Fat EFHW

[hotrod]

In the modeling I put the feedpoint as close to the bottom of the vertical element as possible. I suppose I can move the radials around a bit, and do like the a99/imax antennas do and put them further away. One thing that comes into play is these antennas all have a matching system, which should, in and of itself, tune the radials as well as the antenna, perhaps making the absolute length of the radials less critical on an antenna with such low radial currents to begin with?


The DB

DB i will say you are smarter than me about antennas. but my opinion was formed
based on real world results. maybe im just old school . but you remember putting up
a antenna on a xxfoot tower/pipe then compared another antenna on same tower/mast
coax at exact same spot.those are my tests which one works the best at a given height
at a distance say 40 miles, so no skip talking , no conditions were just right. the antenna
either performed or it didnt. at different locations ive tested antennas with some
minor changes , so i will say location does play a part .for 20 years or more ive tested
antennas similar to this.

 

[The Bruce]

Fat? Maybe a little chubby, but not fat...
- 'Doc

Size? It all about how you use it, at least that's what my wife tells me more and more these days.

(not exactly sure why that is)

 

[Marconi]

In the modeling I put the feedpoint as close to the bottom of the vertical element as possible. I suppose I can move the radials around a bit, and do like the a99/imax antennas do and put them further away. One thing that comes into play is these antennas all have a matching system, which should, in and of itself, tune the radials as well as the antenna, perhaps making the absolute length of the radials less critical on an antenna with such low radial currents to begin with?

DB, you posted your EFHW model with and without horizontal radials. Later I made a model to see if I could duplicate what you did. I posted my Eznec results and our results were pretty much identical.

In this thread Homer shows us his new version of his Fat EFHW without radials. I think he is also telling us that a previous EFHW he had, with radials, showed to be his best performer.

Homer did your best performer by chance have slanted radials?


DB, I would be interested to see your EFHW model with slanted down radials and a 12" x 1" tube mount below the radial connection. This might provide for a more accurate A99 model like Homer is suggesting. This will also allow for the radials to be easily placed at the top or bottom of this new 12" x 1" base mount, and maybe we'll see a difference like Homer notes may be possible.

I think Homer is suggesting a relocation of the radials might show some difference, a difference that our previous models with horizontal radials vs. no radials did not show.

 

[The DB]

DB, I would be interested to see your EFHW model with slanted down radials and a 12" x 1" tube mount below the radial connection. This might provide for a more accurate A99 model like Homer is suggesting. This will also allow for the radials to be easily placed at the top or bottom of this new 12" x 1" base mount, and maybe we'll see a difference like Homer notes may be possible.

I think I did what you wanted.

The first thing I did was add in angled radials, then added your short tube under the antenna to all of the models in question.

The angled radials presented a better overall gain than any other design, comparison plots with matching networks...

Adding the short tube you mentioned helped gain in all models, but only to an insignificant degree. It did help the no radials model noticeably more then the others, but still only an insignificant amount overall, but only after matching was added in.

Looking at the feedpoint impedances before and after, the short tube had far more of an effect on the no radials model than the other two. In plots that did not factor in matching the added tube added the same amount of gain (0.02 dB) as the other two models. However the tube affected the feedpoint impedance of the no radials model noticeably more than the other two, benefiting it more than the other models when it came to matching efficiency. I think the radials in the other models plotted dominate the antenna on that side of the feedpoint, as such the smaller tube has noticeably less of an effect to their feedpoint impedances...

As the A99 was talked about by myself and others in this thread I took my modeling a step further, I made a comparison model between full length angled radials, and the shortened angled radials that is used for the a99.

The ar plot is the angled radials plot from above, the ar2 plot is the shortened angled radials plot. The shortened angled radials plot has slightly more gain (0.04 dB), but still an insignificant amount over no radials. This is actually due to matching as well, as the shortened angled radials presents a better match.



The DB

 

[Marconi]

Thanks DB.

DB, I know it is more work, but the only way I can get a sense for what you might be doing with a model or understand what a pattern you post might really mean sometimes, is when when you also post the antenna view.
That might save me asking you a lot of questions.

Thanks for doing all the extra work. I didn't mean to try and instruct you in modeling, but when I read Homer's post I think I got the idea he was questioning our models, partly because the models did not look completely like an A99. I was agreeing too and felt a little change in the model would possibly might make a difference...just like he suggested. That said however, I still see this difference as very small DB, just like you do.

I think you nailed the idea here, that I was thinking about, except I did not consider matching or the effects of matching.

I just posted a model of my dipole and changed the feed point to an EF, added horizontal radials to compare to no radials, and we saw no change in the patterns and a little small changes in the other performance factors. However, our models were similar.

Does the use of the matching feature change the SWR, pattern, gain, and/or angle...compared to a similar model with no matching?

When you match a model does it make a difference in the SWR results that you see in the model's SWR details?

If so, after the match is fixed on the A99, are you able to run a successful SWR and/or bandwidth curve for the model like Eznec allows...when you have a good match and the SWR is fairly low on the scale?

When I add a load or a transmission line I see a small box or a circle pop up on the antenna view with Eznec. Does the addition of a matcher show up in the antenna view with your software with a symbol or icon so you know the model is matched and the effects are present in the model?

 

[The DB]

except I did not consider matching or the effects of matching.[/I][/B]

Two different people can look at the same thing and see two different things. Other people's experience are always useful, especially to a modeling novice like myself.

I just posted a model of my dipole and changed the feed point to an EF, added horizontal radials to compare to no radials, and we saw no change in the patterns and a little small changes in the other performance factors. However, our models were similar.

OK so we are either both on the right track, or both wrong... I like to think that we are both on the right track, especially when we are using different bands for our models, I am actually using a frequency that is considered in the 10 meters band as you might note by the frequency in the upper right corner of some of my posted images...

Does the use of the matching feature change the SWR, pattern, gain, and/or angle...compared to a similar model with no matching?

Adding the matching network to the model seems to do several things.

1) The SWR data is corrected for the model
2) The matching network's loss characteristics are factored into efficiency
3) Phases in the model are corrected for the presence of the matching network

I don't think the SWR correction really has any effect anywhere except the SWR data.

However, the loss characteristics being adjusted seems to lower the overall gain, this would make sense.

I mentioned a phase correction that I noticed, I'll post some pics here, first the unmatched antenna...

Once I add the matching network the same spot of the antenna looks like this...

In this case the change in the phase of the various parts of the antenna had minimal if any effects on the pattern. I think that this was mainly due to the fact that there are minimal currents on the effected parts of the antenna. Because of the fact that there is a change I cannot rule out the possibility of the matching network on other antennas causing a change of some sort in the radiation pattern, but I don't have enough experience to know for sure...

When you match a model does it make a difference in the SWR results that you see in the model's SWR details?

Answered, see above.

If so, after the match is fixed on the A99, are you able to run a successful SWR and/or bandwidth curve for the model like Eznec allows...when you have a good match and the SWR is fairly low on the scale?

I can run a scan over a set of frequencies and display things like SWR, gain, and other things as well for that frequency range. I can do this irregardless of the matching network.

When I add a load or a transmission line I see a small box or a circle pop up on the antenna view with Eznec. Does the addition of a matcher show up in the antenna view with your software with a symbol or icon so you know the model is matched and the effects are present in the model?

The only thing that tells me that a matching network is present is the info box on the main data screen has a line with the text "MATCHING NETWORK PRESENT", among other bits of information. I can tell you that if I use the stub matching option, it will show the stub itself in another color on the display that shows the antenna layout, so the phase examples above would include the stub wires in another color...


The DB

 

[Marconi]

OK so we are either both on the right track, or both wrong... I like to think that we are both on the right track, especially when we are using different bands for our models, I am actually using a frequency that is considered in the 10 meters band as you might note by the frequency in the upper right corner of some of my posted images...

The DB

DB, I could be wrong, but based on what I'm seeing with my new models that have the A99 base mount added to the model...I don't think we are on the right track as you suggest.

I think Homer may be making a valid point in his concerns with the models we've posted thus far. I don't have a solution either, but I hope to figure something out soon, and post some of my thoughts as I see and analyze my models.

I've have made 5 new models using my original model titled Dipole .50 wave 18'. I changed the title for each new one to "A99....etc." Then in order to make the models look more like the specs on the A99, I added 12" x 1" tube as the base mount. I changed my wire diameters from .625" tubing to .0625" wire for the thin wire inside an A99. I then added horizontal and slanted radials at the top of the mount, and then did the same at the bottom of the mount, so I have 5 new models.

I think I see very little difference in the gain results between these models just like earlier, but the match and the current magnitude values are way different among these several models. So, I'm questioning my work here, and asking if I've exceeded Eznec's limitations somehow.

If I can resolve this concern I will follow up with you DB. Again I got similar gain and angle figures in the models, but after all the changes I made the match, SWR, and the magnitude of phase change looks to have changed remarkably, and I was not expecting that.

I've also noticed that the phase your models show compared to mine are similar in places and different in others, so I started looking at the currents. I see that 4nec2 generates the phase magnitude by color variations, but does it also show tabular values?

To me currents are very important in modeling even though I don't have a good handle on how and what they all mean, and nobody talks about this aspect in modeling that I know of.

I'll go ahead and post my model soon, and maybe you will see something I missed and I will try to mark the data up to give you my ideas for what it means.

Considering the changes I've made, I'll be surprised if our models compare so well as they did earlier.

 

[The DB]

I see that 4nec2 generates the phase magnitude by color variations, but does it also show tabular values?

Not directly that I have seen. The tabular data is available in the .out file from the nec2 engine, so I can see that data if I wish but I have to go find it. I use the color diagrams to represent current because I think that it is easier to read/understand. 4nec2 will show the same curved lines to represent current as eznec if I wish, I just don't like that view as much.

To me currents are very important in modeling even though I don't have a good handle on how and what they all mean, and nobody talks about this aspect in modeling that I know of.

Currents are key in modeling. The nec2 engine seems to use these currents in place of the fields generated by an actual antenna to determine the antennas radiation pattern. In most cases it is an effective shortcut, but there are times it has its limitations (example Vector 4000).

I'll go ahead and post my model soon, and maybe you will see something I missed and I will try to mark the data up to give you my ideas for what it means.

Considering the changes I've made, I'll be surprised if our models compare so well as they did earlier.

As long as the differences are where there are very low magnitude currents I don't see much of a change happening, but I suppose it is possible. I think the biggest change in gain on these models will be the gain correction for adding in a matching network and its additional losses...

Also notes on my models above, they are definitely not designed around the a99 antenna, and are not even designed at an 11 meters frequency. While that shouldn't matter, I am using a near perfect half wavelength for the frequency chosen, and that frequency was chosen to get me close to a perfect, if you will, 10 meters. The half wavelength is 5 meters long exactly, and the quarter wavelength radials are 2.5 meters long exactly. I did this for ease of antenna design as I prefer to use meters while using 4nec2.

I have added items seen on the a99, but the vertical length/width is *not* based on the a99 antenna and was not meant to be originally. It was meant to be an example of a half wavelength antenna that was as close to a half wavelength on the frequency in question as I could get. If you are using lengths based on the a99 design I would expect to see some differences in our models. I did add in some features of the a99 antenna by request and because I was curious as to the effect, but those are incidental, and while I noticed a few things with them, they are not part of what I was initially trying to show.

Just wanted to make sure that info was out there.


The DB

 

[jazzsinger]

Size? It all about how you use it, at least that's what my wife tells me more and more these days.

(not exactly sure why that is)

Maybe she bought a Sigma 4 lol

 

[Marconi]

Not directly that I have seen. The tabular data is available in the .out file from the nec2 engine, so I can see that data if I wish but I have to go find it. I use the color diagrams to represent current because I think that it is easier to read/understand. 4nec2 will show the same curved lines to represent current as eznec if I wish, I just don't like that view as much.

Currents are key in modeling. The nec2 engine seems to use these currents in place of the fields generated by an actual antenna to determine the antennas radiation pattern. In most cases it is an effective shortcut, but there are times it has its limitations (example Vector 4000).

As long as the differences are where there are very low magnitude currents I don't see much of a change happening, but I suppose it is possible. I think the biggest change in gain on these models will be the gain correction for adding in a matching network and its additional losses...

Also notes on my models above, they are definitely not designed around the a99 antenna, and are not even designed at an 11 meters frequency. While that shouldn't matter, I am using a near perfect half wavelength for the frequency chosen, and that frequency was chosen to get me close to a perfect, if you will, 10 meters. The half wavelength is 5 meters long exactly, and the quarter wavelength radials are 2.5 meters long exactly. I did this for ease of antenna design as I prefer to use meters while using 4nec2.

I have added items seen on the a99, but the vertical length/width is *not* based on the a99 antenna and was not meant to be originally. It was meant to be an example of a half wavelength antenna that was as close to a half wavelength on the frequency in question as I could get. If you are using lengths based on the a99 design I would expect to see some differences in our models. I did add in some features of the a99 antenna by request and because I was curious as to the effect, but those are incidental, and while I noticed a few things with them, they are not part of what I was initially trying to show.

Just wanted to make sure that info was out there.

The DB

DB, I did my new modified models based on my original (Dipole .50 wave 18') I posted...with and without radials.

I modified this model by making it look more like an A99. I'm not sure right now why I did this A99 thing however. This is what I was suggesting to you when I said I did not think we would see our revised models, with a 12" x 1" mount added to the base, compare similar anymore.

You note above that you took another approach trying to revise your models to better help address Homer's concerns about modeling. And I think matching and adding the base mount is the better approach. You added the mount, and the matching to your original models...which I can't do at this point.

Note: maybe you can give me some tips on this matching process later...so I can try and duplicate the feature using Eznec. I'll make a new thread to see if you can nurse me thru the process you use to add matching.

I too made multiple modifications to my models and my results now show notable differences compared to my original (Dipole......) models...with and without radials. So, at this point I can't tell what changed what. I'll do the mods over, and maybe I can tell what did what.

Now I question if the mods I made will help us understand better. Anyway, I'll post an image of my notes on the models that shows the results I got, so you can check-out the differences I see. I'm just not sure these results will be helpful at this point. I was really surprised when all I did was to make my model look more like the real A99, adding a 12' x 1" mount at the base, and changing the wire diameter for the wires from .625" to .0625" wires. I would post the models, but for now I'll just post my notes for the model results I got.

I hope you can read this, if not and you are interested in the details...you can increase the font at the top of the PDF file or you can print it out.

View attachment A99 with and without radials.pdf

Note: the captions for the data elements cover two lines on this narrow page.

 

[Marconi]

DB, take notice of the shift in the sign (+-) for the reactance between the horizontal radials with + reactance and those slanted down showing a - reactance?

Also notice the poor gain values for the radials attached to the bottom of the mount too.

 

[HomerBB]

Just a quick question with your comparison between half wavelength antennas, did you use the same matching network design and components just tuned to the various different half wave antenna layouts?


The DB

I wanted to give you a photo of the radials/antenna combo I was using when I finally rested from working on it.

This is the matching system in a smaller box as I am currently using it.

There were 12 x 48" radials. The vertical aluminum radiator descended right down to the top of the radials behind the box the matching system is in. The clamps holding the antenna to the mount/mast were attaching the metal antenna to a nonconducting fiberglass tube for 2' below the radials.

 

[Marconi]

Just a quick question with your comparison between half wavelength antennas, did you use the same matching network design and components just tuned to the various different half wave antenna layouts?

The DB

Homer, can you answer DB's question here...I'm interested too?

I wanted to give you a photo of the radials/antenna combo I was using when I finally rested from working on it.

This is the matching system in a smaller box as I am currently using it.

There were 12 x 48" radials. The vertical aluminum radiator descended right down to the top of the radials behind the box the matching system is in. The clamps holding the antenna to the mount/mast were attaching the metal antenna to a nonconducting fiberglass tube for 2' below the radials.

Aside from adding the radials and the new box for the matcher, is this the same radiator that you first posted?

If so, was the tune off much after adding the radials?

 

[HomerBB]

The answer to DB's question is yes.

The answer to Marconi's question is no.
However, the details of the changes with several MFJ-259b photo results as we, Marconi, and I, worked through the tests are available on my original EFHW thread linked in a previous post within this thread. Reading through it again may shed some light on any puzzles.

 

[Marconi]

The answer to DB's question is yes.

The answer to Marconi's question is no.
However, the details of the changes with several MFJ-259b photo results as we, Marconi, and I, worked through the tests are available on my original EFHW thread linked in a previous post within this thread. Reading through it again may shed some light on any puzzles.

Thanks for the answer to DB's question. I was thinking you told us you were using the same matcher, but I wasn't sure.

Homer, maybe you missed it, but I asked 2 questions and one was a follow-up.

Aside from adding the radials and the new box for the matcher, is this the same radiator that you first posted?

If so, was the tune off much after adding the radials?

I wasn't just being curious Homer, I had a reason for asking, but I didn't want to spoil the puzzle you mention. It all goes back to my ideas concerning the EFHW and radials.