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Antenna Placement?

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SCPD

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Feb 24, 2001
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65,126
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Virginia
Hello, I've noticed that most of the time antenna on public safety vehicles are located on the roof in the middle, or on the roof near the rear window. Depending on how many there are. Our public safety vehicles have two; so one is on the left its a VHF antenna for the statewide digital radio system and one if on the right; it's an antenna for the scanner. My question is, does it matter where they're mounted? I've seen them on trunks too, even on front hoods. Thanks.
 

nayr

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Dec 8, 2011
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35
Location
Denver, CO
if just one antenna the best place is going to be high in the middle of the car for good ground plane without any of the body in the way.

when working with multiple antennas, especially if they transmit you'll want to put em as far away as possible so they dont interfere. This typically means on opposite sides of the roof.

trunk and bumper mounts are when roof mounting isint a good option, they become slightly more directional.. ie, one mounted on the rear will pickup signals from behind better and vice versa.

thats the basic idea anywase

-R
 

KD0LWU

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May 17, 2010
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84
Location
Kansas
It doesn't matter as much if you aren't transmitting, when you are transmitting you are using the cars body as a ground plane to project the waves up and out, the more metal under it the better it will get out and be heard.
For receive it doesn't matter near as much, it does help some but probably not enough you would notice it.
 

n5ims

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Jul 25, 2004
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Larsen has a graphic with the results of their study on the various antenna mounting locations on a standard car. The first two pages of this (http://www.repeater-builder.com/antenna/pdf/larsen-mobile-antenna-mounting-and-designations.pdf) show the results of this study. Basically they take a drilled NMO mounted antenna on the center of the roof as the standard and list the amount of loss in dB for the various other types of mounts (NMO, glass mount & magnetic mount) as well as location.
 

SCPD

QRT
Joined
Feb 24, 2001
Messages
65,126
Location
Virginia
Antenna placement

Around here, the following is pretty much the truth:

The roof is where the radio shops put the antennas for the first install.
The trunk is where the DPW's put the antennas when moving equipment from an old vehicle to a new.
 
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