may almost have had that pesky 40 degree lobe on the run.

Seriously, SW, do you mean down swept radials? or the upward cone like the v4k?

 

[Shockwave]

Sweet clarification.

I made one of these once, except it was 5/8, but I fooled around and mounted it right side up . . . I had no idea it may almost have had that pesky 40 degree lobe on the run.

Seriously, SW, do you mean down swept radials? or the upward cone like the v4k?

The 5/8 wave antenna doesn't have enough inverted radiation currents at the base of the vertical whip to make the 40 degree secondary lobe stronger then the lower primary lobe.

Therforefore it is not a benefit to sweep the radials upward. As the vertical radiator gets to 3/4 or 7/8 wave the inverted base currents are much stronger. Unless the radials sweep upwards like the Sigma, those currents make a huge 40 degree lobe.

 

[HomerBB]

Thanks SW.
I once was taught when doing public speaking that the material had to be broken down to terms so simple the least educated in the audience would understand.

I am a natural born simpleton and asking specific questions dialed into specific points prevents me from assuming things and coming up wrong.

You are a patient man.

 

[Marconi]

Marconi, I'm not looking to argue. You'll notice before the part you quoted I clearly said "We have been working on ways to stack a pair, add null fill and beam tilt. One method does indeed involve inverting the lower antenna to hang it upside-down." When I say "We may also begin recommending stations using a single antenna at extreme elevations, side mount the antenna upside-down." Of course that all hinged on what the modeling results showed.

Yep, words can be confusing and misleading sometimes, even my own. Arguing is OK as long as it is done with respect and consideration for another point of view, but I have questions to ask and statements to make that seldom come up in discussions, and when it does, it tends to inflame some. I don't deliberately intend to be mean in asking, but I know it appears that way sometimes...as I get excited,others tend to get excited in being questioned.

The idea hadn't even occurred to me until I saw my free space model indicating some degree of beam tilt so cut me some slack for being optimistic here. I appreciate your concern for my customers however, it's not justified since I wouldn't recommend anything until it were fully tested. The only thing I knew for sure prior to now about inverting unbalanced ground planes is that it had been common practice in reducing skywave interference on low band for decades.

I'll be looking for this beam tilt too, so let me ask, do you mean a tilt below the horizon, or are you describing something else up much higher in the pattern?

I'm still waiting for someone to post some evidence in all this history of a upside down ground planes. I'm sure a few are out there looking this up as we speak.

I think you've also taken what I said about other peoples models and the high angle of radiation out of context. My findings on the radials are if you sweep them down like a normal ground plane, the result is an extremely high primary lobe around 40 degrees at typical mounting heights. If you want your model to reflect the situation I discussed then build the antenna like I was discussing. That would be a 3/4 wave ground plane with radials anywhere from 45 to 90 degrees.

Well that's good to know. All I've heard up to now is that some RF expert guys commented that Eznec could not recognize the radials, or Eznec could not handle slanted and close together radials due to limitations. So, I'll ask again if you see my Vector/Sigma models showing maximum gain and angle that is very high in the 40* degree range? Could it be the other guy is wrong?

I will model your idea with radials slanged down at 45* degrees and see what Eznec predicts there. I have already done some modeling on a 3/4 wave radiator with horizontal radials angled up at several angles, as you might remember when you straightened me out before. Thanks for that lesson.

I did not use a hoop in those case, and that was in order to make the adjustments easier to model. I'm also not sure if I adjusted the radials to resonance as I went, but I'll check that if I use them to demonstrate your idea for slanting the radials down.

I'll expect to see slanting the radials down on a 3/4 wave radiator react similar to what happens with a 1/4 wave, but I'm not sure about the effects on gain and angle, if any. We'll see.

 

[Marconi]

Marconi, that model demonstrates the limitations with widening the angle very well. Once you begin exposing more of the first 1/4 wave on the vertical radiator, gain on the horizon goes down while gain in the 40 degree range goes up. That also happens ten fold once you sweep the radials out at 90 degrees or down on a 45.

It should also be pointed out a lot of this work is difficult and easily led astray. It's a labor of love to try and find any way to improve antennas and I'm by no means perfect. Case in point was following through with Avanti's suggestion in the patent that a wider angle would produce improved gain. You saw I built the antenna and even had it tuned to the point it led me to believe there were improvements as I once reported.

In the long run, the idea failed and the discrepancy in the field tests were traced back to deficiencies in the receiver being used to peak the gain. While gain in transmit is reciprocal to gain in RX on nearly all antennas, troubles can easily arise when you discover the input impedance on nearly every HF receiver is far from 50 ohms. That makes a huge difference when tuning for gain in what you assumed was a 50 ohm match. It took a network analyzer and some receiver work to correct that issue.

Well like I said in a previous post to you, I have already done some work with a 3/4 wave radiator with horizontal radials. I was hoping there was some difference to be noted as the radials went down, but knowing this is helpful in keeping me from looking for a response that is not there.

Concerning the match for the Sigma/Vector. It is too bad that I can't model the matching device. I have looked high an low for examples on the Internet and in books. There is some talk on the subject, but practical applications of matching CB models are rarer than hen's teeth.

 

[Shockwave]

Yep, words can be confusing and misleading sometimes, even my own. Arguing is OK as long as it is done with respect and consideration for another point of view, but I have questions to ask and statements to make that seldom come up in discussions, and when it does, it tends to inflame some. I don't deliberately intend to be mean in asking, but I know it appears that way sometimes...as I get excited,others tend to get excited in being questioned.



I'll be looking for this beam tilt too, so let me ask, do you mean a tilt below the horizon, or are you describing something else up much higher in the pattern?

I'm still waiting for someone to post some evidence in all this history of a upside down ground planes. I'm sure a few are out there looking this up as we speak.



Well that's good to know. All I've heard up to now is that some RF expert guys commented that Eznec could not recognize the radials, or Eznec could not handle slanted and close together radials due to limitations. So, I'll ask again if you see my Vector/Sigma models showing maximum gain and angle that is very high in the 40* degree range? Could it be the other guy is wrong?

I will model your idea with radials slanged down at 45* degrees and see what Eznec predicts there. I have already done some modeling on a 3/4 wave radiator with horizontal radials angled up at several angles, as you might remember when you straightened me out before. Thanks for that lesson.

I did not use a hoop in those case, and that was in order to make the adjustments easier to model. I'm also not sure if I adjusted the radials to resonance as I went, but I'll check that if I use them to demonstrate your idea for slanting the radials down.

I'll expect to see slanting the radials down on a 3/4 wave radiator react similar to what happens with a 1/4 wave, but I'm not sure about the effects on gain and angle, if any. We'll see.

The issue I see with EZNEC is not that it doesn't recognize the radials. It's that it only appears to see them carrying transmission mode currents and that's only half the job. It is the half that reduces the high angle lobe so that is why you don't see this characteristic in your current model. The second half of the job is antenna mode currents on the cone. This is where gain above the half wave comes into play.

It is the elimination of the radiation on the lower 1/4 wave vertical that reduces the 40 degree lobe. Since you can see these results in EZNEC, we know the program is recognizing transmission mode currents taking place as we "shield" over the vertical radiator. What takes a little more digging to uncover is the fact EZNEZ does not recognize radiation from the cone and mistakes the antenna as a 180 degree radiator.

You're probably curious as to how I'm sure EZNEC is wrong here and it's easier to explain then the work I had to do to prove it to myself. If you use EZNEC to design a collinear version of this antenna, it reports peak gain using a 180 degree (or half wave) phasing section. This is correct for a half wave radiator but fails miserably in the field because the phase angles are off by 90 degrees with this 3/4 wave. The same design shows peak gain in the field using a 90 degree phase delay, not the 180 degrees EZNEC reports.

That can only be true if a full 270 degrees (3/4 wave) of radiation had taken place prior to the 90 degree phasing section. You'll have to run the field tests yourself or just take my word on it that EZNEC is missing something on this antenna. That something appears to be the first 1/4 wave (or 90 degrees) of radiation taking place on the outside of the cone.

PS: The affects of slanting the radials down on a 3/4 wave ground plane are dramatic. It doesn't just shift impedance like on the 1/4 wave. It has a huge negative impact on the distribution of energy contained between the primary and secondary lobes. It is one of the few cases I'm aware of that significantly alters the main TOA other then height above ground.

 

[bob85]

shockwave,
are you saying a 1/4wave/90 degree stub which gives 180 degree phase shift does not work best with the sigma style antennas ?

 

[Shockwave]

shockwave,
are you saying a 1/4wave/90 degree stub which gives 180 degree phase shift does not work best with the sigma style antennas ?

Bob, you got me a little confused here. Wouldn't a 1/4 wave 90 degree delay line cause a 90 degree phase shift from the input to the output of that line? I'm failing to see how a 1/4 wave line could cause a 180 degree phase shift?

 

[bob85]

it depends where you look or maybe its just how im reading it,
cebik in his "some j-poles i have known" uses a 18.5" x 2" phasing section on 2mtrs for 90 degree shift between 2 x 1/2wave j-pole sections,
other sources say a 1/4wave long shorted stub shifts 180 degrees.

 

[Shockwave]

it depends where you look or maybe its just how im reading it,
cebik in his "some j-poles i have known" uses a 18.5" x 2" phasing section on 2mtrs for 90 degree shift between 2 x 1/2wave j-pole sections,
other sources say a 1/4wave long shorted stub shifts 180 degrees.

I think the difference here is due to the fact a 1/4 wavelength shorted phasing stub consists of two 1/4 wavelength conductors. When you short the end, the RF travels 1/4 wave down to the short and comes back on the other conductor after another 1/4 wavelength of travel. The end result is a 180 degree phase shift.

 

[Marconi]

Bob and SW, while you two argue high angle lobes, phase, and stub respondes, I'll ask a question, and make some comments.

Do you both figure there is somehow constructive collinear type phasing going on in the Sigma4 at the top of radials cone that produces the good results we see in the Vector/Sigma design? Is this what you both are trying desperately to prove?

For me this idea is based solely on a few undocumented words from a dead man, and can't be explained further from his point of view. What if this affect we see going on with the Sigma design is just a simple response associated with raising the radials, as apposed to something magic or mystical going on.

I think, I see, in my modeling that phasing two elements that are not electrically equal, tends not to show successful collinear type results. I'm not saying it can't be done, I'm just saying in my limited modeling experience...I don't see it. I see the model that Sirio presented, but I can't say for sure I understand fully what I see. It does look to me that the bottom cone is producing rf in phase that is contributing with the top, but it does not explain why or how it does that.

I also think what I see by pushing the radials up on a radiator .625 wave to .75 wave is the configuration itself is pushing down on the typical high angle lobe noted for all 1/8 and 1/4 wave radiators. IMO, this setup very simply allows the 1/2 wave radiator to be raised up higher than the .625 wave radiator as compared. So, therefore I believe this is the reason the Sigma design shows a modest increase in gain at a lower angle to the horizon when compared, and there is nothing special really going on. If you check out some of the models I posted over time I think you will see this modest difference indicated as well, and that is not just words.

I think SW is suggesting to Homer that raising the radials on a .625 wave will not produce similar results to the .75 wave, because there is not enough current flowing in the bottom 1/8 wave portion of a .625 wave radiator. I don't claim to understand much of SW words, but my models do not support this notion. I see the same pushing down of the higher angle lobes with the .625 wave...as I see with the .75 wave radiator.

I think you guys are trying to justify that the bottom of the Sigma is contributing constructively with the top of the Sigma via a phasing idea that does not exist, or at the very least is arguable. IMO, the idea of raised radials simply shows us that raises radials push the physical top 1/2 wave radiator up higher...than the top 1/2 wave for the .625 radiator. I would venture a wild guess here, that if you raised a 5/8 model up equal to the current node of the Sigma4, the results on of near the horizon would be similar or exactly the same, and that might also include the lower 1* in angle as well, seeing as height has such an affect on TOA.

I think I can demonstrate this idea with models Homer, if you want to see something besides just words. This said, I still remain open for someone to produce some real evidence in understandable English to the contrary...other that just words.


I will email Homer the results of these two models along with a brief explanation as I understand the work, because I think he is asking for such information. We will see if it makes and sense to him and if it does, then I'll post the project. Just let me know Homer. I will wait for your request or your denial.

In my opinion, regarding the Sigma4, I don't think it matters enough whether I'm right or if Bob and Shockwave are right, the Sigma designed antenna proves, by performance, that the act of raising the radials up works, solves the problems typically associated with radiators that are 3/4 wavelength, lowers the angle of maximum radiation by 1* degree compared to other designs at some heights, and works very well mounted low to the Earth...if mounted well into the open.

 

[HomerBB]

Marconi, the only question that comes to mind at the moment (at least until I see your email), is whether the point .625 and .75 that you refer to in the above post is the same as that to which SW referred. Are you both talking about these length in the overall lengths of the antennas, or from the cone ring upward.
When I built and mounted the Sigma antennas, whether 5/8, 3/4, or 7/8, I measured from the bottom of the antenna to the tip top fr those lengths.
Are you fellows on the same page here?