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Antenna placement - RF Cafe Forums

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Below are all of the forum threads, including all the responses to the original posts.


 Post subject: Antenna placement
Posted: Fri Apr 07, 2006 6:13 pm 
 
Captain
User avatar

Joined: Fri Apr 07, 2006 6:10 pm
Posts: 18
Hello,

Does antenna placement significantly affect the radiation pattern of an antenna?

For example, I have a dipole connected to a metallic box. Will the dipole pattern change? Or say I have one of those TV antennas, if I place it on a different section of the roof or a different part of the house, will that affect the radiation pattern?

Thanks!


 
   
 
 Post subject: Antenna positioning
Posted: Fri Apr 07, 2006 8:36 pm 
 
General
User avatar

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
In a word, yes.

Yes, any nearby conductor will affect your radiation pattern. That's why AM broadcasting stations put their antennas over damp ground - it acts like a reflector does for light.

Near enough, and it also affects the impedance the antenna presents to the transmission line and transmitter.

Good Luck!
Fred


 
   
 
 Post subject:
Posted: Sat Apr 08, 2006 10:12 am 
 
Captain
User avatar

Joined: Fri Apr 07, 2006 6:10 pm
Posts: 18
Thanks! I got into this discussion because a classmate wanted to have a transmitter installed in his car. He said he was going to get this antenna that showed an omnidirectional pattern at his transmitting frequency. I told him that he should not go with the given pattern because the car's body will change the actual pattern. He said that he does not think that the car frame's frequency response is not the same as his transmitting frequency so he it should not affect the pattern.


 
   
 
 Post subject: Antenna pattern
Posted: Sat Apr 08, 2006 4:29 pm 
 
General
User avatar

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
Hi again!

The effect of mounting an omnidirectional antenna on a vehicle depends on the type of antenna, and where you mount it. A vertical dipole, in the center of the roof, will be omnidirectional. But most dipoles for lower frequencies are mounted on the fenders or the bumpers, and as a result will have a preferred direction. It's difficult to quantify without a lot of details and an analysis program. Still, bumper mounts are common among the amateur radio HF users.

Good luck,
Fred



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