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Author Topic: truck rack antenna installation question  (Read 1187 times)
KJ6MEV
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Posts: 84




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« on: September 06, 2012, 06:41:47 PM »

 I'm planning on putting some hamtennas and maybe
a manual screwdriver on the truckrack, towards the rear
with the antenna mounts wired to the frame for a ground.
I don't want to overlook anything important.....so....
what's important?
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KE5PPH
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Posts: 73




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« Reply #1 on: September 06, 2012, 06:44:52 PM »

reading 30 pages of information in the MOBILE forum
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KJ6MEV
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Posts: 84




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« Reply #2 on: September 06, 2012, 07:33:22 PM »

 I found kobg has a great article on truck bed bonding
on his website. That's what I was looking for. Thanks.
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W8JI
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« Reply #3 on: September 07, 2012, 07:37:17 AM »

I'm planning on putting some hamtennas and maybe
a manual screwdriver on the truckrack, towards the rear
with the antenna mounts wired to the frame for a ground.
I don't want to overlook anything important.....so....
what's important?

What is important is to remember a ground is not a ground when it carries RF current.

When it carries RF current, it is an antenna.

No matter what you read, and no matter what anyone tells you, the area BELOW the feedpoint has the same current at the feedpoint as the area above the feedpoint. If you put a six foot tall mobile HF antenna on a 30 foot tall pole and connect the pole to the antenna and coax ground, the antenna becomes 36 feet long.

Very often you will see people claiming or assuming the shield side magically has no current.

So now think about what you are doing. You are grounding to the frame, which may be a good battery ground but is is really not a good RF ground.  That alone makes no sense, unless the vehicle body and roof is fiberglass or plastic.

What you want for an RF ground is a very SHORT lead, as wide as possible, to a large metallic area that is all spread out. A six inch lead to a metal trunk deck would be a much better RF ground than a six foot lead to a frame, or anything else. A ground to the major bolted or welded metal of a metal shell vehicle would be better yet.


I don't know where the frame myth comes from, but usually on passanger vehicles a frame floats. The body sits on rubber isolators to reduce road noise and ride harshness, or is just bolted at certain points.

On my F250 the frame is insulated from the body shell with only a few contact points. The bed has eight spread out bolted areas to the frame. The frame makes a terrible RF ground as the truck is shipped. The cab and the truck bed in particular make a much better ground.



http://www.w8ji.com/rf_noise_powerstroke_diesel.htm

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KJ6MEV
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Posts: 84




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« Reply #4 on: September 07, 2012, 09:49:59 PM »

ok w8ji,
  This all makes sense.... and this other stuff
I'm reading appears to take this all a step further, which
is to connect (with wide copper braid) the bed and cab to the frame
and exhaust and anywhere else one can make an electrical
connection (even the block). Apparently, this would make the ground plane even
more substantial. Am I understanding this correctly?
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N6AJR
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Posts: 9927




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« Reply #5 on: September 13, 2012, 11:21:30 AM »

I always use a braid from the ground side of the antenna to the chassis, or trunk lid or what ever is close for an exterior ground. I also run another short braid from the ground side of the radio to the floor or chassis, usually a self tapping sheet metal screw, and again I run a braid from the ground post of the battery to the chassis right at the battery, like on the fender near the battery.  also check you braids now and then because they will corrode.
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