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Author Topic: Just bought one of those three magnet antenna mounts.....  (Read 5210 times)
K3NRX
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« on: June 04, 2012, 03:03:38 PM »

....and the spoiler on the trunk has spoiled the purchas as I am out of room.....(2007 G6)......I am under the impression that all three magnets have to be on the full surface of the metal.....anyone have any suggestions?Huh.....that doesn't involve putting it on the roof??? (as the 10 meter hamstick I use is long enough)....and for the record, the spoiler is not removable......

V
KA3NRX

« Last Edit: June 05, 2012, 10:36:47 AM by KA3NRX » Logged
WD5GWY
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« Reply #1 on: June 04, 2012, 05:04:54 PM »


Yes, all three magnets need to be in full contact with a metal surface.
Anything less, will increase the chances that the antenna will fly off the vehicle
while in motion. (not a good thing) If you just cannot bring yourself to drill holes
in the metal for a side mount (rear fender quarter panel), or some other type of
mounting scheme that is much stronger, then the mag mount is your only choice.
Good luck.
james
WD5GWY
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KE5PPH
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« Reply #2 on: June 04, 2012, 07:13:29 PM »

Is the trunk lid real Ferrous metal? I've seen 2 different guys, using a modified strap on bike carrier as a mount. I liked it becuase you could basically roll it up and toss in it the trunk, for short parking garages and security.
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W8JX
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« Reply #3 on: June 06, 2012, 05:09:41 AM »

....and the spoiler on the trunk has spoiled the purchas as I am out of room.....(2007 G6)......I am under the impression that all three magnets have to be on the full surface of the metal.....anyone have any suggestions?Huh.....that doesn't involve putting it on the roof??? (as the 10 meter hamstick I use is long enough)....and for the record, the spoiler is not removable......
Quote

Well the leading magnet is the critical one so to speak (the forward one). How much contact area are you lacking?
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WX7G
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« Reply #4 on: June 06, 2012, 07:36:49 AM »

Can you modify the mag mount by moving the magnets inward and cutting off the excess metal? It should be mounted with two magnets toward the front of the vehicle.
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W8JX
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« Reply #5 on: June 06, 2012, 08:33:23 AM »

Can you modify the mag mount by moving the magnets inward and cutting off the excess metal? It should be mounted with two magnets toward the front of the vehicle.

good tip
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N6AJR
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« Reply #6 on: June 06, 2012, 10:40:18 AM »

I have a 3 and a 4 magnet set, and they are going to scratch the snot out of your paint.  get a nice antenna and punch the hole in the deck lid.
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W8JX
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« Reply #7 on: June 06, 2012, 10:52:00 AM »

I have a 3 and a 4 magnet set, and they are going to scratch the snot out of your paint.  get a nice antenna and punch the hole in the deck lid.

Depends on magnet, If bottoms are smooth and you make sure they are clean and roof is clean very little scratching will take place. It is important to not slid it loose but rather tip/lift it loose. Sliding it will scratch car.
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K3NRX
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« Reply #8 on: June 07, 2012, 09:48:14 AM »

Can you modify the mag mount by moving the magnets inward and cutting off the excess metal? It should be mounted with two magnets toward the front of the vehicle.

Yes...Looks like I can, IF I drill holes a few inches in from each hole where the magnets are bolted....I have a friend who has a Machine Shop Drill (that dates back to the 1940s) that I can probably use.....Great idea, but I am a little concerned that there is some physics formula that will dictate that the magnets won't hold at high speeds because I moved them inward a few inches.....any of you science/math nerds out there think that would be an issue???........Under no circumstance do I want this thing flying off the car.....

V
KA3NRX


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W8JX
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« Reply #9 on: June 07, 2012, 09:57:33 AM »

I do not see a problem but if you are concerned merely attach a piece of fishing line to front of it at top of fiberglass stick and to car somewhere to limit wind loads at high speed. Antenna will see less total drag on trunk that on a roof mount.
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M6GOM
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« Reply #10 on: June 07, 2012, 10:37:17 AM »

Under no circumstance do I want this thing flying off the car.....

V
KA3NRX




Before I got a lesson in why you drill a hole, I used a triple magmount. With two magnets forward and one to the rear it was fine with a Little Tarheel II with a 60" whip extended quite far on 80m driving at 70MPH into a headwind.
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K3GM
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« Reply #11 on: June 07, 2012, 12:20:00 PM »

The magnetic mount also provides capacitve coupling between the sheet metal and the grounded side of the antenna.  Lifting the mount eliminates that intimate contact, and you will develop all sort of ground problem within your system.

In my opinion, Hamsticks and permanent mounts like the NMO don;t play well together.  An overbranch can easily distort or even rip the mount from the thin sheet metal.  For the roof of my Tahoe, on 10 meters I use a Larsen NMO27 coil with their thin stainless steel whip which is very compliant to overhead limbs and drive-thru banks.  If you decide to make a hole, a 3/4" Greenlee punch, or Antennex hole saw is recommended.  You only get one chance, so I recommend using the proper tools.
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K3NRX
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« Reply #12 on: June 07, 2012, 06:07:26 PM »

Under no circumstance do I want this thing flying off the car.....

V
KA3NRX




Before I got a lesson in why you drill a hole, I used a triple magmount. With two magnets forward and one to the rear it was fine with a Little Tarheel II with a 60" whip extended quite far on 80m driving at 70MPH into a headwind.

The 3 magnets are bolted on to an aluminum triangle...my deliema is that the magnets are spaced apart far enough that it does not fit on the boot, no thanks to the spoiler.....by drilling three holes no more than 5 inches inward from the origional holes at the tip of the triangle, I think I can move the magnets in far enought where the whole mount can fit on the trunk without going over the end at the rear windshield, or over the spoiler.....That is why (and where) I would drlll holes.....

V
KA3NRX

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W4FID
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« Reply #13 on: June 08, 2012, 04:47:31 AM »

The entire surface of all the magnets MUST be in solid -- flat -- good contact with the surface for two reasons.

FIRST if the wind gets under an edge or the antenna hits a tree and "pries" the mount loose you will be amazed at how strong the coax is as the mount and what's left of the antenna smack the hell out of your car. The coax will not finally break or you will not get the car stopped quickly enough to avoid significant damage and what's left of the antenna and mount will be in the middle of the road as a hazard to everyone else.

SECOND the antenna is a vertical which is capacity coupled to the car which is capacity coupled to the earth. The magnets are plates of a capacitor and the paint is the dialectric and the car body is the other plate. The car body is a plate of a capacitor and the tires are the dialectric and the earth is the other plate. Capacity for coupling is highly dependent on surface area -- larger capacitor plates have more capacity and provide better coupling. That's why on 2M a smaller magnet is OK -- strong enough for a small antenna and the higher frequency couples with less capacity. But for HF you need all you can possibly get and mag mounts at best are marginal -- mechanical electrical connection to the car's body is much better.
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K3NRX
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« Reply #14 on: June 11, 2012, 04:55:21 AM »

OK...my friend with the machine shop drill press poked a few holes into the triangle, and the magnets are closer in together (with enough give to connect the coax).....and it now fits the G6 trunk.....Looks like this thing will work out....now if only 10 meters would open!!!!!!!...... Roll Eyes..............

V
KA3NRX
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