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Author Topic: mobile antenna grounding  (Read 426 times)
KE6ANM
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Posts: 17




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« on: February 26, 2009, 02:36:12 PM »

I am installing new antennas on my truck and RV.
What kind of antennas cant be mounted on fiberglass and adhesive mounted on glass( not through glass) do I need to run a ground wire to the antenna mount.
I am mounting some diamond mobile dual band fold over antennas. am I ok, or do I need to run a ground.
perry
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W3LK
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« Reply #1 on: February 26, 2009, 02:58:00 PM »

You want a ground plane UNDER the antennas. That is not the same thing as a ground wire. Read www.k0bg.com - the sections on antenna installations.

This site will answer your questions.

73,

Lon - W3LK
Naugatuck, Connecticut
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N1LO
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« Reply #2 on: February 26, 2009, 04:48:48 PM »

Hi Perry,

Sounds like 2m/440 dual band antennas. Is that right?

They will definitely need a counterpoise to 'push against'. This can be accomplised on a FG body by installing wires or strips of copper foil tape on the inside of the body panel as close as possible to the base of the antenna. You'll of course need a bonding wire from the antenna mount to your counterpoise network.

If possible, bond a 38-40" long piece of aluminum foil to the body panel with spray adhesive and run a short (6-8" or less, if possible) jumper to the mount.

To make a connection to the foil, fold it over itself several times and put a machine screw with large washers through it or use an alligator clip.

If common foil is not possible, go by an arts & crafts store and pick up some copper foil tape and use that. Failing that, fan out as many 19" long wires as you can and run your jumper from their center to your mount.

Does this help?

Cheers,

Mark
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K0BG
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« Reply #3 on: February 27, 2009, 06:46:00 AM »

Counterpoise is the incorrect term, albeit used all too often.

All 1/4 wave verticals require a ground plane under them, including so called 1/2 waves. If you don't, there will be common mode currents flowing on the coax cable feeding the antenna. In most cases, especially with glass mounts, the coax does the majority of the radiating.

Instead of messing with half-baked antennas, bite the bullet buy a decent one, and drill a hole. If you just can't bring yourself to do that, then mount one on an angle bracket off the hood or trunk seam.

Alan, KØBG
www.k0bg.com
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K5END
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« Reply #4 on: February 27, 2009, 07:48:06 AM »

For a 2 meters on a fiberglass car as the poster mentioned, I'd be tempted to look at making a mobile 2 m dipole antenna.

There are some design challenges, yes, especially for a vertical polarization, but this is worth considering.

I recently built a portable 2 meter dipole that I can carry around. With a 5 watt HT (IC-V8) and a 6' length of coax, I can hold it at arm's length. It works better than I thought it would. I have not made laboratory measurements. But I can turn the HT down to 0.5 Watts and still activate repeaters more than 15 miles away. At 5 Watts I get "full quieting" on signal reports.

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WA3SKN
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« Reply #5 on: February 27, 2009, 09:22:26 AM »

What bands are you talking about, anyway... HF, VHF, UHF?  Describe what you are trying/planning to do.

-Mike.
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K5DVW
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« Reply #6 on: February 27, 2009, 09:37:23 AM »

Maybe you should drag an 8 foot ground rod behind the RV?
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N1LO
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« Reply #7 on: February 27, 2009, 02:01:17 PM »

So Perry, do tell us a little more about your installation and vehicle to refine our suggestions.

We got the fact that the vehicle has fiberglass panels, and the only dual-band foldover antennas I know of are for VHF/UHF.

Ignore the half-baked posts.

GL,

Mark
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KE6ANM
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« Reply #8 on: February 27, 2009, 06:29:12 PM »

I am installing a vhf uhf radio tmd 700a  in my Honda ridgeline, and a aprs microtraker tnc as well.
the RV is a tent trailer, with a solid roof.
it is a  Fleetwood evolution 3
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K5END
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« Reply #9 on: February 28, 2009, 05:45:06 PM »

Honda Ridgeline?

Me too,

This weekend I'm working on getting power through the firewall.

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N1LO
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« Reply #10 on: March 01, 2009, 09:49:11 PM »

For the trailer, I'm imagining a rectangular fiberglass roof with 4-6" sides. I think you could mount your antenna on the side, with a 38" long piece of aluminum foil tape along the side, centered on the mount. Add a short jumper from the foil to the mount.

I'll have to look at some pictures of the Ridgeline before I comment on that.

Mark
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