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eHam Forums => Mobile Ham => Topic started by: K5END on June 17, 2009, 11:37:40 AM



Title: Mag Mount Surety
Post by: K5END on June 17, 2009, 11:37:40 AM
For those who doubt mag mounts can come off a vehicle, I assure you they CAN.

It happened to me several years ago. The antenna was then dragged by the coax under the rear tire, and the tension snapped the coax promptly.

Based on the loud racket it made as the assembly was thrown against the underside of the car I was quite relieved that no one was injured and no property was lost--except the antenna.

I went back to clear the debris from the road but could not find it. Either it disintegrated completely or it was thrown beyond the roadside.

Now, I do understand there are some multi-magnet mounts out there that are difficult to remove. I'm not going to debate that.

The point is, use extreme caution.


Title: Mag Mount Surety
Post by: K0BG on June 17, 2009, 02:23:49 PM
About two years ago, I stopped in Tatum, NM to gas up. There was another vehicle there with a Hustler antenna which had three coils on it (spider mount). It was held on the trunk by a tri-mag mount from MFJ. There were two guy ropes attached to the antenna, running through the rear doors, and tied in the middle. When I ask him about the guy wires, his reply was, Oh, it's come off a few times! Thank the Lord for small favors, that I wasn't behind him when it did.

Alan, KØBG
www.k0bg.com


Title: Mag Mount Surety
Post by: WB2WIK on June 17, 2009, 02:29:37 PM
Even the 3 and 4 magnet mounts can come off if they have a long or top heavy load on them.  With a 2m whip, nah -- they'd stay put.  But I've seen 3-4 magnet mounts used with things like Outbackers and Hustlers with top resonators and such: This is a disaster waiting to happen.

I have a "tri-mag" mount that has three large (4" diameter, circular) magnets.  Once on the roof, if I try with all my might to pull it off: No way.  Can't do it.

However if I put my Hustler MO-2 mast with a 40m resonator on it into that mount, and tilt the top of the Hustler near the resonator, I can "tilt" the mount off with just the pressure applied by one arm and my fingers.  Easily.

Hitting the car ahead when going 20-30 mph and coming to an abrupt stop like that easily reproduces that kind of force -- and then some.

Not a pretty sight for a 10 lb magnetic base and frame, with a long antenna attached, to go flying off the roof.  Almost anything it lands on will be very damaged.  If that's someone's windshield or head, I wouldn't want the lawsuit that follows.

Mag mounts are for *temporary* use when it's deemed safe to use them temporarily.

WB2WIK/6


Title: Mag Mount Surety
Post by: K1CJS on June 18, 2009, 05:09:42 AM
"Mag mounts are for *temporary* use when it's deemed safe to use them temporarily."

Agreed!  The only places for their use is on a stopped, parked vehicle--or on a flat metal surface that doesn't move, such as a file cabinet.


Title: Mag Mount Surety
Post by: K5END on June 18, 2009, 08:03:20 AM
"on a flat metal surface that doesn't move, such as a file cabinet"

AMEN.

Instead of a file cabinet, I use mine on a big ol' Liberty gunsafe sitting on the concrete floor of the shack. (Yes, I have another gunsafe in the house, for quick access--in case any crooks are reading this, hihi.)

Works more or less OK for 2 m and UHF, especially for reception.

I also use a mag mount for VHF/UHF on a steel patio roof about 14' x 14'.

That actally works pretty well from 50 MHz and up.


Title: Mag Mount Surety
Post by: W0FM on June 18, 2009, 12:24:00 PM
"on a flat metal surface that doesn't move, such as a file cabinet"

Or a refrigerator!  Refreshments close at hand.  :o)

Terry, WØFM


Title: Mag Mount Surety
Post by: KI4SDY on June 19, 2009, 08:42:57 AM
The Egyptians built the pyramids broad base down for a reason. A pyramid placed on its point will not stand!

You have to use some common sense when installing any antennas, whether they are magnetic or permanent mount. A permanent mount antenna, that is physically top heavy, is no more stable or safe than a magnetic antenna of the same profile. The bad thing about permanent mount top heavy antennas is that when they fail, they bend and tear the metal on the car, causing increased damage. Further the so called permanent mount is a weak point in the structure, with no cable attached after failure, turning the antenna into the often fabled deadly missile. I have seen posts on this net of hams complaining, after they bought a tall multi coil or other top heavy antenna and mounted it on the roof, that it fell apart after hitting a tree limb or encountered heavy wind resistance. The only thing I can say to that is; not too dumb! What did you think was going to happen? I am seeing similar posts on this thread using magnetic mounts, because it is populated with the hole drillers club.

The type of mount does not matter if the installation defies physics. It will fail!