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-   -   Mobile antenna grounding (https://forums.radioreference.com/amateur-radio-antennas/352065-mobile-antenna-grounding.html)

KK4JUG 04-21-2017 2:45 PM

Mobile antenna grounding
 
I've always heard that "grounding is grounding" (except when it comes to lightning) but is that always the case when it comes to a normal ham radio antenna setup?

I'm wanting to ground my vehicle ham radio antenna to improve 6 meter transmission and transmission. The antenna mounted on a luggage rack crossbar that is painted. Neither the mount nor the antenna is grounded because of that coating on the crossbar. Would it be better to run a ground wire from the antenna mount to a ground point, probably following the same path as the coax, or, would it be permissible to ground the PL-259 connector where it plugs into the radio using a more convenient ground point from inside the vehicle? The radio is mounted under the passenger seat with the control head attached to the side of the side of the console.

The radio is a Yaesu FT-8900D and the antenna is a Comet SSB14.

ko6jw_2 04-21-2017 3:23 PM

I have this antenna mounted on a trunk lip mount. It requires a good ground plane to work correctly. That needs to be at the feed point not at the radio. I would suggest looking at a different type of mount. It's pretty long for a luggage rack mount anyway. Do not confuse DC grounding which is best done at the radio with RF grounding which needs to be done at the feed point.

You want the car body to be the ground plane. To make this work well sometimes it's necessary to place copper braid between the trunk lid and the car body. You may have to experiment.

By the way the SSB14 is intended to be used on the FM portion of 6 meters. I've used mine on the low end of the band for sideband, but it's not too efficient for DX.

The sound plane is most critical for 6 meters, but also necessary for 2 meters and 70 cm.

KK4JUG 04-21-2017 3:34 PM

I understand the necessity for grounding 6 meters. That's why I'm wanting to ground the antenna. I have an SUV so obviously, the trunk mount is out. I went into it knowing that I probably couldn't get optimal results on 6 meters because of the antenna location.

However, based on your experience, I will ground it at the source in hopes of improving it.

Rred 04-22-2017 11:39 AM

I would suggest that especially in mobile installations, you need an antenna counterpoise--not necessarily a ground. "Ground" can mean an earth ground, a chassis ground, a counterpoise, etc., many different things. Actually what you are doing on a car or boat is "bonding" different pieces, not necessarily grounding them at all, unless your car tows a substantial plow blade to cut into the earth. Or as gasoline tankers used to do, drag a chain to ensure static was is charged to the pavement.

One layer of paint will not greatly interfere with the radio frequency energy from the antenna flowing into the car body and finding an efficient counterpoise. RF jumps that gap, treating it as a small capacitance, even though DC electricity might not be able to jump it at all, or be greatly reduced by it.

"Ground" is like "food", a very vague term really that covers many things, which are not at all alike.

KK4JUG 04-22-2017 3:50 PM

I do understand that "ground" is a nebulous thing. What works in my car may not work with the same equipment in last year's model of the same vehicle. I installed the radio knowing that 6 meters was probably going to be iffy. By the same token, I'm gonna try a few things that might make it better. At this point, I don't plan on making any substantial vehicle modifications. Someone jokingly mentioned dragging a chain like gasoline trucks used to do. Unfortunately, I'm old enough to remember those but don't believe I'll go that far.

I'm going to run a braided ground along the same path as the coax as far as possible and connect it to a ground and that might make a difference. It certainly shouldn't hurt. Like I told someone earlier, I want to get the numbers low enough that transmitting won't blow out the transmitter.

I'm not above installing a roof mount antenna using a NMO mount. A benefit of that will be to lower the altitude of the antenna about 5 or 6 inches. Right now, it a hair below 9 1/2 feet, (It's an SUV so no trunk mounts.)

Anyway, I'm taking all this information to heart, including the PMs. Thanx for the help, guys.

W9BU 04-22-2017 9:25 PM

The guy who maintains this web site:

KØBG.COM

is kind of a guru when it comes to mobile HF installations. Lots of good info on this web site, though it will take you some time to absorb it all.


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