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Author Topic: Mobile RFI  (Read 441 times)
K0BG
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« on: February 04, 2002, 12:28:38 PM »

For some reason which escapes me, the majority of amateurs flat refuse to properly mount mobile antennas on ball mounts or other bolted-to-body mounts. Using flimsy license plate mounts, trunk lip mounts, and similar devices to install mobile antennas are prescriptions to all matter of RFI, EMP noise, and poor operation in general.

In addition, improper grounding of doors, hoods, trunks, exhaust and tail pipes, fuel lines and anything bolted on is a recipe for QRN.

Do yourself a favor; take time to properly and safely install your rig and antenna using proper mounts, and ground everything that's bolted, clamped, or clipped on.

My 1998 Mercury Mystique with ball-mounted antenna has virtually no RFI hash or EMP noise except on 10 M and then only while under heavy acceleration.
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N3MG
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Posts: 27




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« Reply #1 on: February 12, 2002, 05:29:58 PM »

Alan-

Point well taken. I recently completed the installation of a 706 in my Toyota Tundra and grounded virtually everything to the frame i.e. hood, bed, doors, engine block, exhaust pipe, etc.

Only problem was RF getting into the separation cable...apparently a common problem that was cured easily with a ferrite toroid at either end.

My biggest problem is RFI/EMI from nearby vehicles, powerlines, and signs.  An urban environment is TERRIBLE for noise, and adds to the challenge of HF operations.

Mark
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K0BG
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« Reply #2 on: February 21, 2002, 10:00:54 AM »

I agree with you on exterior noise. One thing I've tried which works for some kinds of exterior noise is a ground strap. You used to see these alot when all of the seats were made of nylon with wool under-support pads. I found a new one at a swap fest a few years ago. It didn't completely cure anything, but it did help a little.

What I'd like to find is an axle grounding spring like Detroit used to use. They were a little sprial spring mounted inside the wheel bearing cup and had a bronze contact riding against the axle. My FWD Mercury doesn't have them, and the way the sealing caps are made, I'm not sure you could fashion one or not. As I stated before, I only hear this static on 10M, and only when moving. Oddly enough, I don't hear it on 6M, but here it could be masked by the nominal band static. Hard to say.

How do you have your antenna mounted? Mine's solidly mounted on the left quarter panel with a heavy-duty ball mount made by Master Mobile years (35+) ago.
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N3MG
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Posts: 27




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« Reply #3 on: February 21, 2002, 11:44:58 AM »

Here's a link to my webpage showing my 706 install.

http://www.fastq.com/~louvu/mobile.htm

Regarding ground straps, I also grounded my stake pocket mount to the bed again with 1" braid.  I didn't shoot a photo of that...the strap is off the bolt that comes up through the bottom of the stake pocket.

The Diamond antenna that I am using does not require a ground plane per se.  I wanted a ground there as I also have an NMO to 3/8" stud adapter so I can change to s/s whips or even another HamStick. I know other guys that also have the NMO to UHF adapter, so when they reach a campsite, e.g., they can run a length of coax off the antenna mount to a dipole in the trees without having to mess with the back of the radio.

If anyone is interested in my Custom Tundra Stake Pocket Mount, they can visit

 http://www.fastq.com/~louvu/antmount.htm

73
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KE4RQ
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Posts: 5




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« Reply #4 on: May 16, 2005, 01:44:57 PM »

Just starting to put a mobile rig in my Tundra and found your posts.  The weblinks to your pictures don't work; is there an alternative site?

73,

Clark
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N3MG
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« Reply #5 on: May 17, 2005, 10:15:58 AM »

Clark-

I submitted my set up to K2BJ's website in 2002. The link is below. The old webpages are down as I have since moved from Arizona. Still, the photos and write up should help.

I still have the Tundra and operate mobile here in Hawaii.

73 and Aloha-

Mark WH7W (ex: N3MG)

http://www.k2bj.com/MOTM_archive/0206MOTM.htm
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KE4RQ
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« Reply #6 on: May 18, 2005, 01:08:28 PM »

Thanks for the link.  Really helped me visualize what I can do.

I noticed you made reference to power distribution through an audio power block fed by 4 ga.  Where did you pierce the firewall in your Tundra to bring the power into the cab?  I assume the 4 ga. is brought into the cab and the block is mounted somewhere, right?

73,

Clark
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WA5UHK
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Posts: 131




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« Reply #7 on: May 26, 2005, 04:12:23 PM »

N3MG,

I had RFI also with my Sequoia. It is basiclly a Tundra.  What killed it was a double short straps from the Cab/unibody to the frame.

In particular, I put straps immediately under the place I had the radio mounted and grounded...drivers seat.  Also, I bonded the unibody and frame as close to the antenna mount as I possibly could; 9" double 1/2"copper braid.  These two places stopped the RFI on 20mtr transmission and on 40 mtr transmission.  I've not installed 10 and 15mtr yet.
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WA5UHK
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Posts: 131




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« Reply #8 on: May 28, 2005, 10:25:32 PM »

Just noticed the question on the firewall.  I have a Sequoia; similiar to Tundra.  I brought two conductors through the firewall just to the right of the steering wheel (if your standing outside looking under the hood) at the same level as the the mount for the steering wheel on the firewall inside. I used bushings on both and split sleeving.

I put two distribution blocks, one for pos and one for neg, on a plexiglass plate and then mounted the plate to the panel so the parking brake pedal just clears them.  Of course I fused at the battery.  I can remove the plate and both blocks are accessible to add runs.

I used #8 copper and 45amp fuses.
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