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eHam Forums => Mobile Ham => Topic started by: W6NZX on March 27, 2009, 09:37:31 PM



Title: Increasing efficency of a mag mount.
Post by: W6NZX on March 27, 2009, 09:37:31 PM
Increasing efficency of a mag mount.

I hardly ever get on 2M/70CM anymore, so I sold off my 2M rig and kept my VX-2R.

Great little radio and I can get into MOST of the repeaters here in the Utah valley, however I'm no where near full quieting and people say I drop in and out.  I have one of those cheapie imported mag-mounts and i'm wondering if there is anything I can do to make it "work" better.

I ask, because I had an AMAZING experience with the VX by adding a metal ring and wire equal in length to the portable antenna and putting it between where the antenna screws on and the insulator to the frame.  I.e. I made the other half of the circuit larger--the vx-2r has a small body.

So, can I do something similar when using the mag-mount?  a LONGER wire?  ANYTHING to mak the mag-mount bigger?

DE W6NZX SK 0436Z


Title: Increasing efficency of a mag mount.
Post by: K0BG on March 28, 2009, 04:26:45 AM
Where are you going to connect the other end? To make it effective, it would have to be connected to the body someplace. I suppose you could make a ground plane out of it by using radials as it were, but the wind load would increase, and so would the likelihood of it dislodging. Why don't you just drill the hole, and do it right?

Alan, KØBG
www.k0bg.com


Title: Increasing efficency of a mag mount.
Post by: W6NZX on March 28, 2009, 07:03:51 PM
I was actually thinking of having a heavier wire running from the "frame side" of the vx to one of the bolts holding the seat against the frame, that would give me a big hunk 'o metal.

I think my real problem was the last car I had this setup in was a Chevy cavalier lots more metal to reflect that signal--now I'm in a GEO metro and my HT is almost useless, and the price of mobile amps, makes just buying a mobile make more since.

But I'm a cheap-skate :-)


-Rob


Title: Increasing efficency of a mag mount.
Post by: KI4SDY on June 08, 2009, 06:35:04 AM
Your not telling us how far away the repeater is so that we can make a judgement on the performance of your setup.

Right off the bat, the most inexpensive and effortless thing you can do is to buy a better magnetic antenna. I would suggest the MFJ-1729 power gain dual band antenna. It is highly rated on eHam.net and locally here. You can place it on the roof for maximum range or on the trunk for garage clearance. In addition you can move your rig from car to car or set it up as a portable base at home.

If you don't use VHF/UHF that much, I wouldn't drill holes in the car to install an antenna. It isn't necessary.


Title: Increasing efficency of a mag mount.
Post by: AA4PB on June 08, 2009, 09:56:54 AM
The larger dia the mount, the more capacitive coupling there will be to the metal roof.


Title: Increasing efficency of a mag mount.
Post by: K5END on June 08, 2009, 10:49:20 AM
You are mounting an antenna on the exterior of the vehicle, and not trying to use the HT antenna on the interior, right? That's my first question. Anything below a couple of GHz really needs the antenna exterior to the vehicle.

As far as the other stuff, I agree with Alan on this topic.

Unless it is a borrowed or rented car, or something like a pristine 1935 Super V8 Packard sport coupe, of which there are only a half dozen in existence, just drill a dang hole (and you wouldn't be putting a mag mount on that Packard anyway.)

When possible, drill and do it right. Beware of existing wiring, structural members, air bags, sunroof mechanism, weatherproof, etc; you get rain in UT, from time to time, right?

Metal to metal joint to a bonded car body beats capacitive coupling at any frequency. Mag mounts are just a convenient hack.

In the long run, mag mounts will mess up your paint much more than a pluggable 13/16" hole and they present a safety hazard.


Title: Increasing efficency of a mag mount.
Post by: KI4SDY on June 16, 2009, 07:47:32 AM
K5END said; "In the long run, mag mounts will mess up your paint much more than a pluggable 13/16" hole and they present a safety hazard."

Not if your read and follow the instructions that tell you to remove the antenna when you wash the car and replace it when dry. Of course, that would be for people that actually wash their car, assuming it would make their hole ridden heap look better.

I can't think of anything that will mess up your paint more than drilling a hole in the car. Sticking an ugly  rubber plug in it doesn't fix the paint either!

As far as the safety hazard, that is an old wives tale (like global warming) that has no statistical basis. Ignore the hole drillers that spout this silly scare tatic.

If you permanently mount the antenna you also lose portability to move the rig from car to car or as a portable base. The antenna I suggested has been used for both. Just place it on top of a metal file cabinet or ther large metal object. Remember to check the SWR!


Title: Increasing efficency of a mag mount.
Post by: WW5AA on June 16, 2009, 01:16:07 PM
"As far as the safety hazard, that is an old wives tale (like global warming) that has no statistical basis. Ignore the hole drillers that spout this silly scare tatic."

You might let the motorcycle rider who got hit last year by a mag-mount CB antenna that bounced off the street and cut his chin pretty good know about this silly scare tactic. I don't know about the statistics, but with 40 years in Law Enforcement, I have seen several. By the way, the lawyer on this case doesn't care about statistics either.

73 de Lindy


Title: Increasing efficency of a mag mount.
Post by: K0BG on June 17, 2009, 05:48:54 AM
Larry, if you care to, you can look up the crash which killed a 75 year old women in Cincinnati. If my memory is correct, is was April 2004.

The other known fatality was listed on the NHTSA statistics page. This one occurred after the NHTSA required reporting telemetric use. It occurred in 2006.

As Lindy alluded to, there have been dozens of others which didn't fall under the fed reporting mandate.

This brings up a side light.

Folks drive around with all manner of heavy objects laying around in their vehicles. Brief cases are a good example. You don't read about these objects flying about the vehicle during a crash or evasive maneuver; the fed doesn't mandate such things. However rare, this very thing has happened to me, and I have the scar to prove it! After the incident, I started buckling my brief case in with the passenger seat belt. Over kill you say? I personally don't think so.

On my web site, I admonish folks for using Velcro to attach all manner of devices. Yet, the interior trim of most modern vehicles are held in by the stuff. But, there is a vast difference between a 4 ounce piece of plastic, and a 4 pound radio!

As I recently stated on these pages, the odds may be slim, but like getting hit by lightning (the proverbial chance in a million), it does happen quite regularly.

Speaking only for myself, I prefer to walk on the safe side, even if that means facing the traffic!

Alan, KØBG
www.k0bg.com


Title: Increasing efficency of a mag mount.
Post by: AA4PB on June 17, 2009, 06:36:13 AM
Where you mount the radio, even if firmly attached, can have serious results as well. Many years ago my wife did serious damage to he knee in an accident when her leg hit the CB radio mounted under the dash. I also have wondered about the results of an air bag deployment hitting the edge of a center mounted radio.


Title: Increasing efficency of a mag mount.
Post by: KI4SDY on June 17, 2009, 07:28:55 AM
WW5AA said; "You might want to let the motorcycle rider who got hit last year by a mag mount CB antenna that bounced off the street and cut his chin pretty good know about this silly scare tactic."

I would be interested to know how the CB antenna came off the car with the coax cable attached! How about giving me the accident report number for that incident so I can get a copy? I would also like the accident report numbers for the "several" other mag mount accidents that you reportedly saw in 40 years. Maybe they have a phenomenon of these things in Arkansas, like the Bermuda triangle. After 25 years of law enforcement, I never saw or heard of anything like that with magnetic antennas, including my own, that stayed on the patrol vehicle at 140 miles per hour while I was chasing criminals.

One thing I learned after many years of law enforcement was the biggest tellers of fish tales wear a badge. Old timers are especially bad about this because they figure the records are gone and nobody can check up on their stories. Unfortunately, I have seen bad police department policy created as a result of these urban legends.


Title: Increasing efficency of a mag mount.
Post by: K0BG on June 17, 2009, 10:59:18 AM
Vern, one of the problems finding data on crashes, is the lack of data bases. It wasn't until 2005 that the NHSA mandated telemetric use on crash reports. Even then, there are a lot of crashes where telemetrics were in use, but didn't end up on a police report for whatever reason.

I found the one in Cincinnati, quite by accident, if you'll excuse the pun. The report on the second one was via e-mail.

You ask how an antenna could fly off when it is connected by a coax cable. Well, weigh a mag mount antenna, take your 140 mph report, and calculate the kinetic energy. You just might be surprised to find out just how much there is. Even at 60 mph, an average weight 2 meter transceiver will have hundreds of pounds of kinetic energy. Obviously, not all of the energy would be expended before it hit an occupant, but one thing is for sure. Enough is left to main and kill. Whether it does is moot.

Alan, KØBG
www.k0bg.com


Title: Increasing efficency of a mag mount.
Post by: K5END on June 17, 2009, 11:17:42 AM
>
"Larry, if you care to, you can look up the crash which... "

Alan, I agree with you about mag mount hazards.

Are you preaching to the choir? hihi

73
LK


Title: Increasing efficency of a mag mount.
Post by: K5END on June 17, 2009, 11:24:29 AM
Personal experience with a mag mount coming off.

About 10 years ago I had a mag mount cell phone antenna, and had snaked the coax through the door gasket to the exterior roof.

For some unknown reason the mount came off and was dragged by the coax.

Because it was held in place by the door, the assembly was dragged under the rear tire. The tension on the coax between the door and the tire promptly snapped that coax right off and made a heck of a racket under the car.

I went back to clear the antenna remains from the road but never did find it. I'm happy no one was hurt and the only loss was the antenna itself.

The coax is plastic and copper. It doesn't take much tension to snap it.


Title: Increasing efficency of a mag mount.
Post by: KI4SDY on June 17, 2009, 07:24:45 PM
I haven't seen or experienced any of these flying mag mount phenomena. Maybe I am better at placing antennas on a car than you. If the placement looks like it defies the laws of physics, it probably does. You have to use some common sense!

I have seen (and I know you have) several permanent roof mounted antennas that are missing the radiator wire, leaving only the mount and or loading coil. This usually results in the radio transmitter being burned up, before the operator realizes the wire is gone.

I have never heard of anyone getting hit in the eye with a radiator wire, but I could start a rumor, like the mag mount stories. Alas, I am not willing to make up stories to make a point on eHam.net, so I guess I will pass on the opportunity. However, permanent mount antennas have the potential to be just as theoretically "dangerous" as mag mounts!

I would have a better chance of being a global warming victim than being killed by flying antenna parts! Find better reasons to talk neophyte hams into drilling holes in their cars when it is not necessary or even convenient.


Title: Increasing efficency of a mag mount.
Post by: K5END on June 17, 2009, 09:57:07 PM
>
Thanks for sharing.


Title: Increasing efficency of a mag mount.
Post by: K1CJS on June 18, 2009, 05:04:11 AM
On some of those mag mounts, the attachment of the co-ax to the mount is not strong at all.  The co-ax doesn't have to break, it can be pulled right out of the mount just by the snap when it reaches the end of travel allowed by the co-ax.

Mag mounts may be handy and portable, but they're also dangerous in some situations that people don't have control over.


Title: Increasing efficency of a mag mount.
Post by: WW5AA on June 18, 2009, 06:36:13 AM
Vern,

I do not keep a personal list of traffic accidents. The first three involving a mag-mount where while serving with the Los Angeles Police Department. The last one is as Chief, Department of Public Safety, DAH-State of Arkansas. The mag-mount was fed through the rear window. It was evident that the base of the mag-mount hit the side several times behind the window before the coax pulled out of the base. While were at it, Think carefully about the suction cup windshield mounts for GPS and cell phones. These are starting to become a problem when traffic accidents are PROPERLY investigated.

73 de Lindy


Title: Increasing efficency of a mag mount.
Post by: KI4SDY on June 18, 2009, 06:42:17 AM
K1CJS said; "On some of those mag mounts the antenna attachment of the coax to the mount is not strong at all." So which antenna companies and antenna models are those? Be useful and give us a list, rather than just posting undocumented statements with no specifics or evidence. Oh, I get it. This is your opinion. Well, we know all how much that is worth!
 
K1CJS said; "The coax doesn't have to break, it can be pulled out of the mount just by the snap when it reaches the end of travel." So how many times has this happened to you? It has never happened to me and the anti-mag mount posters here say their antennas were dragged after they magically fell off for some reason. Another flawed theory based on perception rather than facts!

Many fatal accidents are caused by tire blow outs. Do you still have rubber tires on your car or are you using concrete tires for safety, like Fred Flintstone?

Again, permanent mount antennas and their flying radiators have the potential to be just as theoretically "dangerous" as mag mounts. Don't use safety as an excuse to give beginner hams bad advise!


Title: Increasing efficency of a mag mount.
Post by: KI4SDY on June 18, 2009, 07:41:05 AM
WW5AA said; "I do not keep a personal list of traffic accidents." No, but the department keeps an official list. Give them a call. They will hunt them down for you. If you were a cop, you should know how to get the information to prove your point. No report number, no proven point!

So the "several" mag mount accidents you saw in 40 years is now down to only four! That is only one every ten years. Sounds like an embellishment, at least. Good thing it wasn't under oath. I bet if we keep working on this, we can get it down to none!

If the four mag mount accidents were true, how would it compare to accidents caused by tire blow outs, on a percentage basis? I probably would have a better chance of having an elephant fall on my house, than being killed by flying antenna parts! That reminds me. How many of these mag mount accidents were fatal? None!

No offense, but some of the biggest liars and thieves I ever met were police chiefs. We had one that claimed he fought in every war in the 1900s, but had no military records. His favorite story was the time he parachuted out of a plane, the chute didn't open and he landed in a hay bale, saving his life. A stolen department shotgun was found behind some dry wall in his house after he died, by the new owner. He also conspired to make false allegations against me and was caught lying under oath in the internal affairs investigation. I should have arrested him personally on the spot, but I am a nice guy. Sometimes too nice!

Parachutes not opening, flying mag mounts, what is the difference?

How many permanent mount antennas have you seen with the radiators missing? Be truthful now!


Title: Increasing efficency of a mag mount.
Post by: KD4LLA on June 19, 2009, 12:16:57 PM
Look on ebay for a R/S 30 watt VHF amp.  You can probably find one for around $25.  Or just buy a decent mobile and drill the hole to mount an antenna.

Mike


Title: Increasing efficency of a mag mount.
Post by: K1CJS on July 09, 2009, 08:08:29 AM
SDY--as usual, you're just shooting your mouth off.  Telling a beginning ham that a mag mount is just as safe as a securely attached mount is giving the beginner the WRONG advise, not just bad advise.  Your usual two cents worth isn't worth the two cents your handing out.