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Author Topic: OK...who here uses a tri-magnet mount????.....  (Read 15241 times)
K3NRX
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« on: July 26, 2012, 04:47:49 AM »

...on the trunk of their car.....not on a flat bed of a pick up, but on the trunk of their car.....I am looking to see how well it holds at high speeds (no faster than 70 mph).....The antenna is a 10 meter workman hamstick whip, so it's rather long and light.....give me an idea as to it's performance regarding hold at high speed.....I don't want what happened to me last fall to happen again.....(the hamstick on a single magnet mount coming off the trunk while on the highway--fortuneately, no one was around me at the time)......

V
KA3NRX

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W5DXP
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« Reply #1 on: July 26, 2012, 06:28:04 AM »

I use a tri-mag with a 17m hamstick on the cab of my pickup - works fine. Put two magnets in the direction of the front of the vehicle.
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K3NRX
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« Reply #2 on: July 26, 2012, 01:19:30 PM »

I use a tri-mag with a 17m hamstick on the cab of my pickup - works fine. Put two magnets in the direction of the front of the vehicle.

When you say on the cab, I presume you mean the roof and not the hood.....So it's held on tight at moderately high speeds, eh??....No worries, I presume.....

V
KA3NRX

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N6AJR
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« Reply #3 on: July 26, 2012, 08:03:14 PM »

Just had a friend using one on his pickup roof, and he made it all the way from sacramento to lL.A. and about half way back and then it blew off.... dont trust them for anything bigger than a 3 or 4 foot tall ham stick and then run a guy ( fishing line or fine rope) towards the front of the vehicle to hold back against the breeze.
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W4FID
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« Reply #4 on: July 27, 2012, 04:46:48 AM »

I have the tri (the one with 3 magnets about 5" diameter each) in the middle of the roof of my F-150. The hamsticks that are about 7 ft so they hit a LOT of stuff (about 13'-6 to the tip) so I have a spring then a quick disconnect male. Each band's whip has the female quick disconnect. Been doing it that way for about 10 years. Lots of Interstate trips. Cross winds, 85 MPH, turbulence from semis, country roads, construction zones, no problems. Do buy a good quality one with strong magnets. Do wax the roof a few coats before you place the mount. Do have enough "muscle" or leverage to lift a corner and get your fingers under it then lift it up when you take it off (usually I have someone on the other side of the truck to help me). If you slide it the roof will get scratched.

Remember the mount not only has to hold the antenna physically --- it is the capacitor plate for capacity coupling to the vehicle for the "ground plane" part of the antenna system. The larger diameter the magnets the better they hold and the more coupling surface area you have. The wider spaced the magnets are the better they hold and the more coupling surface area you have. This is more of a factor at lower frequencies like 40M that at 2M but is a factor for all operation. Poor ground plane means poor radiation efficiency.

I destroy a hamstick occasionally and I have to stand in the doorway with my foot on the arm rest to stretch out enough to reach the base of the whip to change it. Both are not good features. But centered on the vehicle helps the radiation pattern be more symmetrical is good. Above the sheet metal from my and nearby vehicles , guard rails, is good. So you look at the pros and cons and choose what you like.
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K1CJS
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« Reply #5 on: July 27, 2012, 05:42:18 AM »

Mag mounts are good for antennas like that--if you're at a standstill or travelling slowly.  Consider this:  You specified at speeds of 70 MPH or less.  Any sort of wind gust in the opposite direction pushes that to way over 70 MPH.  If you've got a large antenna on that mount, you're asking for problems, either the complete failure of the ability of the mount to hang onto the sheet metal or a limited failure resulting in slippage--and the possible ruining of the vehicle paint finish.

If you insist on travelling that fast, you should consider having some sort of two direction lanyard attached to the magmount and to the vehicle ahead of where the magmount is on the vehicle to prevent accidental holding failure and the resulting damage that that may cause, up to and including if the magmount fails, flying off and possibly ruining your antenna or--in a worst case scenario--hitting another vehicle and damaging it, or possibly killing somebody.  IT CAN HAPPEN.
« Last Edit: July 27, 2012, 05:44:46 AM by K1CJS » Logged
WA4HBK
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« Reply #6 on: July 27, 2012, 06:44:35 PM »

Don't know how well they would hold up under long term use, but can attest they can do a job on your finger if it gets between the magnet and the roof.
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KE9PP
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« Reply #7 on: July 31, 2012, 12:40:13 PM »

Please don't forget that in an accident they WILL come off and become a potentially deadly projectile and your insurance company may or may not cover you for harm done to others!  You may be personally liable for any death or damages, think "involuntary manslaughter!"
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M6GOM
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« Reply #8 on: August 01, 2012, 05:06:53 AM »

I used one with a Little Tarheel II with 6ft whip no problem at over 70MPH into very strong headwinds.

Whilst it stayed on, that was the only thing it did. The RF ground was abysmal. TX on 80m with 50W would result in my TS480 rebooting, so high was the common mode.
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W5DXP
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« Reply #9 on: August 01, 2012, 06:51:06 AM »

The RF ground was abysmal.

When one takes the time to measure the tri-mag capacitance, one will most likely find an inadequate RF ground below 14 MHz. I don't remember my exact measurements but I remember 40m being questionable and 80m being inadequate.
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K1CJS
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« Reply #10 on: August 01, 2012, 08:52:46 AM »

When one takes the time to measure the tri-mag capacitance, one will most likely find an inadequate RF ground below 14 MHz. I don't remember my exact measurements but I remember 40m being questionable and 80m being inadequate.

For anything over 6 meters, the average vehicle does not provide a sufficient ground plane.  That is why HF mobile is such a challenge.
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KD5TXX
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« Reply #11 on: August 04, 2012, 08:21:50 PM »

I use a single mag mount and have never had one come off.  60k + a year and been doing it for 10 years.  I know there are better options but this works for me.  40-10 m.
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W9MMS
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« Reply #12 on: August 05, 2012, 08:21:11 AM »

>>> ..I don't want what happened to me last fall to happen again.....(the hamstick on a single magnet mount coming off the trunk while on the highway--fortuneately, no one was around me at the time)...... <<<

Are you willing to KILL or Disfigure  somebody, simply because you don't want to Drill a hole in your PRECIOUS Car?
Does running a Dummy Load worth the Risk?

http://www.k0bg.com/antmount.html

Scroll down to " Mag Mounts"

http://www.k0bg.com/eff.html

Just my $0.02 worth.


(((73))) Milverton.

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W8JX
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« Reply #13 on: August 05, 2012, 09:19:23 AM »

Are you willing to KILL or Disfigure  somebody, simply because you don't want to Drill a hole in your PRECIOUS Car?

I see we are back to the magic "Flying Antenna" personal injury claim/theory that has NEVER been documented to have happened. I have used custom built double 5 in mag mount for many years designed to fit between the stiffeners on my roof at time with a ham stick and have never lost one or come close to it.
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You can embrace new computer/tablet technology and change with it or cling to old fall far behind....
KD0PBO
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Posts: 67




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« Reply #14 on: August 05, 2012, 07:27:43 PM »

Been using a mag mount 5/8 2m antenna for almost a year now and still occasionally switch it out for a Wilson 1000 mag mount (cb for the farm, shoot me if you don't approve  Tongue ). Have NEVER had an issue with the 2m in the year I've had it and the Wilson in the ~4 years I've had it. Been rear ended twice, first with the Wilson and second with the 2m. Thankfully, neither accident was bad enough to wreck my truck but man, they still hurt. Checked the antennas after both accidents and they hadn't moved at all. Maybe the whole magnetism thing really DOES work!  Shocked

In all seriousness, I've never had an issue with mag mounts falling off because I was driving down the highway. Never been in a serious enough accident to have them turn into a missile. (Maybe, Mythbuster's should test this ham radio legend.) Honestly, the way I think about it, the number of years CB radios have been popular and people have used mag mount antennas like Wilsons for their CBs, you would think we would have heard about the "flying antenna of death" by now. So either it is an extremely rare occurrence or it just doesn't happen at all.

Take it for what it's worth.
73
Miles D.     
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