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eHam Forums => Mobile Ham => Topic started by: K3NRX on November 13, 2011, 02:09:54 PM



Title: Magnet Mounts....Just how safe are they????
Post by: K3NRX on November 13, 2011, 02:09:54 PM

....when using a Workman Hamstick that is pretty long???....I was on the highway today and the damn thing blew off while doing about 60-65 mph.....fortuneately no one was behind me......had to pull over and dismantle the whole thing and throw it in the trunk....I am now hesitant to use this operation at relatively high speeds, and it's quite unnervng to me.....anyone have any ideas as to how I can make this safer and still use the magnet mount???.....Should I get a trunk lip mount or something for a hamstick this long???.....

V
KA3NRX



Title: RE: Magnet Mounts....Just how safe are they????
Post by: K0BG on November 13, 2011, 02:38:59 PM
Ask 100 people who have them, and half will say they've come off, the other half say will say no. And, it doesn't make too much difference how many magnets they have. They just get heavier, and do more damage when they do come off.

According to the NHTSA, there has been one fatality, and less than 50 reported injuries caused by flying mag mounts. Note the work reported! I have a friend over in Texas, who has lost one 2 meter mag mount, and two coils off his old Hustler HF antenna, and he doesn't know when they came off. There were there when he left, but not there when he got to where he was going. Makes you wonder just how often this happens.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K3GM on November 13, 2011, 06:31:31 PM
A couple of years ago, I put a temporary 6m Hamstick on the roof of my new Tahoe to work some weak signal springtime Es on while I was doing some traveling.  My two permanent NMO roof mounts were both filled with FM antennas, so I put the Hamstick on a Larsen mag mount.  The damn thing blew off the roof of the Tahoe at 70mph, startled the crap out of me, and ended up stuck to the side of the rear quarter panel poking out sideways into the adjacent lane of the New Jersey Turnpike. I got the EL58 I was looking for, but ended up with a nice scuff on the side of the  truck for my effort. No more mag mounts.....


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K5LXP on November 13, 2011, 06:55:41 PM
Yeah, unless you happen to be working the rig you may not notice it when it departs.  I lost one off my service van once, when I got there all I had was a frayed coax dragging behind.  Odds are they'll just bounce and skid on the road for a ways and that's the end of it, but you always wonder. 

I use a mag mount for my portable APRS and have personally witnessed it blow off from the gust of a truck going the other way on the highway.  Fortunately it was on a "short leash" of coax coming out of the trunk and it didn't get far, but it showed me that even a 2M quarter wave is enough profile to get plucked off in the right circumstances.

Mark K5LXP
Albuquerque, NM


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KD5TXX on November 13, 2011, 07:20:55 PM
I have used Mag mounts (5" type) for 10 years and never lost one.  And I drive 50-60K a year.  With a small 3" mag, I have had them fall.  I now only use a 5" mag mount and use 40m-10m whips.  I use the mini ones, so that may be why they don't fall.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 13, 2011, 07:40:21 PM
Ask 100 people who have them, and half will say they've come off, the other half say will say no. And, it doesn't make too much difference how many magnets they have. They just get heavier, and do more damage when they do come off.

Simply not true. Yes as stated above with proper magnet size there will be no problem. In 25 plus years of using them I have only lost one and that was doing 70 mph west bound up Bozeman pass with 60+mph head winds. (a 4 inch one) The only weakness of one is size of magnet for antenna in use. Some vendors cut corners here to cut costs.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K1CJS on November 14, 2011, 05:38:36 AM
It really doesn't make much difference what kind of magmount you have, a single magnet base, a three magnet base, or what guarantees there are about that particular magmount.  Magmounts should not be used at highway speeds, period.  And especially not for heavier antennas, no matter how much the manufacturer says that they'll hold up.  If you don't have the thing fly off and cause damage elsewhere, you're going to have damage done to your vehicle.

A friend used a three magnet base magmount antenna--because the guarantee was that it would not come off.  Well, it didn't come off--but it did leave some beautiful scrapes along the roof of his SUV as it slid backwards during a long road trip.

Use what you want to use, but just remember, you'll pay one way or the other--either for a good, quality mount or for the damages that a cheap mount will cause.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 14, 2011, 05:56:53 AM
It really doesn't make much difference what kind of magmount you have, a single magnet base, a three magnet base, or what guarantees there are about that particular magmount.  Magmounts should not be used at highway speeds, period.  And especially not for heavier antennas, no matter how much the manufacturer says that they'll hold up.  If you don't have the thing fly off and cause damage elsewhere, you're going to have damage done to your vehicle.

Again simply not true. With PROPERLY side magnet it will not come off at highway speed. Tee only thing I will use a 3 inch mag for is a 1/4 wave 2m vertical. It has NEVER failed at this is 10 of thousands of miles. For a 5/8 wave 2 meter I use a 4 inch and it has never failed except for bozemen pass once which was my fault not mounts. (place is well know for wind gusts well exceeding 100mph often with frontal passages) Package deals that include a antenna rarely have a big enough magnet to securely hold it. I always get magnet separately to insure it is properly sized.  I have held a 8 foot hamstick on roof of a suburban at highways speed many times using  custom mag mount with two 5 inch magnets.

Again simply put, use correctly sized magnet and you will have no problems

A friend used a three magnet base magmount antenna--because the guarantee was that it would not come off.  Well, it didn't come off--but it did leave some beautiful scrapes along the roof of his SUV as it slid backwards during a long road trip.

Some guarantees are not worth paper they are written on. If mag was sized properly, it would not have walked down roof. Once again it is ALL about the size of the magnet vs antenna in use.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K0BG on November 14, 2011, 06:05:06 AM
I just love how positively certain you are John. The reason you're so adamant is because you use one, and never had a problem. Consider yourself lucky, and let's hope you didn't speak to soon!

As I alluded to, there is a lot about mag mounts to love, and hate. But ignoring one, in favor of another isn't the tact to take. Just ask Joe Paterno.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 14, 2011, 07:23:52 AM
I just love how positively certain you are John. The reason you're so adamant is because you use one, and never had a problem. Consider yourself lucky, and let's hope you didn't speak to soon!


Alan I speak from many many years of experience with this. A mag mount is only as good as the magnet it uses. There is flux density (pull/holding power per square inch) and its diameter. The two play a critical role is countering the leverage applied to magnetic base but antenna load for momentum and wind loading. The large diameter magnet not only increases raw holding power (ie more square inches of surface area) but it also increases the amount of "leverage" needed to unseat it due to not only increased holding power but also due to extended contact radius relative to antenna center. Actually Alan even if you took two magnet mounts made of same material and made one 5 inches and other 4 inches outer diameter but deliberately kept square surface area the same by making center hole larger.  The 5in one will have same dead weight lifting/holding power but will better resist be unseated by torque loads on mount placed there by antenna due to increased radius relative to antenna center.

I do not consider myself "lucky" at all but rather it is because of knowledge and simple logic that I have had no problems. I worked in flight test R&D for many years and learn that everything that fails does so for a reason and you modify design to get desired results. In this case bigger magnets will work when PROPERLY sized for antenna in use. Package deals rarely have correct mag size as they are looking to make max possible profit and minimize shipping costs in large volumes by keeping weight light

Now if you cannot wrap you head around this concept then it is you relying on luck not me.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K6JRS on November 14, 2011, 09:08:07 AM
I guess I've been one of the lucky ones. I recently installed a permanent NMO mount for VHF/UHF operations. Before that I put over 250,000 miles, well over 50% at freeway speeds, on a 3-4" mag mount. I think ti was a Diamond mount because I was using one of their longer VHF/UHF whips. This mag mount was used on two different vehicles over it's lifetime.

I should buy a lottery ticket...

73,
Jay  K6JRS


Title: RE: Magnet Mounts....Just how safe are they????
Post by: M6GOM on November 14, 2011, 09:20:01 AM
I have never used anything smaller than a 5" magmount so have never had anything fall off. I used a 5" magmount with CB antennas without incidence for nearly 20 years, covering in excess of 100,000 miles per year with several years in excess of 150,000 miles a year in all conditions. I used a Little Tarheel II with 60" whip with a triple magmount and did 80+MPH into headwinds again with no incident.

Nowadays I drill holes but sometimes when vehicle hopping, I'll still use a 5" magmount with a dualbander. I wouldn't use a hamstick with a single magmount and if I were to ever use a 3" mag, I'd not want anything more than a 1/4 wave 2m whip on it.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W2RI on November 14, 2011, 10:07:24 AM
They can and do come off. When I first started mobiling, I had a triple magnet mount for a 20M hamstick. The thing came off on a parkway; I couldn't have been doing more than 70mph. Now I won't use one unless it's bolted down.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 14, 2011, 04:58:53 PM
They can and do come off. When I first started mobiling, I had a triple magnet mount for a 20M hamstick. The thing came off on a parkway; I couldn't have been doing more than 70mph. Now I won't use one unless it's bolted down.

There is no way a triple 5 inch magnet should come loose unless surface was either not flat or metal was so thin that it oil canned and flexed under load and broke contact area. I have a custom made mount with two 5 inch ones that has held a 20 meter ham stick at 70+ and has also held a full sized hustler 2m collinear under same conditions. (once with 20m stick I went under a lower overhang and took out some lights with it by accident and antenna did not come loose)  It is on a nice flat part of a sturdy roof with stamped stiffeners in it too. You can not place magnets on a weak or curved roof and expect it to hold under high torque load.









Title: RE: Magnet Mounts....Just how safe are they????
Post by: WB2WIK on November 14, 2011, 06:10:04 PM
I just think of why "mag mounts" were invented, which is for temporary operations.

I've also measured performance of many mag mounts over the years, and found that on UHF they're actually pretty good.  On VHF, a bit less good.  On HF, not very good at all; they're just not sufficient capcacitance through the magnets and paint to create any kind of low loss system for grounding.  40-50 pF won't cut it.  Frankly, 1000 pF won't do it.  10,000 pF would probably be okay for a 50 Ohm antenna, but you can't get that with 1-2-3-4 magnets, it's just not going to happen.   Impossible.

A friend of mine in Florida sent me a "Firestik" mag mount he was using.  I measured it.  Its efficiency was horrendous, but then I made some more measurements to find out why: They were relying on the magnet to be a conductor.  It wasn't.  The resistance from the coaxial feedline outer conductor to the magnet was thousands of Ohms, since magnets are not good conductors.  So, in all cases, it was half an antenna.

I modified it to add copper foil from the feedline to below the magnet, and just epoxied that in place.  Efficiency increased from 9% to about 50% with this simple modification which took ten seconds.





Title: RE: Magnet Mounts....Just how safe are they????
Post by: KC7YRA on November 14, 2011, 06:26:11 PM
There is no way a triple 5 inch magnet should come loose unless surface was either not flat or metal was so thin that it oil canned and flexed under load and broke contact area.

I have had mixed results.  I once traveled many thousands of miles 1 summer with my folks.  As a way to shut me up, the let me stick a 20 meter hamstick to the roof with a 3 magnet mount.  It worked fine.

But several years later, I had it on my truck along with several other magmounts (5).  Doing 80mph down the interstate into a significant headwind (as we ALWAYS have here in Wyoming), A tractor/trailer passed me and blew every single magmount off the roof.  I mean EVERY.  I also had it get to oscillating while offroading and tip over a number of times.

So I am 50/50.  I have had extremely mixed results.  I now drill all my antennas.  But at the same time, I'd use a magnet mount for temporary stuff.

Brad 


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 14, 2011, 09:09:02 PM
I've also measured performance of many mag mounts over the years, and found that on UHF they're actually pretty good.  On VHF, a bit less good.  On HF, not very good at all; they're just not sufficient capcacitance through the magnets and paint to create any kind of low loss system for grounding.  40-50 pF won't cut it.  Frankly, 1000 pF won't do it.  10,000 pF would probably be okay for a 50 Ohm antenna, but you can't get that with 1-2-3-4 magnets, it's just not going to happen.   Impossible.

It would be interesting to actually measure capacitance.  I have had good results with double mag on roof.


I modified it to add copper foil from the feedline to below the magnet, and just epoxied that in place.  Efficiency increased from 9% to about 50% with this simple modification which took ten seconds.

I think this a stretch as most mobile HF antennas are basically radiating dummy loads. (negative gain antennas)


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KD0PBO on November 20, 2011, 12:40:29 PM
I would drill holes for my antennas but seeing that i mostly operate while offroading i'd rather have the magmounts get knock off and leave some scratches than have a NMO mount rip a hole in the roof of my truck...just my $.02 if its even worth that

Miles


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 20, 2011, 03:35:53 PM
There is no way a triple 5 inch magnet should come loose unless surface was either not flat or metal was so thin that it oil canned and flexed under load and broke contact area.

I have had mixed results.  I once traveled many thousands of miles 1 summer with my folks.  As a way to shut me up, the let me stick a 20 meter hamstick to the roof with a 3 magnet mount.  It worked fine.

But several years later, I had it on my truck along with several other magmounts (5).  Doing 80mph down the interstate into a significant headwind (as we ALWAYS have here in Wyoming), A tractor/trailer passed me and blew every single magmount off the roof.  I mean EVERY.  I also had it get to oscillating while offroading and tip over a number of times.

So I am 50/50.  I have had extremely mixed results.  I now drill all my antennas.  But at the same time, I'd use a magnet mount for temporary stuff.

Brad 

Problem with drilling is that sheet metal is thinner than ever and a hole mount does not provide holding power it once did. Any wind load heavy enough to unseat a 3 mag mount with 5 inch magnets will put a LOT of strain on hole mount and bend metal and likely pull out over time unless hole is gusseted. Most car makers use as thin of metal as possible to limit cots and maximize profit.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KC7YRA on November 20, 2011, 04:55:11 PM
Well, I managed to put a 5 inch HI-q screwdriver, totaling 14 feet tall, on my truck with a single mounting point.  And it stays on at 90mph.

And this is on a Tundra with the thinnest sheet metal In the industry.

Brad


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 20, 2011, 05:07:05 PM
Well, I managed to put a 5 inch HI-q screwdriver, totaling 14 feet tall, on my truck with a single mounting point.  And it stays on at 90mph.

And this is on a Tundra with the thinnest sheet metal In the industry.

Brad

I do not think Toyota has thinnest metal in a truck. That honor likely goes to Detroit.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K0BG on November 21, 2011, 07:48:16 AM
The holding power of a mag amount is also based on the thickness of the material it is stuck to. And by all accounts, it is getting thinner as automobile manufacturers strive to meet the new fuel economy standards. Adding some insult, Audi, and MB both use lamented "sheet metal", that is actually aluminum or steel sandwiched together with rubber. A mag mount won't stick even on the steel variety. Oh! And how about the 2012 Ford Mustang? Composite hood, trunk lid, fenders, and lower body. That leaves the top, and it's 18 ga.


PS: For you Ford lovers, the 2012 Cobra Super Snake has 750 HP, and a top end of over 200 mph. It goes to 0 to 100 faster than a Vette can get to 60!


Title: RE: Magnet Mounts....Just how safe are they????
Post by: AC4RD on November 22, 2011, 04:18:14 AM
The holding power of a mag amount is also based on the thickness of the material it is stuck to. And by all accounts, it is getting thinner as automobile manufacturers strive to meet the new fuel economy standards. Adding some insult, Audi, and MB both use lamented "sheet metal", that is actually aluminum or steel sandwiched together with rubber.

Yesterday on the highway, I saw one of those big crew-cab pickups with the dual rear wheels, enormous thing ... and the big protruding rear fender was cracked and broken, with pieces missing.  That fender, to my surprise, was *plastic* of some kind.   :-(


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 23, 2011, 09:35:23 AM
Yesterday on the highway, I saw one of those big crew-cab pickups with the dual rear wheels, enormous thing ... and the big protruding rear fender was cracked and broken, with pieces missing.  That fender, to my surprise, was *plastic* of some kind.   :-(

No surprise here. It obviously must cost less than metal and anything to save a buck on build costs. Personally I have always though these dually pick ups a bit silly.  Unlike really dual wheel trucks that narrow track of inner tires to limit rear axle width, with dual pick ups they just basically slap another wheel on it with a plastic fender and let it all hang out. Cheaper to do that way.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: AA4HA on November 24, 2011, 01:18:03 PM
I have three antennas mounted on an MB. I did not drill for any of the antennas nor did I use magnetic mounts. They are lip mount antennas at two corners of the rear trunk lid (by the tail lights) and the third in the center (right in front of that auxiliary brake light. I am changing out two of the antennas for a quad band (10,6,2 and 70 cm) in the prime position and a shortie 1/4 wave whip for APRS at one of the trunk corners.

The car is a nightmare to put antennas on as it has them hidden all over the bodywork, front and back deckwork (dashboard) and under the bumper covers (cell antennas and TELEAID antennas hidden under there). I do not want to drill holes and my big sacrifice was to find an open weatherproof grommet to get from the battery lid to where the FT-8900 is screwed down to the floor under the front seat. They thoughtfully put an air conditioning vent beneath the driver and passenger seats so the rear seat passengers do not get sweaty toes.

I bought a few spray cans of onyx black paint so the antenna bases are all painted the same color as the car. I have not encountered any alloyed metal on the car that would be paramagnetic. Either it has been solid steel or that plastic/rubber stuff on bumpers and some trim pieces.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: AB4D on November 25, 2011, 06:47:58 AM
I've learned over the years, it is just better to drill the hole than to use magnet mounts.  If you use a magnet mount, I can almost guarantee it will scratch up the paint on the surface.  I've yet to see where it hasn't.  I've traded in vehicles with residual antenna holes that I plugged with rubber plugs or installed a cell phone antenna, and I've never heard a word mentioned about them.  I once traded in vehicle with scratches from a mag mount, they dropped the value $500 to allegedly repaint the roof.

For me, the safety factor is why I will not use a magnet mount.  Why take a chance of one coming off?  Likely, probably not, impossible, don't bet your life on it.  To me, it's just not worth the risk.  What if it comes off and launches into the windshield of a car behind you?  Or you accidentally hit another vehicle and it flies off hitting a pedestrian  What if it causes a fatal wreck on a highway? Think about these possible situations where you would be held liable.  I just don't believe it's worth the risk.  Drill the hole or take it to an installer for a much safer antenna install.  

Performance wise, I have not performed any research or tests that suggests which mounting method works better.  However, common sense suggests that a directly coupled antenna vs. one that is magnetically coupled, probably should work better, all else being equal (mounting location, etc).

I can also attest to the quality of the metal on the Toyota Tundra, very thin.  I am not sure if it's the thinnest, but it has to be close. The truck bed quarter panels are so thin, Toyota factory installed pieces of dynamat type material on the inside of the panel to help control noise and vibration. I did the same thing to the roof (second skin damplifier) and also had to attach a pair of three foot long steel rods to the underside of the roof to help stabilize the sheet metal.

73


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 26, 2011, 06:22:32 AM
I can also attest to the quality of the metal on the Toyota Tundra, very thin.  I am not sure if it's the thinnest, but it has to be close. The truck bed quarter panels are so thin, Toyota factory installed pieces of dynamat type material on the inside of the panel to help control noise and vibration. I did the same thing to the roof (second skin damplifier) and also had to attach a pair of three foot long steel rods to the underside of the roof to help stabilize the sheet metal.

I doubt rods in roof are the because thin sheet metal. It is likely for crash protection and part of a total design. They go to great lengths to do well in crashes and roll overs and no longer depend solely on sheet metal. Also they use a LOT of sound deadening material in cars these day and it adds weights so the try to recoup that with thinner metal on some area. I was in a serious wreck in a Toyota car many years ago and walked away for it because car held together well. Even though front end was heavily damage and pushed in the "cockpit" was intact and all 4 doors opened and closed fine and were still aligned. This was because Toyota braced body well for side and front impacts. I have little doubt that had I been on a US car of similar size I would have fared much worse. 


Title: RE: Magnet Mounts....Just how safe are they????
Post by: AB4D on November 26, 2011, 11:01:58 AM
I can also attest to the quality of the metal on the Toyota Tundra, very thin.  I am not sure if it's the thinnest, but it has to be close. The truck bed quarter panels are so thin, Toyota factory installed pieces of dynamat type material on the inside of the panel to help control noise and vibration. I did the same thing to the roof (second skin damplifier) and also had to attach a pair of three foot long steel rods to the underside of the roof to help stabilize the sheet metal.

I doubt rods in roof are the because thin sheet metal. It is likely for crash protection and part of a total design. They go to great lengths to do well in crashes and roll overs and no longer depend solely on sheet metal. Also they use a LOT of sound deadening material in cars these day and it adds weights so the try to recoup that with thinner metal on some area. I was in a serious wreck in a Toyota car many years ago and walked away for it because car held together well. Even though front end was heavily damage and pushed in the "cockpit" was intact and all 4 doors opened and closed fine and were still aligned. This was because Toyota braced body well for side and front impacts. I have little doubt that had I been on a US car of similar size I would have fared much worse. 
v

The rods ARE there because I installed them myself, they are not factory installed.  As factory manufactured, the roof sheet metal is very thin by earlier standards, and is unsupported, except for a lateral support made from stamped steel that runs side to side, mid cab.  If you were to look at a few of the Toyota Tundra forums on the net, you will find complaints about the "new" Tundra regarding thin sheet metal and a noisy interior.  A lot of folks recommend sound deadening in the Tundra, as I do, the noise reduction in the interior is substantial.

73, Jim.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on November 26, 2011, 11:28:59 AM

The rods ARE there because I installed them myself, they are not factory installed.  As factory manufactured, the roof sheet metal is very thin by earlier standards, and is unsupported, except for a lateral support made from stamped steel that runs side to side, mid cab.  If you were to look at a few of the Toyota Tundra forums on the net, you will find complaints about the "new" Tundra regarding thin sheet metal and a noisy interior.  A lot of folks recommend sound deadening in the Tundra, as I do, the noise reduction in the interior is substantial.

73, Jim.

I stand corrected on this matter. I think I would have tied adding another layer of metal beneath roof to stiffen it rather than rods. I could be reverse curved somewhat to preload and stiffen roof when metal is secured and bonded into place. You have helped a lot for a roof mount antenna. I still would buy a Tundra though if they made a 3/4 ton.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K2OWK on November 26, 2011, 03:04:05 PM
I have an Laird magmount. I use a dual band 2 M/ 70 CM antenna. Never had it fall off at any speed. In fact the magnet is so strong it is hard to get it off when you want to. I attached a piece of thin felt to the bottom to prevent scratching (no it does not interfear with the ground plane coupling to the car). I have used mag mounts for 50 years and have never had one fall off. I always buy the best magmounts available. I do not purchase the cheepies. Buy a good quality mount and you will not have any problems. Some of the new rare earth magnets are so strong it is hard to remove them, but they are not cheep.

Just my opinion.

73s

K2OWK


Title: RE: Magnet Mounts....Just how safe are they????
Post by: N6AJR on December 07, 2011, 11:04:03 AM
Another trick you can do is pick up a spare rear trunk lid that matches your car, and drill and mount as many antennas as will fit on the lid.  when you sell the car, put the "real" trunk lid back on.

Bye the way, if you use a trunk lip mount ( like the diamond  K 400 C) it needs to go on the "sides" of the trunk lip, not the back near the rear window. These are strong mounts  when mounted with the load sideways, but when mounted on the back of the trunk lid they will bend the lip.  they are made to go on the side.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: AE6ZW on December 07, 2011, 10:36:13 PM
I use 5 inch magnetic mount ( MFJ or High Sierra antenna ) , they seems to hold 5/8 wave 2 meter ANT  much better than smaller magnetic mount, which it came with 5/8 2 mtr antenna.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KB2FCV on December 08, 2011, 10:02:50 PM
I haven't used a mag mount for well over a decade, I drill mine. The last two cars I've had I drilled them the day I picked them up from the dealer.

Sure, some mag mounts might hold ok when driving but what happens if you're involved in an accident and that mag mount is suddenly now a missile?


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 09, 2011, 12:43:22 PM
Sure, some mag mounts might hold ok when driving but what happens if you're involved in an accident and that mag mount is suddenly now a missile?

If you get in that big of a wreck the antenna is the least of your worries.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: AI4HO on December 11, 2011, 05:50:31 PM
I have used and will continue to use mag mounts when and where I think appropriate.  I used to use nothing but mag mounts..big small, 1- 5" magnet or 4- 5" magnets, didn't make any difference.  Since I bought my 2011 Toyota Tundra, 4X4 double cab, I have not used any until about a month ago.  My lip mount that I had on the hood of my truck is without an antenna.  Until I can get another antenna I have a dual band mag mount on the roof as a temporary setup until I find an appropriate antenna for my truck.  I have my Tar Heel HP-40 now mounted in the bed of my truck, where as when I had my 09 Ranger, it wasn't the case.  Being as I had a cap over the bed, and effectively negating the bed as a source to mount my Tar Heel.  I had already had a big 4 magnet mount I bought from Robert at Tar Heel, he had produced several of these huge mounts made for the HP-40A, and the "Stubby" Tar Heel antenna.  I mounted this beast on the roof of my truck..well back, and within inches of the roof of the cap covering the bed.  This system worked well for the entire 2 and a half years I had my Ranger. 

Never once, did I ever have one of my mag mounts "fly" off, I have seen them come off from friends who had mag mounts on their vehicles.  Once, while riding with a friend who has mag mounts we were going at a pretty decent clip, he hit the breaks for a light that changed..really fast, I wound up with a bunch of coax and this mag mount with the antenna attached almost in my lap.  Once stopped, we pulled off, I got out to see why this mount came off so easily, I visually inspected everything on and around this mount.  Found some moisture under the mount, and on the roof, wiped all parts down, made sure there was NO moisture on or under this mount.  We then proceeded onward to our destination without further incident.  Moisture is definitely not a good thing for a mag mount, if any gets in under around a mag mount, it can definitely turn that mild mannered mag mount into a ballistic missile.  I would check my mounts on a weekly basis, making sure there was no moisture, grit, anything that could cause that magnet to loose contact with the surface under it.  I also used magnet covers, or whatever they are called, it covers the magnets bottom, usually has the center cut out..looks sorta like a donut. This protects the vehicles roof surface from scratches and what not, if you're using a mag mount these are a life saver for your vehicle.

I believe, that if one properly places the mag mount checks to make sure  that there is no moisture, or grit anywhere on or under the magnet.  I had been in 2 or 3 accidents..none of which were my fault.  Two were in the area of my kids high school, and I was traveling at less than 20 MPH, the other one..an elderly gentleman pulled in front of my Ford Sport Trac when I had it.  I was traveling at 45 MPH, guy pulls slap in front of me..I had zero time to evade this car and T boned his 90-91 Plymouth, with my 03 Sport Trac, my big 4 magnet mount I had at the time slid forward an inch, maybe an inch and a half, the edges of the mount scratched a bit of the paint on the roof, but the mount held firm.  I think mag mounts serve a purpose, there are time when nothing but a mag mount will do, these days, my use of mag mounts are limited only by circumstances.  I will use them again, no doubt, but for now, my little dual band mag mount is all I need at present.  I still have my big 4 magnet mount I bought for my Tar Heel HP-40A, haven't decided weather or not to sell it, as it is still usable, just needs a good cleaning and lube the bolts the magnets are attached, use my wire wheel, get rid of a little rust build up and it is good to go. 

Any way..thank you all very much for taking the time to read my post, Merry Christmas to one and all who celebrate this joyous time of year.  May y'all get what ya want, want what ya get, I pray that 2012 is a Happy, healthy,but above all a safe New Year.

73 de Mark
W3LZK


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K1CJS on December 15, 2011, 09:08:29 PM
...If you use a magnet mount, I can almost guarantee it will scratch up the paint on the surface.  I've yet to see where it hasn't.  I've traded in vehicles with residual antenna holes that I plugged with rubber plugs or installed a cell phone antenna, and I've never heard a word mentioned about them.  I once traded in vehicle with scratches from a mag mount, they dropped the value $500 to allegedly repaint the roof.

For me, the safety factor is why I will not use a magnet mount...  

That last line says it all.  The safety factor should be the one thing that would preclude the use of magnet mounts on a moving vehicle.  No matter how many miles someone claims to have travelled with no issues, there is always tomorrow.  And tomorrow may well prove to be the day that something DOES happen--even to someone who thinks they're safe because nothing ever happened to them.

I can also attest to the paint issues that are mentioned in the first paragraph.  I had the use of a company car where I used a magmount, and I had to get it repaired where the magmount had damaged the paint--or I had to pay up front when turning it in. 

Magmounts certainly are convenient--but is that convenience worth someones life?  I think not.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KX5F on December 16, 2011, 05:45:12 AM
Went to a Hamfest last month and my brother-in-law was following in his car, I loaned him a 1/4 wave and a brand new Larsen mag-mount so we could talk back and forth on the trip.   Everything worked fine until we got back and he went to remove the mag-mount,  the whole thing came apart from the magnet, just broke, and this was a Brand New Larsen mag-mount.  It was a good thing it was only a 1/4 wave Larsen antenna, as anything larger would have been lost.   Lost my trust in mag-mounts after that.      Patrick   kx5f


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 16, 2011, 06:20:36 AM
...If you use a magnet mount, I can almost guarantee it will scratch up the paint on the surface.  I've yet to see where it hasn't.  I've traded in vehicles with residual antenna holes that I plugged with rubber plugs or installed a cell phone antenna, and I've never heard a word mentioned about them.  I once traded in vehicle with scratches from a mag mount, they dropped the value $500 to allegedly repaint the roof.

For me, the safety factor is why I will not use a magnet mount...  

That last line says it all.  The safety factor should be the one thing that would preclude the use of magnet mounts on a moving vehicle.  No matter how many miles someone claims to have travelled with no issues, there is always tomorrow.  And tomorrow may well prove to be the day that something DOES happen--even to someone who thinks they're safe because nothing ever happened to them.

What last line says is I do not know how to use PROPER magnet size for antenna in question, not that concept is unsafe. Use CORRECTLY sized magnets and you will have no problems.


I can also attest to the paint issues that are mentioned in the first paragraph.  I had the use of a company car where I used a magmount, and I had to get it repaired where the magmount had damaged the paint--or I had to pay up front when turning it in.  

Improperly sized magnet will walk on car over time and damage paint some. With a properly sized magnet it will not walk. I use over-sized magnet mounts with a thin vinyl pad on them and problem is minimal.

Magmounts certainly are convenient--but is that convenience worth someones life?  I think not.

I want you to find one time were someone was killed by these magic flying magnets. You have a better chance of killing someone from a mistake you make driving than from a magnet mount on your car. Are you going to stop driving too to "save a life"?


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K0BG on December 16, 2011, 06:33:14 AM
Justifying using a mag mount by comparisons to the size or the number of the magnets borders on inanity. First of all, one would have to know the exact capacitive reactance of any specific mag mount. That's a bit difficult to measure, and calculating same will only get you close. Whatever the capacitance, there will be some resistive component, and that resistive component will add ground loss.

Over the years, this subject has been beat so badly, the remains almost no longer exist. Perhaps folks should spend some time on Danny Richardson's, K6MHE, web site.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K3GM on December 16, 2011, 08:22:12 AM
I'll forget the "flying missle" argument for now.  After my Larsen Magmount/6m Hamstick incident on the Jersey Turnpike (see previous post on page 1), I went out and purchased a 4 mondo magnet Opec NMO mount to secure the 6m hamstick for temporary operations.  Have you ever tried to get one of those things off the roof of a big SUV when you're standing on a step ladder off to the side of the darn thing!  It's damn near impossible to do it without compromising the finish.  So now I've got a third NMO hole installed in the roof of my Tahoe for my 6m weak signal hamstick, and a 4 magnet NMO mount for the flea market table out at  Dayton this year.  Flying missles aside, mag mounts sooner or later damage the paint finish.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 16, 2011, 09:32:39 AM
Flying missles aside, mag mounts sooner or later damage the paint finish.

Sooner or later car is going to wear out too. The bigger the magnet, the less it will walk on body and scratch paint. They should be removed for time to time and cleaned to get dirt and moisture than build up under them and re-wax surface or car where magnet sits before replacing it.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W6ZPC on December 17, 2011, 05:58:09 AM
Back in my, dare I say it, CB days, I had a mag mount antenna with a center loading coil on it. The only time it came off was when I passed a semi coming the other way and his wind gust knocked it off the roof. It never came off otherwise. I now have a two meter quarter on the roof and the only time it came off was when there was two inches of ice on the roof and it partially melted and slid off the roof, taking the mag mount and antenna with it. Like a previous poster, the antenna slid down the driver's side door and ended up sticking out horizontally from the door.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K1CJS on December 20, 2011, 06:22:12 AM
Since my last post here seems to have disappeared, I will say only this.  There are those who think they have all the answers but are sadly lacking in the practicality/safety departments.  It's a shame that those people insist on pushing their ideas as correct while recommending them to others--and causing those others to ignore the consequences of cutting corners and doing things the easy way.  I wish those people who push their ideas would get a taste of suffering the consequences of those ideas--the consequences that others have suffered or will suffer in following them.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 21, 2011, 09:31:12 AM
Since my last post here seems to have disappeared, I will say only this.  There are those who think they have all the answers but are sadly lacking in the practicality/safety departments.  It's a shame that those people insist on pushing their ideas as correct while recommending them to others--and causing those others to ignore the consequences of cutting corners and doing things the easy way.  I wish those people who push their ideas would get a taste of suffering the consequences of those ideas--the consequences that others have suffered or will suffer in following them.

And then there are those that preach gloom and doom and yet cannot site one incident of a magic flying magnet hurting someone or someone being sued over it. Point is if you PROPERLY size magnet(s) to antenna you will not have any problem but some have trouble grasping this. Most magnets that come standard with antennas that include them are not up to job.  This is where some misconceptions about magnet mounts come from.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K0BG on December 21, 2011, 10:07:37 AM
John, I agree with Chris.

Anyone can justify anything they wish. Some maligned people even justify murder. But whatever you personally justify, is not prima facie for the rest of us.

It isn't whether they stay put or not, scratch or moon the paint, or never fly off, or whatever justification you wish to use. For me, it is the loss in efficiency, and the common mode issues which go along with using mag mounts. Those are factors you cannot justify even if they do not affect your installation. Dispute as you see fit, but the mobile cognoscenti know better.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 21, 2011, 01:34:01 PM
John, I agree with Chris.
Anyone can justify anything they wish. Some maligned people even justify murder. But whatever you personally justify, is not prima facie for the rest of us.

Again even you Alan cannot quote one case of anyone being hit or hurt by one or being sued over it. Lots of people have been hit or hurt or killed by cars. Are you going to park yours to make sure you never hurt anyone with it because statistic say odds are far higher of that happening?

It isn't whether they stay put or not, scratch or moon the paint, or never fly off, or whatever justification you wish to use. For me, it is the loss in efficiency, and the common mode issues which go along with using mag mounts. Those are factors you cannot justify even if they do not affect your installation. Dispute as you see fit, but the mobile cognoscenti know better.

I have used them on HF and even VHF with a 7 foot collinear and it worked great. On HF it worked great when traveling out west with a hamstick on roof of suburban at times. Never needed or used a tuner and always got excellent signal reports for a mobile. Alan your dog just does not hunt.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K0BG on December 22, 2011, 06:20:54 AM
From your response, it is evident you didn't read very carefully.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K3GM on December 22, 2011, 06:15:04 PM
........I have used them on HF and even VHF with a 7 foot collinear and it worked great. On HF it worked great when traveling out west with a hamstick on roof of suburban at times. Never needed or used a tuner and always got excellent signal reports for a mobile.......

But John.... you also claim your 1/4 wave HF vertical works great without radials!  hi hi


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 22, 2011, 08:07:54 PM
........I have used them on HF and even VHF with a 7 foot collinear and it worked great. On HF it worked great when traveling out west with a hamstick on roof of suburban at times. Never needed or used a tuner and always got excellent signal reports for a mobile.......

But John.... you also claim your 1/4 wave HF vertical works great without radials!  hi hi

Perhaps you should schedule a contact sometime and find out how well it does work. I get some excellent reports on 40 where I spend most of my time. it is not quite as strong on 20 and above.  I do not know if it is because it is on a hill or if the soil conductivity is good or a combo of both but it does work well.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KI4SDY on December 23, 2011, 06:25:22 AM
While following this string, I have been conducting some research through the appropriate government agencies, including the one named by KOBG, who cited "one death and less than 50 reported injuries" in his original statement.

Lyn Cianflocco of the National Highway Traffic Safety Administration, National Center for Statistics & Analysis, Data Reporting and & Information Division, states the following; "NCSA has received your request for any deaths and/or injuries caused by magnetic communication antennas on the exterior of vehicles coming off the vehicles. Unfortunately, our files do not get that identified as to the data you are looking for. I am not sure what agency, if any, would be able to provide that data."

In short, they do not have any records and or statistics of such incidents involving magnetic antennas.  :o

I also contacted the National Safety Council who referred me to the Consumer Product Safety Administration. They do not have any records of such incidents involving magnetic antennas either.  :o

In my own 25 years of public safety, I do not know of any deaths and or injuries that resulted from a magnetic antenna coming off of a vehicle and used such antennas on police vehicles at speeds up to 140 MPH chasing criminals without a single incident of an antenna releasing. We also relied on such antennas for life and death communications with excellent results and performance. This was at a time when public safety communications were on lower bands and the antennas were physically longer.  8)

I have also used them privately on my own vehicles for about 40 years and have experienced the same reliable good performance although, if possible, I do prefer a permanently mounted antenna.  :)

Having stated all of that, I would like to know specifically where KOBG's supposed statistics came from and I would like as much detail as to the source as I have provided. Always be suspicious when someone, who seems emotionally attached to a given subject, starts citing statistics without giving the specific source of his information!  ;)

People can always mount an antenna that defies the laws of physics on their vehicle, whether permanent or magnetic mount, and have a mishap. We have seen testimony to that here. This has more to do with the safety of the operator and less to do with the safety of equipment. ;D
 


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K1CJS on December 26, 2011, 03:25:18 AM
John,  Do you also still insist that it is OK to use undersize wiring to feed a load as long as you use a capacitor at the load end to even out the voltage drop?  AS I said, some people are sadly lacking in the practicality/safety aspects of all too many things.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 26, 2011, 05:05:42 AM
John,  Do you also still insist that it is OK to use undersize wiring to feed a load as long as you use a capacitor at the load end to even out the voltage drop?  AS I said, some people are sadly lacking in the practicality/safety aspects of all too many things.

If by undersize you mean not using wire that is greatly over-sized for circuit load, yes. Example, you do not need to use 6 or 8 ga wring for a 20 amp radio load but judging by your tone and loss of magnet mount spat you looking for a new confrontation and are likely implying I suggested wire truly undersized (rated current capacity) for circuit load but I have never suggested that.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K1CJS on December 27, 2011, 06:30:38 AM
No, no new confrontation.  Thank you for the answer.  My point is made.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 27, 2011, 10:10:03 AM
No, no new confrontation.  Thank you for the answer.  My point is made.

Yes you made point alright but not one you thought.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: G7DIE on December 27, 2011, 01:29:49 PM
That last line says it all.  The safety factor should be the one thing that would preclude the use of magnet mounts on a moving vehicle.  No matter how many miles someone claims to have travelled with no issues, there is always tomorrow.  And tomorrow may well prove to be the day that something DOES happen--even to someone who thinks they're safe because nothing ever happened to them.

I can also attest to the paint issues that are mentioned in the first paragraph.  I had the use of a company car where I used a magmount, and I had to get it repaired where the magmount had damaged the paint--or I had to pay up front when turning it in.  

Magmounts certainly are convenient--but is that convenience worth someones life?  I think not.

I'm employed as an Aircraft Engineer with a UK airline, we operate both Boeing and Airbus aircraft, fitted with Rolls Royce, General Electric, International Aero Engine, and CFM International engines, they ALL use historical data in order to review service intervals and life limitations, hours on wing, cycles, flight hours etc etc, time between failure, mean time between failure are all methods to establish reliability, indeed there is always tomorrow, will you now be giving up flying, driving, walking?

Just a thought  ;)


Title: RE: Magnet Mounts....Just how safe are they????
Post by: K1CJS on December 30, 2011, 06:13:22 AM
I'm employed as an Aircraft Engineer with a UK airline, we operate both Boeing and Airbus aircraft, fitted with Rolls Royce, General Electric, International Aero Engine, and CFM International engines, they ALL use historical data in order to review service intervals and life limitations, hours on wing, cycles, flight hours etc etc, time between failure, mean time between failure are all methods to establish reliability, indeed there is always tomorrow, will you now be giving up flying, driving, walking?

Just a thought  ;)

No, I won't.  My point is simply this.  There are always people who either don't stop to think about a magmount holding power--or who simply don't care.  Then, when something happens, they're the first to b*tch, moan and complain to the dealer, the manufacturer--and even to the court system about how 'unsafe' products are allowed on the market.

Added to that, some people will modify those magmounts with things to prevent damage to the paint finish of cars, and in the process, inadvertantly change the design specs so the magnetic holding effect is lessened.  Those people won't think about that, and figure that the advertized grip of that magnet is still the same.  Next thing they know, the mount is being dragged along behind (or beside) them by its coax.

Others will figure that they can 'get away with' a mount that isn't really meant to be used with an extended length antenna, or a mount that has a disclaimer, "not to be used at highway speeds" and the same thing will happen.  There use to be a so called 'magmount' offered for sale that had a nineteen inch thin whip on it--and the magnet was less than the size of a half dollar!  (This is the one that had the disclaimer on it.)  There are people who would still buy it and use it no matter if they travelled a city or country road--or a highway.

For every one or two people who take the time to make sure of the so called 'trivialities' of these things, there are a dozen or more that do not.  Nothing will ever happen to them--and look out for them and the fallout they would cause if something does.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KI4SDY on December 30, 2011, 08:50:19 AM
The last post, like the former that I responded to, has no verified statistics by any official agency concerning the claims made. It is only opinion from someone who, for unknown reasons, is emotionally against the use of magnetic antennas, despite their popular use for decades without even one verified injury or death! Had there been any such events, the army of lawyers in this country would have sued the makers of magnetic antennas out of existence. I challenge the last poster to verify, with just one public record, any lawsuit regarding a magnetic antenna!  ;)

In fact, even the antenna "that had a 19 inch thin whip on it -- and the magnet was less than the size of a half dollar" that was referred to is still made by MFJ and others. We are currently using it on the lady ham's Mustang's rear narrow fender (MFJ-1722). It has given excellent performance and has never come off, even though we added a disc of self-stick scuff coat tape to the bottom to reduce the extremely strong hold of the magnet so it can actually be removed to periodically wash underneath. Still, we have have experienced no antenna problems, after years of use with her lead foot at highway speeds. Believe me, that is an acid test for failure! Again, here is the same person commenting on a piece of equipment he has never owned or used.  ::)

The National Highway Traffic and Safety Administration has published a statement from the U.S. Transportation Secretary Ray Lahood, who stated in 2009, vehicle related deaths fell to 33,000 for the year of 2009. A decrease even while miles driven increased .2% over 2008 levels, some states no longer requiring motorcycle riders to wear helmets and people using cell phones behind the wheel. With the increase in the number of hams, many who are using magnetic antennas, deaths should have risen if this was a real hazard. Again, there are no deaths or injuries reported by this government agency as a result of magnetic antennas, regardless of the previously posted erroneous information. According to the NHTSA's actual statistics, these magnetic antenna safety condemners should park their cars and start walking if they want to save lives!  ;)      


Title: RE: Magnet Mounts....Just how safe are they????
Post by: W8JX on December 30, 2011, 05:07:14 PM
The last post, like the former that I responded to, has no verified statistics by any official agency concerning the claims made.

I think K1CJS is his own "official" agency and has his own trumped up statistics.


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KE4DRN on December 30, 2011, 06:36:28 PM
hi,

I remember all the CB mag mounts from the 1970's on all the cars,
if the mag mounts were a real danger we would have data on that.

I am more worried about that handyman truck in front of my car
on the highway with half a dozen ladders held down with a few
sun bleached bungee cords.

73 james


Title: RE: Magnet Mounts....Just how safe are they????
Post by: KI4SDY on December 31, 2011, 02:34:41 AM
A matter of fact, I have a collection of rubber bungee cords from those "handyman trucks" that I picked up off the road and keep in my truck tool box for emergencies. I throw the bad ones away and keep the good ones. I pick them up to keep the S hooks from piercing people's tires. Still, no record of anyone being injured or killed by flying bungee cords. The flying ladders may be another matter! ;D