I modeled my ford explorer.

I created a model based off of the dimensions of my ford explorer.

This is what the model looks like with a 1/4 wavelength antenna on the middle of the roof.

I have three models based on this object, one with the antenna on the middle of the roof, as pictured above, one with the antenna on the middle back of the vehicle, and one with the antenna about where it is on my vehicle, which is between the other two. I also have a model of a 1/4 wavelength ground plane antenna with horizontal radials at the roof height.

The vertical plot (the pattern as seen from the side of the vehicle), the front of the vehicle is to the right (the 90 degree mark) of this plot.

The horizontal plot (the pattern as seen from above the vehicle), the front of the vehicle is at the top (the 90 degree mark) of this plot.

The antenna mounted on the middle back outperformed the other antennas in the forward direction, including the 1/4 wavelength groundplane reference. My setup is, not surprisingly, between the center and middle back mounted antennas as far as forward radiation goes. As is expected, as you move the antenna towards the back on the vehicle, the pattern shifts more towards the front. An interesting thing to note is the antenna mounted on the middle of the roof actually has more gain to the back of the vehicle than the front, bot not so much that you will notice.

Any other thoughts on these plots?

Here is a link to the .NEC file I used if you want to play with it.


The DB

 

[rizzjc]

Cool! I've not played with the antenna analyzer. Something that's always been on my list. I do wonder if you're able to take into account that it's a vehicle, and not the ground, and how much difference that makes. I see you modeled the shape of the vehicle, but does it know that it's a car, sitting on tires, above the ground? What if you modeled the same antennas to a ground reference, and compared?

 

[The DB]

The bottom of the model itself is above the ground by a foot, so it is not connected to ground at all.

Connecting the antenna to the earth below generally makes little difference in models unless there are common mode currents present on that line.


The DB

 

[The DB]

As I know some people mount an antenna to a mount that bolts to the top of the back left tail light, I modeled an antenna at that location, for forward gain, it outperformed all other antenna locations I have, as of yet, tested. This surprised me, as the part of the antenna that radiates the most is shielded by part of the vehicle... The difference seems to be the antenna's efficiency, a full length 9 foot antenna is more efficient at that location than on the roof, which is also surprising, most vehicles that is the other way around...

It might be worth me moving my antenna to that spot... Now I wonder about dual antennas in that location... Hmm, it might actually clean up the pattern some...


The DB

 

[The DB]

For those interested, here are the models from the back left light mount, and a set of duals mounted from both rear lights.

The pink pattern is a standard 1/4 wavelength groundplane antenna mounted at roof height. The green pattern is the antenna mounted at the back of the roof from the previous model set, in that set it produced the most forward gain. The red pattern is a single 1/4 wavelength antenna mounted on amount that bolts to the top of the left tail light, as some people mount antennas on 2/nd gen models. The blue line is a set of dual antennas mounted on the mounting bolts of both tail lights.


The DB

 

[rizzjc]

Interesting. Although there is definitely a difference, I think this shows that tout can't really go too wrong placing the antenna where it works best for you. Unless in reading it wrong, it just doesn't seem like enough difference to even worry about. The tail light mounts definitely show the most degradation to the sides though. Good stuff!