4nec2 I have a idea

[davev8]

Hi i have had go at using this antenna Design software and i just cannot get my head around it:headbang
What i need to know is how you get a idea of a antenna thats in my head and model it in 4nec2
The antenna i want to model 1st is a 5/8 wave vertical (@27.555 mhz)
with the radiator made out of ally tube
and 3 wire 5/8 ground planes and matching it with a sigma 2 type ring (as i can make them work well with 6 feet of copper tube)
I am using the above antenna now but with estimated length and angle of the ground planes
and i want to model it befor i make the mk 11
MY IDEA
If some clever bod was to make a you-tube vid starting from the beginning (from clicking on the 4nec icon) showing how to use this fantastic bit of software i think this thread will become a sticky very quickly
Thanks dave

 

[Marconi]

Hi i have had go at using this antenna Design software and i just cannot get my head around it:headbang
What i need to know is how you get a idea of a antenna thats in my head and model it in 4nec2
The antenna i want to model 1st is a 5/8 wave vertical (@27.555 mhz)
with the radiator made out of ally tube
and 3 wire 5/8 ground planes and matching it with a sigma 2 type ring (as i can make them work well with 6 feet of copper tube)
I am using the above antenna now but with estimated length and angle of the ground planes
and i want to model it befor i make the mk 11
MY IDEA
If some clever bod was to make a you-tube vid starting from the beginning (from clicking on the 4nec icon) showing how to use this fantastic bit of software i think this thread will become a sticky very quickly
Thanks dave

Hello dave8.

I don't know 4nec2, but here is my Eznec5 model of a 5/8 wave antenna at 27.205 mhz, with 4 x 5/8 wavelength horizontal radials vs. 4 x 5/8 wave 1/4 wave radials at 8.5' feet length, and according to the model your idea doesn't look good. IMO, if you're seeing good results with this design, then it's just a fluke of nature.

Not only is the pattern's primary lobe skewed primarily to a high angle near 55* degrees, it also shows negative (-) gain at the horizon. This is probably due to the considerable current flowing in the radials elements and thus on the mast and feed line. It appears that this magnitude of current probably exceeds that flowing on the radiator and that is not good either.

IMO, this is a common problem with vertical radiators with too much horizontal ground plane, and is supported somewhat by what theory has claimed in this regard for the past 70 years or more, so I wonder why try to change theory.

View attachment I-10K with 5_8 vs. 1_4 wave radials..pdf

 

[gamegetter]

What length of radials are you using davev8?

Marconi, wouldn't the longer ground planes reduce the current on the 5/8th? Or up to what length?

 

[Marconi]

What length of radials are you using davev8?

Marconi, wouldn't the longer ground planes reduce the current on the 5/8th? Or up to what length?

gamegetter, I read dave8 to say his model idea had 3 x .625 wl radials. At least that is what I modeled and posted using my standard model for the I-10K. BTW, the I-10K model is not designed to specs for the I-10K. I just made a 5/8 wave model that is made up of a 22.5' foot long radiator with 8.5' foot radials, and no tapper.

I'll have to redo the model I made with longer radials, and then check the currents data detail to know for sure. I think you may be right, if you're suggesting that adding radials 5/8 wl long will somehow reduce the current flowing in the 5/8 radiator.

IMO, if you wanted to improve gain a bit, then adding more radials may be the way to go, rather than adding length much beyond about 1/4 wavelength.

 

[davev8]

What length of radials are you using davev8?

i don't know the length of the radials as the antenna was made in less than 1 hour befor it got dark and as i remember reading sumplace that a wire will need to be longer than a pole say 1 inch across to be electrically the same (or was it the other way round ) i told my son to lay the wire alongside the radiator and cut them a foot longer, the radiator was lengthened 18 inch to be set at 5/8 wave at 27.555 so 12 inch longer than this.
But i think the important bit is the 5/8th wire radials are steeply swept down maybe only 25 or 30 degrees from vertical
The mounting pole is approx 15 feet long mounted on my roof (brick) and is not insulated from the antenna
i want to try insulated and uninsulated mast when i make the mark 11
The mark 11 will be 60 feet at feed point
Feed point is only 35+ feet high now
I am at sea level in the open and the land will be classed as good
As i have not had a CB for long time, so no buddy's to take s readings from.
But in my part of the UK when this antenna was a standard no name silver rod type 5/8, at night i had typically 2 or 3 stations at best in the back of the box, after the mods this went up to 4 or 5 and maybe 20 stations unreadable but definitely their now that was not before
No way scientific but i was encouraged by the results
The bandwidth seams vary wide, as my rci 2970dx had not arrived i swr it with a 80 channel fm rig, mid band and UK40 with swr at mid band channel 40 of slightly less than 1-1.2 and slightly more than 1-1.3 on mid channel 1 and the same on channel 40 UK fm
off the top of my head the must be almost 1mhz span

Thanks dave

 

[gamegetter]

Sorry if i missed this, but at what height above ground will you be installing the antenna?

 

[gamegetter]

that software is giving me all kinds of fits, can you model that marconi? i'll keep trying it a while longer.

 

[Marconi]

dave8 the model I posted was at 40' feet to the feed point and according to Eznec5 was over real Earth for both models. Maybe I misunderstood your measurements and that would make some difference, and I did not notice that you slanted the radials down and that too will make some difference.

I can slant the radials down and make then 23' feet if you wish and scan a new pattern. Maybe it will make the positive difference you saw in real life. I have heard folks claim the same as you, that the 5/8 wave radiator with 3-4 x 5/8 wave slanted down radials showed improvement in gain and response, but I think I've done this before with a simulation of an Imax, and the model did not show the improvement reported.

Give me a good guesstimate as to the angel and I go from there using 23' feet length, OK?

 

[davev8]

[QUOTE

Give me a good guesstimate as to the angel and I go from there using 23' feet length, OK?[/QUOTE]

25 or 30 degrees from vertical

 

[davev8]

Sorry if i missed this, but at what height above ground will you be installing the antenna?

now its over 35 feet but will be 60 feet when my mast is finished

 

[Marconi]

Well dave8, looks like you might be right, except for one big issue.

I made the radials slanted to 35*- 40* degrees, and the pattern and the gain look very good, with a nice full high gain RF lobe from 25* to 30* degrees with a small null showing gain @ 4.31 dbi at 18* degrees which is not bad.

The Eznec pattern shown (your idea) should be very useful, but the current flowing on the mast has to be dealt with in some effective manner and if so...that may ill-affect this pattern. So, if you're out in the country side with no neighbors to bother, I would not worry about these currents that might make TVI.

Notice the heavy current flows on the mast compared to the previous patterns posted, and in particular compared to those on the I-10K with 1/4 wave radials that are horizontal. I'll do another model with 1/4 wave radials slanted down, and post that too.

View attachment I-10K with 5_8 radials slanted.pdf

 

[Marconi]

Well dave8, looks like you might be right, except for one big issue.

I made the radials slanted to 35*- 40* degrees, and the pattern and the gain look very good, with a nice full high gain RF lobe from 25* to 30* degrees with a small null showing gain @ 4.31 dbi at 18* degrees which is not bad.

The notations above: ...25* to 30* degrees...should read 5* to 30* degrees.

 

[davev8]

Thanks Marconi
So i did make a step up from the original antenna that was 18 inch shorter and no radials then

What id like to do is get a sirio 827 try it stranded then with the long radials
and then compare it with the new vector 4000 which is the antenna i will end up with


Marconi..........if i ask nicely......... is it possible ..........that you might do a you-tube vid on how to get started with eznec

Thanks dave

 

[gamegetter]

Well dave8, looks like you might be right, except for one big issue.

I made the radials slanted to 35*- 40* degrees, and the pattern and the gain look very good, with a nice full high gain RF lobe from 25* to 30* degrees with a small null showing gain @ 4.31 dbi at 18* degrees which is not bad.

The Eznec pattern shown (your idea) should be very useful, but the current flowing on the mast has to be dealt with in some effective manner and if so...that may ill-affect this pattern. So, if you're out in the country side with no neighbors to bother, I would not worry about these currents that might make TVI.

Notice the heavy current flows on the mast compared to the previous patterns posted, and in particular compared to those on the I-10K with 1/4 wave radials that are horizontal. I'll do another model with 1/4 wave radials slanted down, and post that too.

View attachment 4930

hey old grandpa, i had you on my receive yesterday afternoon on the drive at five, but i could not make it back to you, conditions closed fast...conditions better today.

thanks for modeling that, if i get that 4nec2 software figured out, i'd like to see if there is some distance between 1/4 wave and 5/8 ground planes that would reduce current, that has been on my mind too.

Also and I'm sure it won't make that much difference ? but the frequency he needed was 27.555

73's

 

[Marconi]

Thanks Marconi
So i did make a step up from the original antenna that was 18 inch shorter and no radials then

What id like to do is get a sirio 827 try it stranded then with the long radials
and then compare it with the new vector 4000 which is the antenna i will end up with

Marconi..........if i ask nicely......... is it possible ..........that you might do a you-tube vid on how to get started with eznec

Thanks dave

Dave, I don't know what you are trying to say in paragraphs one and two above, but regarding your last remark, I've been trying to develop the process for doing a modeling demo video, but thus far I haven't had any success getting the screen shots nice and visible for the viewer. With my lack of video skills and my trying to work with screen shots of the Eznec5 software...is not as simple as it might seem.

I'll note hear how I finally managed to get past the most basic hump in understanding of Eznec Demo data entry. I had tried to understand this product several times before, but with no luck.

So, I emailed a forum member and asked him to email me his file of a Starduster model he had posted and discussed on the forum. Then I was able to see and visualize how the data entry was done, and then I was able to manipulate simple models and learn how and what the functions, features, and output features were all about.

Then I read the manual over and over again trying to understand more and learn how Eznec5 handles its own error checking. Like anything else, it matters how much practice one does.