Vehicle Antenna Blowover

[Dan Rupnow]

I recently got my cellular amp/antenna combo for my aircard in my car, and while the amp/antenna work awesome for boosting signal, the antenna doesn't like to stay put at higher speeds. I had the antenna come off a few times while doing around 70mph. Also I have had it come off when meeting a semi on a two lane road. I realize semis push a lot of wind, but am thinking the antenna should be designed with a strong enough magnet to handle it. It is very aggravating when trying to keep up with a storm to have to stop and stick the antenna back upright again. I had the antenna mounted on the roof, but am thinking of putting it on the trunklid to help get it out of the wind.

Does anyone else have this problem?

 

[Jesse Risley]

Yes, that happens, even with some communications antennas that have magnets with a greater surface area. I would strongly suggest considering some form of more permanent mounting option, or at the very least an alternative magnet mount with a larger surface area.

I briefly reviewed some alternative mounting options with picture links in this article.

 

[James Hammett]

Through-hole NMO mount. I took the plunge and cut into my shiny new car's roof last year. No more concerns about antennas flying off or how to get the wires routed to the interior. Gives you a better ground too if you need it. I also tend to think it helps keep a lightning strike from entering the vehicle by eliminating all the wires running along the exterior into the interior.

 

[John Erwin]

I had that happen a few years back with a scanner antenna I was using. In that case I ended up placing it near the luggage rack on my vehicle and ty-wrapping it down and it worked for that trip. Since then I've pretty well gone to permanently-mounted style antennas so it's no longer an issue.

 

[Josh VandenTop]

I have 2 magnetic mount antennas and haven't had any problems so far, even when passing trucks. Although after reading some threads here about other people having problems I have wrapped the cables around the luggage rack just in case. After reading this what worries me now is my magnetic mount light bar, I haven't done alot of driving with that on so I'm not sure how that one will react.

 

[Gordon Spencer]

Easy Solution - Very small dab of silicone at side of the base of the antenna. That way no drilling holes in your car and if you wish to remove , you just remove the silicone with a razor blade.

I recently got my cellular amp/antenna combo for my aircard in my car, and while the amp/antenna work awesome for boosting signal, the antenna doesn't like to stay put at higher speeds. I had the antenna come off a few times while doing around 70mph. Also I have had it come off when meeting a semi on a two lane road. I realize semis push a lot of wind, but am thinking the antenna should be designed with a strong enough magnet to handle it. It is very aggravating when trying to keep up with a storm to have to stop and stick the antenna back upright again. I had the antenna mounted on the roof, but am thinking of putting it on the trunklid to help get it out of the wind.

Does anyone else have this problem?

 

[Dan Rupnow]

Thanks for the responses, I will try out some of the mentioned remedies.

 

[Joshua Nall]

Easy Solution - Very small dab of silicone at side of the base of the antenna. That way no drilling holes in your car and if you wish to remove , you just remove the silicone with a razor blade.

That sounds like an excellent remedy. I was just thinking this week there has to be a simple fix. I've never had it to come completely off, but it has jumped around and scooted back in high winds. I think I'll put a bead all the way around it.

Josh

 

[Mike Bennett]

Easy Solution - Very small dab of silicone at side of the base of the antenna. That way no drilling holes in your car and if you wish to remove , you just remove the silicone with a razor blade.

Gordon, If I found and purchased a stronger magnet to go between the antenna magnet and the vehicle would it possible weaken the ground and ultimately affect the effectiveness of the antenna?

I did this for my amber strobe and it really strengthened the grip it had to my vehicle.

 

[Gordon Spencer]

Should work , I don't think it would effect performance

Gordon, If I found and purchased a stronger magnet to go between the antenna magnet and the vehicle would it possible weaken the ground and ultimately affect the effectiveness of the antenna?

I did this for my amber strobe and it really strengthened the grip it had to my vehicle.

 

[Bryan Stokes]

Easy Solution - Very small dab of silicone at side of the base of the antenna. That way no drilling holes in your car and if you wish to remove , you just remove the silicone with a razor blade.

Great advice Gordon! Thanks for sharing!

Bryan

 

[Dave Marshall]

I had the same problem with several antennas and eventually a light bar. Some lessons from a ham who has way too many antennas, and has smashed a back window out when one came loose (these were mostly learned the hard way):

1. Never trust the magnet on a Radioshack antenna. Ever.
   
   
2. See Rule #1
   
   
3. Overkill is never a bad thing. Ham radio supply companies like HRO sell bunches of high quality, powerful magnet mounts that will fit any antenna. You can find them at hamfests as well.
   
   
4. Rare Earth FTW! If the magnet is the brittle black fridge magnet sort (ferrous), it's nearly worthless. Even the largest ones will lose strength within 3 years, they'll also cause rust stains on your paint. Neodymium magnets are more expensive, but last decades, and don't need to be as big. You can spot these because they almost always have a bright, shiny, smooth appearance, and they're inordinately strong.
   
   
5. Roof rack mounts are fine for receiving antennas. When transmitting, without a proper ground connection they are frequently sub-optimal or even outwardly dangerous to your radios (SWR kills!).

The silicone adhesive idea sounds pretty solid, but be careful not to completely coat the magnet with it. Many antennas only perform really well when they are close enough to the car body to couple capacitively to the sheet metal through the mag mount or connect directly using a permanent thru-hole mount. Like the roof rack, care has to be taken to ensure the antenna still has a sufficient ground. Silicone caulk is a damn fine insulator.

EDIT: Mike, So long as the new magnet is still connected by metal-to-metal contact with whatever bolt/screw/joint that connected the original magnet to the antenna, it will still be a part of the antenna's ground plane and performance won't suffer any. The shield of the coax is actually connected to the metal base of a magmount antenna, meaning the magnet is electrically a part of the antenna as well.

 

[Josh VandenTop]

Gordon, If I found and purchased a stronger magnet to go between the antenna magnet and the vehicle would it possible weaken the ground and ultimately affect the effectiveness of the antenna?

I did this for my amber strobe and it really strengthened the grip it had to my vehicle.

What type of stobe do you have? and what kind of magnet did you get? I'm starting to become concerned if my is going to stay put or not.

 

[J West]

As an equipment installer, I always recommend permanent mounting first whether it's an L bracket on a fender (meh) or an NMO mount (best). Anything permanent is better than a magnet of any kind.

As a vehicle owner, I understand that not everyone wants to put 3/4" holes in their personal vehicles. Public safety vehicles however get as many holes as needed. If a department doesn't want to go that route, I personally won't do the work.

You will need to make the determination for yourself whether you want the hole in the vehicle or not. You can't go wrong with a properly installed NMO mount and antenna though. It is the best antenna mount as far as strength, durability and antenna performance.

EDIT: Mike, So long as the new magnet is still connected by metal-to-metal contact with whatever bolt/screw/joint that connected the original magnet to the antenna, it will still be a part of the antenna's ground plane and performance won't suffer any. The shield of the coax is actually connected to the metal base of a magmount antenna, meaning the magnet is electrically a part of the antenna as well.

Ground plane, yes...proper grounding? No. Unless the the mount is physically connected to the vehicle body, it is not grounded nor is the antenna electrically part of the vehicle. NMO mounts accomplish this through the botton half of the mount where the ears are in contact with the underside of the sheetmetal, where external mounts for HF antennas need to have a ground strap run to the body in order for the antenna to even attempt to function.

Ground planes and grounding is everything as it pertains to antenna performance.