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Re: [TowerTalk] Mobile antenna for SUV

To: "Tower Talk List" <>
Subject: Re: [TowerTalk] Mobile antenna for SUV
From: "Jim Brown" <>
Date: Mon, 26 Mar 2007 07:55:40 -0700
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On Sun, 25 Mar 2007 16:21:43 -0700, Bill Turner wrote:

>My choice would be a roof mount right in the center of the vehicle and
>to use Hamsticks. 

Yes. I have been quite pleased with Hamsticks. Not as convenient as a 
screwdriver, but they work fine if you install them well, especially on 
the higher bands.

The key to a good mobile antenna is a good ground to the body (so that 
it can act as a counterpoise for the antenna). And that can be VERY 
difficult in many of today's cars. My 2006 Toyota Sequoia has AWFUL 
bonding of the body -- for all practical purposes, it isn't bonded at 
all! That is, the parts of the body aren't electrically connected 
together because there's paint in the way. There are two problems with 
this. First, the antenna doesn't work very well. Second, you can drive 
your electrical system nuts (and the computers that run the car) 
because they  aren't properly grounded. 

I mounted my Hamstick to a clamp that mounts onto the luggage rack, and 
ran a piece of RG58 with braid and shield tied together from the mount 
to the screws that secure the luggage rack to the body. That works fine 
as an antenna. BUT -- the body bonding problem causes RF to get into 
the car's computer, and causes SERIOUS problems with the drive train 
(like the SUV won't go over 15 mph). I haven't had time to solve that 
problem, which will probably require screwing a lot of body parts 
together, etc. 

The bonding problem, of course, will vary from one vehicle (and mfr) to 
another. To get a handle on YOUR vehicle, poke around it with a good 
VOM on the low ohms scale, measuring from one body screw to another. 
I've measured tens of ohms between two points only a few feet apart. 
Even the bond between the battery and the chassis is stinko! 

Another point. Grounding the RADIO chassis to the body is NOT 
important. But it IS critical to run both hot and return POWER leads 
straight to the battery. And I also recommend using some SERIOUS 
ferrite chokes (beefy, single turn) on the hot lead so that it doesn't 
put RF on that DC line. 


Jim Brown K9YC


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