An antenna experiment that Freecell once told me about.

[Marconi]

Shockwave I set my Vector model upside down at 36' feet (USD) and it shows:

1.81 @ 13* usd over real Earth so this is not much help even on a mountain.
2.97 @ -6* usd in free space so there is some tilt down noted
4.83 @ 8* right side up over real Earth

 

[hookedon6]

...
My point was that except for the height of the current nodes being different due to the antenna design, these antennas probably all produce about the same gain and angle...when the height advantage/disadvantage is removed from the test.

huh???????????? BASIC antenna theory,............radiation angle is a function of height over ground.


if your modeling program doesn't show a difference between "normal" and "inverted" configurations, then the software is deficient..

the TOA is the MIN angle, there is also a MAX angle too. what we are concerned with is the vector area SHIFT contained BEWEEN the 2 when an antenna is inverted.

by changing the relative TX antenna height , the "cone" of radiated RF is directed at, below, or above the RX antenna, this is true with both inverted and normal mounted vertical antennas.

 

[hookedon6]

... The counterpoise tends to push the signal slightly upwards. If you invert the antenna, the opposite affect is true, the signal is of a slight downward tilt. What works best depends on your desired coverage area and the location the antenna is used in.

This also suggests that FreeCell's claims of improved downward coverage from his mountaintop location while experiencing simultaneous improved skywave coverage is not likely... You can't claim you've improved gain below the horizon and in the good skywave range about 15 degrees above the horizon at the same time..

'zactly correct, what is happening, by inverting a vert GP, is the radials, when inverted, become an artificial ground above the antenna, with the MUCH larger REAL (earth) ground below the antenna.

which do you think has the most effect?,... a small 1/4 wave artificial ground or the planet earth?

 

[HomerBB]

And just for grins.
That radiation angle isn't determined by the symmetry of the antenna so much as by it's height above ground. There's no 'ground in free space so different radiation angle naturally. The 'shape' of an antenna can have an affect on radiation angles but not as much as 'dirt' does. So, use that dirt!
- 'Doc

I have just been reading so far, but you just expressed my thoughts on it, Doc.

So far, Marconi's models are showing no improvement. It seems Monsieur E. Z. Nec hasn't been convinced, yet.

Perhaps this is because the software is reading the new bottom of the antenna at 36' when inverted rather than the feedpoint at the top? The current node may be shifting due to the influence of the earth?

 

[Marconi]

I have just been reading so far, but you just expressed my thoughts on it, Doc.

So far, Marconi's models are showing no improvement. It seems Monsieur E. Z. Nec hasn't been convinced, yet.

Perhaps this is because the software is reading the new bottom of the antenna at 36' when inverted rather than the feedpoint at the top? The current node may be shifting due to the influence of the earth?

Homer, your suggestion here that I was looking for improvement is not what I was trying to demonstrate. It is obvious that I see the SD'r model and the results differently than you guys.

Keep in mind that I described my SD'r at 36' feet high, because that is the height of the model I used for this project. I wanted to see if what FC told me could be true, that his SD'r positioned upside down would radiate the maximum signal down below the horizon...as he noted from the side of his mountain location. He said it help him and I believed he probably saw what he saw, but I didn't agree with the idea. This is the reason I modeled the idea to see what Eznec might predict.

If you will consider for a minute where the feed point is on a SD'r, you will see that the antenna is balanced and center fed, and that flipping it over at the feed point changes nothing relative to the current node. Again the feed point is at 36' feet, and that is unlike what would happen if I flipped over a 5/8 or an end fed 1/2 wave antenna and set them at the same feed point height.

Because the SD'r is balanced and center fed is why we see these models showing no change in height, gain, angle, or pattern when we flip it upside down. I'll admit I did not know the details for why, until I did this model project, but I took exception to FC's idea back then none-the-less. That was because in my thiniking that was not what I would have expected, and that was base on what I had in my minds eye for a 1/2 wave dipole pattern looking like a circle or 1/2 a circle.

You guys thinking here seems to be stuck on considering a 5/8 wave only, or in your case Homer, your end fed 1/2 wave. In Shockwave's case he is thinking and talking about his Vector being flipped over. Each of you is forgetting that FC and I were talking about a center fed Starduster. These other antennas did no come up in my discussion with FC.

Again, I only did my 5/8 wave model after SW mentioned his Vector. I did a 5/8 wave model so I could see if there was any difference. I saw a noticeable difference so I posted same showing the difference between the SD'r and the unbalanced 5/8 wave antenna...you're all focusing on.

You guys are correct, there will be differences regarding these other unbalanced antenna designs. The patterns, gain, and angle would change on flipping, just as my 5/8 wave model shows.

 

[HomerBB]

I guess I don't know how to read the information on the modeling .pdf's, but I saw no change on the StarDusters to speak of, and a worsening of TOA on the .625.
So either way you approach the idea, the changes are BAD, or non-existent.

 

[Marconi]

I guess I don't know how to read the information on the modeling .pdf's, but I saw no change on the StarDusters to speak of, and a worsening of TOA on the .625.
So either way you approach the idea, the changes are BAD, or non-existent.

No Homer, I think you understand what you're looking at alright, but instead of considering what happens in this case with FC's SD'r, you have in mind what would happen with your EFHW instead, at least that is the way you seemed to described the problem I had.

My upside down 5/8 wave model was done to show the bad results I saw, and the SD'r model was to suggest that FC's idea was dubious at best. Before I made the 5/8 wave upside down, I had no idea what that one would do. I made the claim that the SD'r pattern did not change when upside down due to its symmetrical design, and I think that probably started all the disagreement...where there probably is none.

Answer this question if you can.

Shockwave suggested to us that he knew about turning antennas upside down, and others said much the same, saying it is a popular idea in certain situations. SW also suggested that turning antennas upside down could possibly produce certain benefits for his Vector styled FM antenna, kind of like what FC was suggesting for his SD'r. SW even went further with this positive result idea, and he claimed he was considering to recommend upside down mounting to certain of his customers.

Shockwave, could you clarify this a bit or prove your point that there are benefits to be had with your antenna upside down?

BTW, while I'm at it, I have another question for you. Whatever happened to your wide angle Vector idea that Bob posted about some time back. We saw pictures of it, but later when it came time for some results, the idea just died out and you and Bob, who were so hot on the idea, just stopped talking about it. What happened to that idea?

Homer, in light of this discussion and my presenting my story and my models, you have come to some conclusions, where I read your remarks to 'Doc, as being somewhat off point, and misleading as to what I was trying to demonstrate. Dirt is important to antennas no doubt, but that was not the topic either.

However, I'm not real sure what your point is exactly, but ask yourself why on Earth would Shockwave consider to recommend installing his Vector styled FM antenna upside down, considering what you are now saying in your remarks above, suggesting the results are either no change with the SD'r, or bad changes with the .625. Does that suggest that the Vector antenna will be an exception to our getting bad results when we turn it upside down?

We don't know for sure if turning antennas upside down has any benefits to offer at all. Thus far this idea is only Internet words, and based on my modeling examples, I doubt we will find any conclusive evidence to the contrary, but I am encouraging anyone who can to produce such contrary evidence to come forward.

I am curious, I can acknowledge my own errors, and I am forgiving to a point.

 

[Shockwave]

The radiation patterns of the 5/8 wave deserve a closer look because they do support the idea that inverting the antenna can reduce skywave activity. Notice what is happening to the gain in the 15 to 20 degree range. When the antenna is inverted we see a null there. Right side up and we have a secondary lobe peaking out right in that range. Your specific results will obviously vary with height.

Marconi, with respect to the wide angle Vector, there is a point of diminishing return with this idea that was not pointed out in the old Avanti patent. They mention that wider angles can increase gain but avoid the fact the physical length of the cone section must line up with the first electrical 1/4 wavelength of the main radiator. This is important to confine the undesired radiation taking place inside the cone. Since the electrical length of the cone and loop combined must also equal 1/4 wavelength, there is only one ideal dimension that meets all of the requirements.

As mentioned earlier, my consideration of inverting my antenna was for specific installations where two antennas must be stacked and phased together. At .82 wavelength long, this makes the standard vertical stacking distance difficult to achieve without negative interaction. The very high RF voltage tip of the bottom antenna is too close to the grounded side mount bracket for the antenna above it. That creates a prime location for a Corona arc to take place.

If I invert the bottom antenna, that problem goes away. It may also create a situation where the nulls in one antennas pattern can be more easily filled in by the second antenna. It does appear that none of this will provide downward beam tilt over real earth however, with the stacked pair this option is easily added with a small phase delay inserted with one antenna.

 

[HomerBB]

you have in mind what would happen with your EFHW instead, at least that is the way you seemed to described the problem I had.

Actually, Marconi, of the antennas I've used only the Astroplane came to mind as one I'd bother attempting such a thing. This is due to the limited ability i have to mount an antenna upside down. Anything else would have to hang upside down from its current feedpoint height and result in the antenna being lower than it is removing any real comparative results.

The radiation patterns of the 5/8 wave deserve a closer look because they do support the idea that inverting the antenna can reduce skywave activity. Notice what is happening to the gain in the 15 to 20 degree range. When the antenna is inverted we see a null there. Right side up and we have a secondary lobe peaking out right in that range. Your specific results will obviously vary with height.

Marconi, with respect to the wide angle Vector, there is a point of diminishing return with this idea that was not pointed out in the old Avanti patent. They mention that wider angles can increase gain but avoid the fact the physical length of the cone section must line up with the first electrical 1/4 wavelength of the main radiator. This is important to confine the undesired radiation taking place inside the cone. Since the electrical length of the cone and loop combined must also equal 1/4 wavelength, there is only one ideal dimension that meets all of the requirements.

As mentioned earlier, my consideration of inverting my antenna was for specific installations where two antennas must be stacked and phased together. At .82 wavelength long, this makes the standard vertical stacking distance difficult to achieve without negative interaction. The very high RF voltage tip of the bottom antenna is too close to the grounded side mount bracket for the antenna above it. That creates a prime location for a Corona arc to take place.

If I invert the bottom antenna, that problem goes away. It may also create a situation where the nulls in one antennas pattern can be more easily filled in by the second antenna. It does appear that none of this will provide downward beam tilt over real earth however, with the stacked pair this option is easily added with a small phase delay inserted with one antenna.

Adding this post to the thread gives a fuller picture of expectations for this kind of inverted maneuver. Thanks.

I would be very, very interested in this piece - ". . . fact the physical length of the cone section must line up with the first electrical 1/4 wavelength of the main radiator. This is important to confine the undesired radiation taking place inside the cone. Since the electrical length of the cone and loop combined must also equal 1/4 wavelength, there is only one ideal dimension that meets all of the requirements."

Is there a number/dimension that is knowable, or is one stuck having to guess he got it right? Real life tests are so subjective,

 

[Marconi]

The radiation patterns of the 5/8 wave deserve a closer look because they do support the idea that inverting the antenna can reduce skywave activity. Notice what is happening to the gain in the 15 to 20 degree range. When the antenna is inverted we see a null there. Right side up and we have a secondary lobe peaking out right in that range. Your specific results will obviously vary with height.

Marconi, with respect to the wide angle Vector, there is a point of diminishing return with this idea that was not pointed out in the old Avanti patent. They mention that wider angles can increase gain but avoid the fact the physical length of the cone section must line up with the first electrical 1/4 wavelength of the main radiator. This is important to confine the undesired radiation taking place inside the cone. Since the electrical length of the cone and loop combined must also equal 1/4 wavelength, there is only one ideal dimension that meets all of the requirements.

As mentioned earlier, my consideration of inverting my antenna was for specific installations where two antennas must be stacked and phased together. At .82 wavelength long, this makes the standard vertical stacking distance difficult to achieve without negative interaction. The very high RF voltage tip of the bottom antenna is too close to the grounded side mount bracket for the antenna above it. That creates a prime location for a Corona arc to take place.

If I invert the bottom antenna, that problem goes away. It may also create a situation where the nulls in one antennas pattern can be more easily filled in by the second antenna. It does appear that none of this will provide downward beam tilt over real earth however, with the stacked pair this option is easily added with a small phase delay inserted with one antenna.

Well this 5/8 wave model may be all wrong. If the modeling experts were talking, they would probably confirm that. However, since nobody is talking up, even Henry, why don't we take this model, for arguments sake, as correct or at the very least close enough. We can always come back and say it was dead wrong, and I'll back you up if true.

The way I read your original post, where you referred to you considering to recommend inverting your antenna mount upside down to certain of your customers that used single antennas, is a bit different from what you said above.

SW, I can make judgments about mistakes, but I tend to get real confused when the words I read don't mean what they say. Here is what you originally said regarding your recommending this upside down install to your customers.

The Sigma design actually has a free space peak gain between 1 and 2 degrees above horizontal 0 degrees. 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. We may also begin recommending stations using a single antenna at extreme elevations, side mount the antenna upside-down.

I assume you have not modeled any of these ideas including the wide angled Vector, because in my opinion if you had, you would surely be discouraged in proceeding with such ideas.

Here is what I get using my New Vector model right side up and upside down.

If you can tell me why I don't see the bad results with this model that you earlier claimed you had a dozen antenna modelers work on, all saying in the end the best maximum gain and angle would be up in the 40* degree range, and that was because Eznec could not recognize the radial design for the Vector?

View attachment Shockwave's upside down Vector idea..pdf

I figure if you showed these results to a customer you would have a hard time convincing him to turn his antenna upside down...under any circumstances.

 

[Marconi]

Actually, Marconi, of the antennas I've used only the Astroplane came to mind as one I'd bother attempting such a thing. This is due to the limited ability i have to mount an antenna upside down. Anything else would have to hang upside down from its current feedpoint height and result in the antenna being lower than it is removing any real comparative results.

The A/P is also a balance type antenna. I presume it too is center fed, so it may work as my model of the SD works, just spin it around on the feed point to make it up side down and I would bet we would see a very similar pattern compared to it being upright. Mounting upside down would be a problem that needs consideration for any antenna.

Do you see now, that only a center fed antenna will go upside down without changing the pattern it produces very much at all? That is all I've been say here.

Adding this post to the thread gives a fuller picture of expectations for this kind of inverted maneuver. Thanks.

I would be very, very interested in this piece - ". . . fact the physical length of the cone section must line up with the first electrical 1/4 wavelength of the main radiator. This is important to confine the undesired radiation taking place inside the cone. Since the electrical length of the cone and loop combined must also equal 1/4 wavelength, there is only one ideal dimension that meets all of the requirements."

Is there a number/dimension that is knowable, or is one stuck having to guess he got it right? Real life tests are so subjective,

This is a good modeling idea to consider Homer, if we truly understand the implications noted in the limitations on this issue. In my application I attempted to follow the suggestion noted. However, due to the radials at an angle with the radiator you will see an error creep in the implementation. I also did as noted in this area of the instructions and tested the idea, and I found little to no noticeable difference as long as I stayed close to the rule.

Again all this hoopla about this limitation or that, looks to be a portion of crying Wolf. The particular factor is true, I have experienced the consequences, but it is strictly a matter of degree and magnitude when we think about these type of errors and what limitations mean. Just reading some words won't tell the story.

Being curious, this is why I ofter ask the question, "...how much difference are you talking about?"

In a post above I just asked SW the question to tell me why my models don't show what his 12 antenna design experts predicted would happen using Eznec, where they all 12 claimed that Eznec could not recognize the radials in such a design, and the models would show a max gain and angle at or about 40* degrees, as noted to be indicative of all 3/4 wave radiators.

If we read the full section on this limitation for close wires, there is some exception to the rule that no body seems to want to talk about. I have tested this idea on several of my models and I find the rule is well based in truth and will actually stop you from proceeding with an Eznec scan if you exceed the limitation. However, I found a basic way to mitigate the problem, and it follows from common sense thinking, experience, and testing. If one only thinks about the issue and considers what happens when we try and connect two wires together the idea is quite clear.

This is all I'm going to say on the subject, because I do not get help from others, and I am provoked to respond the same with modeling.

Homer I did talk to you about this and I showed you the words, so I hope you will honor this confidence, but if you choose not, then that will be alright, I'll understand. Plus this idea is so easy to figure out anyway, if you understand Eznec just a little. Personally I don't have much fear of the idea getting out this way, because most are so locked into their own thinking, they cannot see the forest for the trees, so-it-is-said.

 

[TonyV225]

I have heard alot of crazy things as far as antenna mounting and I heard also about the working with elavation problems. Sometimes it sounds stupid idiotic and crazy but Ive myself seen thinks work that absolutely should not have but I would al;ways laugh and say "welcome to the wonderful world of electronics and radio"

Ive personally messed around with an Antron 99 lying on the roof before mounting and when taking a break messing with it and making a contact!! Ive seen and done other thimgs that were just crazy nuts that worked with no explanation rather against al;l laws of physics or electrical theory or not. Its just weird how things work sometimes and we can scratch our heads until were bald and most likely wont get an answer or figure it out.

I will say one thing and reguardless of peoples issue with Freecell that man is a extremely intelligent man when it comes to electronics and radio Ive talked with him several times on the phone and its to bad his busniness ethics were not so hot. :sad:

 

[HomerBB]

Tony,
I'm with you on the point of things happening when they were not supposed to. That's the main reason I started a thread (not this one) that was supposed to focus mainly on what folks experienced. I hoped folks would be willing to speak up about some of those exceptions.

Marconi,
I'm glad you posted your Vector model. I haven't mentioned it, nor any of our discussion on the subject, however, I think what is to be learned from the models is valuable.

 

[Shockwave]

Adding this post to the thread gives a fuller picture of expectations for this kind of inverted maneuver. Thanks.

I would be very, very interested in this piece - ". . . fact the physical length of the cone section must line up with the first electrical 1/4 wavelength of the main radiator. This is important to confine the undesired radiation taking place inside the cone. Since the electrical length of the cone and loop combined must also equal 1/4 wavelength, there is only one ideal dimension that meets all of the requirements."

Is there a number/dimension that is knowable, or is one stuck having to guess he got it right? Real life tests are so subjective,

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.

 

[Shockwave]

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.

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 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.