Marconi,
The way i look at your model:
The SWR at 27,275, its equal to 2:1.
Higher in the band your model shows it is lower, but that will mean you will need to extend length.
That will influence other things like gain/fb as well.
Looking at your Model it is 1: 1.4 at 27.9 Mhz
but the gain there has dropped to 3,19 dBI. (azi plot)
(less than a standard 5/8 wave) any dipole will outperform the antenna.
Think I have said it before, but one can not do too often..
You have to bare in mind the program.
People question NEC if it is accurate, but it the operator which makes it accurate or not.
As soon as I “input” your data, I get a warning from Eznec…segmentation warning !
Its not there to ignore.
Besides that, I always say…be aware of the average gain figure which is around 0,95 …not that accurate.
You think you have a nice elevation pattern provided, but please do reconsider if it is accurate or not.
No…perhaps dont reconsider but better try a few different segmentations and you will find out the pattern will change.
While fixing the segmentations keep an eye on what the SWR does.
Indeed, the provided SWR by your initial model is a bit optimistic isnt it ?
the antenna is higher in the band resonant, it will probarbly go in the direction of 27,9 but more like 29 Mhz.
Because of the above reasons I haven’t looked further into the model.
From this initial point of view it looks like the simple groundplane or ½ wave vertical will be a better option.
The advice, if im allowed to provide..please take a closer look to the segmentations and the average gain figure.
With that said, you migth wanna look up what the NEC manual tells you about "bends" and keep that in mind as soon as you "publish" data.
I hope it was of use...if not pse do let me know where to be of assitance.
Kind regards,
H.
Henry, I have more to say here, but right off these models were done this way on purpose. Assualter and maybe Homer only have the Demo version, so I modeled this project with no more than 20 segments so they might be encouraged to and try using Eznec.
Since I have already posted the models earlier, it would be rather confusing now to change the segments all around, but I understand your point.
I try to be constructive in my discussions, and sometimes instructive, but I never wish to be destructive. I think you intend to do the same, but I had a time trying to understand what your point was in you first comment above.
I hope I got your second comment right however. I had to scratch my head a bit.
This is for those that didn't get what Henry was referring too. I took my
model with a mast and reset the frequency to 27.9 just for you Henry. Then I did an overlay comparing the difference as if I fixed the original dimensions Homer gave us to the 27.9 higher frequency. The problem with us having this discussion, here and now, will be the difficulty it will cause for these other guys understanding. Using Eznec to demonstrate an idea is already difficult enough without you and I discussing protocols and procedures, and for sure considering that it probably makes so little difference in the end results or the trends we might like to try and communicate and understand.
As you can see by the following overlay, there is a difference just like you suggest, but I doubt anyone would ever know the difference just using their radio.
View attachment overlay.pdf
Homer has a radar like sense for signals and audio from his radio, so he might be able to perceive this small a difference in rejection, and maybe to a little less degree with the gain, but most would never realize this kind of value difference. This is why I use the words "likely" and "OK" when I posted above.
These results weren't perfect and would not be what I preferred, but they were good enough and maybe better than just words.
I was surprised that the model based on Homer's calculator came out with such a good SWR too. I did not tweak the model to get it there, I just used the dimensions he referred to. Why would I change the specs, if I was trying to duplicate what Homer described?
I didn't go further into the model either, and for the same reasons, but I didn't say anything hoping to avoid confusion and upsetting folks and see the thread stop,
which I venture a wild guess will happen soon.
