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Fixed Wireless Technology

Magnets Beyond the Refrigerator

Sure, magnets put all sorts of cute characters on your refrigerator door, but who would have suspected they could be involved in broadband fixed wireless access? Some members of the ISP-Wireless list have used them for years.

[October 1, 2002]

On the ISP-Wireless list in August, BR queried,

"I've heard of people using magnets for mounting on water towers or objects that can't be penetrated. Can someone give me an idea on how to mount antennas using magnets?"

FC suggested considering epoxy instead of magnets:

"That would have to be one heck of a magnet to stop any significant antenna from moving when the wind gusts. We use epoxy to mount to water towers when a suitable clamping spot is not available. Even have a couple of normal 3 foot tripods that are just epoxied straight to the tower. I've got one of these with a radio box, 24 dBi grid, and an omni, all mounted to the tripod—solid as a rock. If it's hot, one of the gel epoxies is easiest to work with (stays where you put it). Just make sure you prep the surface well and make sure there is no oil on either surface."

JH asked for clarification:

"Do you remove the paint down to bare metal? And how do you deal with the grounding issue when you're using epoxy rather than bolting?"

FC duly clarified:

"Generally, I do remove the paint down to bare metal. If it's got an epoxy-based primer that is in real good shape, then I've left the primer (and that's directly on the metal), but otherwise I take it down to bare metal. Be sure your epoxy covers the entire area where you remove the paint. And we run a ground wire to a suitable location: light support, vent, ladder, etc."

Others returned to the original question and suggested some good sources for magnets:

[IS advised] "I like rare earth servo magnets removed from old hard drives. I have some that came out of 120 MB hard drives, which have a nice metal backing plate with three holes. I plan on fabricating a mount for my antennas, then riveting these to the mounting plate. The magnet cost is minimal, and they are really strong."

[BE offered] "ForceField is the most reliable and cheapest source for magnets of any size that I have found. I buy a lot of magnets for various reasons, and have rarely had them not have what I wanted."

ES contended that there's no problem using magnets to mount an antenna:

"I have four sites that are currently magnetically mounted. I use cup magnets from Industrial Magnetics. The magnets that I use have 100 pounds of holding power each. There is a 3/8 inch stud in the middle that I put through the feet of a tripod. I use one magnet per leg for light stuff, and two magnets per leg if I am going to install a 24 db parabolic. I have water towers with three tripods all connected with 1 inch galvanized pipe using two magnets per leg for sectorized sites. I have had painting crews call the landlord and complain about how hard the magnets are to move around. We check them monthly for movement, but as of yet they have been up through 70 to 80 MPH thunderstorms and have not moved enough to notice."

—End