Eznec5 1/4 wave mobile model

[Marconi]

This model is my first attempt to model a mobile 1/4 wave whip antenna on a simulated mobile body. The antenna is 72" above Earth. The mobile roof, below the antenna is 72"L x 54"W. The side body is 55" tall...leaving approximately 17" of ground clearance. There is no tail section included, but the hood is extended about 20" in order to give a slight direction to the model. This skewing, however, did not appear to change the pattern.

In my steps to make a model that was only similar to a Suburban...I stopped at the measurements noted above. As I increased the body dimensions, I noted that the model became more and more capacitive, thus it was necessary to make the radiator shorter...in order to maintain resonance at 27.205 mhz. This result was just as I would expect, even though I find lots of folks disagreeing with my ideas on the subject. Both my Eznec models and my real life antenna work, using 1/4 wave radiators, seems to agree in this regard, so I figured I'd post this up and get some feed back.

IMO, the length of a mobile 1/4 wave radiator depends, to a large degree, on the effectiveness of the attached ground plane, and for sure in a lossy automobile installation close to the Earth.

The match and the other antenna characteristics for this antenna system developed to be just about what one might expect, assuming a suitable ground plane was attached. I also noticed nothing unusual with the results as compared to my own personal work with real live models using a 1/4 wave radiator and elevated radials and mobile installs.

View attachment Mobile simulated.pdf

 

[Henry HPSD]

Eddie,

Anyone who thinks the resonant frequency of a antenna is independent of the ground beneath it has lack of antenna knowledge.
That would be equal to those not taking diameter into mind.
Resonant doesnt mean efficient by the way.

Your foundings are those found by other before.

Remember you should moddel the entire car instead of the roof as the far field stretches futher than the roof. I know it might not have been your intention..but you know...
I think i have a car model (perhaps a couple) ill send them too you.

My appologise for not answering your mail regarding your 5/8 wave.
What you could do here on forum is give the average gain, in that way the "pro" guys have a indiaction how accurate it is.

For that and other reason i dont have "faith" In a topic "eznec" files.
You must be aware by now ,it still is a computer programm and you need to know what your doing. one just cant say..this is it cause Eznec tells me it is.
No...this is it cause i have asked Enzec to show me this, heck there comes another guy with only the demo programm not inserting material loss etc etc.
So infact it could be a bit different.
Just a half hour ago.. if got a guy asking question for a 5 elements LFA moddeld with NEC2 instead of NEC4. He is showing azimuth plot with ground gain he is expressing the immens gain figures...well you know...rubbish...

But back to yours, I notice your segmentation length are not equal.
It is wise to change your segmentation length.
Enzec likes those wires who have the same segmention length.

As you might have noticed yourself you tend to be bussy with trying to push as much gain from a simple vertical where the "average gain" tells you are beyond accurate.

As usual...
Marconi, KEEP UP THE GOOD WORK!

Kind regards,

Henry
All about antennas

 

[Marconi]

Thanks Henry, I got your mobile models. I'll check them out. They're a lot more complicated than mine. That's why I didn't go farther into this mobile model.

I'll work with the segments and see how that affects the gain. I had not thought about the actual gain regarding mobiles before, but my model shows a little negative gain...which I figured might be about right for a Mobile install so low to the Earth. Rather than my trying to maximize gain, I did nothing consciously to affect the gain. I just tweaked the model for no Eznec Geometry or Segment errors, and let the gain show what it would show.

The only thing I consciously did regarding segments was to try and make the segment length for each wire about 1' foot in length, but in looking back I did make some mistakes. At least one wire (#4) did not fit that idea, but on correction...it did not affect the results as I could tell. I typically might make the radiator show more segments in order to get the source closer to the position I think it should be however. I did that in this model.

I'll, of course be trying to improve my model. Your models will likely help me a lot in that regard. To start, I had nothing to go on in my thinking and you're right, I don't really know if what I do is correct of even close, but I have to believe...if the model results are not out in left field somewhere, the Eznec model works with no errors indicated, and the AG produces numbers close to a value of 1.0, then maybe I'm close.

I do think I learned something about the use of segments that I didn't understand before. This was after trying to duplicate some of Cebik's work in a report he did on the 5/8 wave Mystique a while back. He did not publish his actual use of segments or indicate the number used, but I think he really pushes the use for more segments than I had made a practice of using. I have not applied this idea to my mobile model as yet however.

A while back I asked MrSuburban for a copy of his mobile model, but I never heard back. I should have emailed you, it could have saved me a lot of steps.

BTW, my Average Gain is: 0.861=-0.65db
The free space model shows 1.12 dbi @ 30* degrees

 

[Needle Bender]

id like to see what the model looks like with a a99 on top of the car roof. thats what i do when i go camping. i have a big plate of steel and a welded 1 foot tube in the middle that i mounted 4 large magnets to it so it holds the antron up to about a 35 mile wind. if its more windy i use fishing line from the 3/4 way up to guy it 3 ways

 

[Marconi]

id like to see what the model looks like with a a99 on top of the car roof. thats what i do when i go camping. i have a big plate of steel and a welded 1 foot tube in the middle that i mounted 4 large magnets to it so it holds the antron up to about a 35 mile wind. if its more windy i use fishing line from the 3/4 way up to guy it 3 ways

NB, here I took my mobile model and made the center mounted radiator for a 1/2 wave and a .625 wave approximate. This was done by a change to the length only.

The descriptors are written by hand and showing Eznec Average Gain values for the models and the radiator lengths are in the details.

View attachment NB's mobile project.pdf

NB, if you try these both out, please let us know the results and if they appear to respond similar to these models, OK?

 

[Needle Bender]

i dont understand why the 1/2 wave is shows less than the normal 2dbi that a 1/2 wave usualy does. i have used that with great sucess once when camping at the beach. i talked all over hawaai and australia with the a99 right above the roof and a 2970. i dont have a imax to try it with a 5/8 yet.
thanks for doing that marconi, i dont care what they say about you, your a good guy

 

[Marconi]

i dont understand why the 1/2 wave is shows less than the normal 2dbi that a 1/2 wave usualy does. i have used that with great sucess once when camping at the beach. i talked all over hawaai and australia with the a99 right above the roof and a 2970. i dont have a imax to try it with a 5/8 yet.
thanks for doing that marconi, i dont care what they say about you, your a good guy

Not with standing proper data input and limitations, I don't know exactly how Eznec determines what it does, but remember these antennas are only 72" above the ground. If I were to just set them 72" above the Earth without the vehicle, I would expect about the same response. IMO, the answer to your question has to do with the low height.

It is more surprising to me that the 5/8 wave responds even worse than the 1/2 wave at this height.

It's always nice to be able to work DX if conditions permit, but such radio responses are almost totally dependent on conditions, unlike local contacts. I'm not always successful, but for this reason alone I try to avoid DX conditions when testing my antennas.

 

[Needle Bender]

it just seems wierd that it shows less than 2dbi for a 1/2 even if it was right on the ground its still a 1/2 wave and i thought a 1/2 wave always had that much gain because its a 1/2 wave not because the ground was close or far. i wonder if ezenc has some qwirks

 

[Henry HPSD]

Now we are getting there guys...
wierd isnt it ?

In order to compare antennas we should start by doing that in "freespace".
Thats the only "non- exsisting" world in which all secondary aspects are equal.
There can we find the gain expressed by Needle bender.

Afterwards we then apply the model into the real world, cause different outcomes will be generated.

This cause:
Antennas are influenced by the number of radials and length (this also goes for our 1/2 wave vertical though not that much as others).
And they are influenced by heigth above ground and the ground type they actually are above.
One has to bare in mind the "earth losses.." Material losses etc.
A dipole has "only" 2,14 dBI in freespace.


To answer needle bender his question:
Everybody knows a dipole has 2,14 dBI.
However ! it can be as low as a actually negative gain value and can be as high as around 8 dBI under the rigth situation.
(Thats due to those "interactions" mentioned above ..earth etc..)
The "rigth" situation would be for example on a boat in a salt see.
Just lissen to some ocean going maritime mobile station....always strong..
And try to do the same thing in the middle of the sahara desert...zzzz

Just another thing where people often are wrong...a dipole isnt 70 Ohms or whatever...it can be almost anything from 10-100 ohms depending on height above ground.

Its the abbility to get the "maximum" gain there where you want it to be, and
the mind set to see the antenna not only in the "freespace" world.. but also in a different "enviroment".

So, although a 3el beam can have 8dBi gain for example it would be quite easy to "create" a circumstance where a simple 1/4 wave vertical would outperform it on DX.

The best antenna is the antenna which has maximum gain under the angle you want it to be. That inst always the one with the highest gain value.

Kind regards,

Henry
All about antennas

 

[Needle Bender]

Now we are getting there guys...
wierd isnt it ?

In order to compare antennas we should start by doing that in "freespace".
Thats the only "non- exsisting" world in which all secondary aspects are equal.
There can we find the gain expressed by Needle bender.

Afterwards we then apply the model into the real world, cause different outcomes will be generated.

This cause:
Antennas are influenced by the number of radials and length (this also goes for our 1/2 wave vertical though not that much as others).
And they are influenced by heigth above ground and the ground type they actually are above.
One has to bare in mind the "earth losses.." Material losses etc.
A dipole has "only" 2,14 dBI in freespace.


To answer needle bender his question:
Everybody knows a dipole has 2,14 dBI.
However ! it can be as low as a actually negative gain value and can be as high as around 8 dBI under the rigth situation.
(Thats due to those "interactions" mentioned above ..earth etc..)
The "rigth" situation would be for example on a boat in a salt see.
Just lissen to some ocean going maritime mobile station....always strong..
And try to do the same thing in the middle of the sahara desert...zzzz

Just another thing where people often are wrong...a dipole isnt 70 Ohms or whatever...it can be almost anything from 10-100 ohms depending on height above ground.

Its the abbility to get the "maximum" gain there where you want it to be, and
the mind set to see the antenna not only in the "freespace" world.. but also in a different "enviroment".

So, although a 3el beam can have 8dBi gain for example it would be quite easy to "create" a circumstance where a simple 1/4 wave vertical would outperform it on DX.

The best antenna is the antenna which has maximum gain under the angle you want it to be. That inst always the one with the highest gain value.

Kind regards,

Henry
All about antennas

seems the damn ground is always getting in the way