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Author Topic: MJF Antenna  (Read 2771 times)

Posts: 1014

« Reply #15 on: October 19, 2005, 11:53:54 AM »

After 21 years plus as a ham I am one of those people Steve, WB2WIK/6 refers to.  I will absolutely, positively NEVER punch a hole in my car.  Period.  End of discussion.

Having said that I still don't recommend mag mounts because they do scratch the paint no matter how you try not to and because they don't work as well as other solutions do.  Alan is correct when he says they are lossy.

My solution has been a Diamond K-400 trunk lip mount.  I've had it for years and it's now been on three different vehicles.  I use it with a Diamond CR-320A or Diamond CR-224A and I highly recommend both the mount and the Diamond antennas.  I was driving through eastern Kentucky on Monday evening and in QSO on the Dorton, KY repeater on 224.52.  I was told I would run out of range at Saylersville.  I was actually well beyond that on the Mountain Parkway and still getting in.  I was told that was the best they had *ever* heard anyone get in from there.  (Clue:  A Diamond CR-224A is a *big* colinear antenna on 222MHz and a 7/8 wave on 2m.)  

My point is that I don't think drilling a hole would make a huge difference in my ability to get into repeaters.  I seem to do as well as anyone else.


Posts: 1014

« Reply #16 on: October 19, 2005, 12:00:38 PM »

To more directly answer the question:  I don't like the way MFJ antennas are built.  However, since you have it already (free is always the best price) I'd just look at a trunk lip mount/hatchback mount to replace the mag mount.

If and when you decide to replace the MFJ antenna in addition to Larsen I would take a good long look at products by Diamond, Comet, and Maldol.  I have Diamond and Maldol products I am very happy with.  When I run HF and 6m in the car (rarely, nowadays) I use a Maldol HMC-6S which covers 40m or 20m plus 15m, 10m, 6m, 2m, and 70cm.  Maldol and Diamond both make some excellent 2m/70cm dual band antennas.  The bigger the antenna the better it likely will perform.


Posts: 5482


« Reply #17 on: October 20, 2005, 09:00:16 AM »

No, I'm not taking it personally, I just have a perspective about this topic that not every ham has.  Most hams' perspectives are limited to their own experience and perhaps a small circle of other hams they know.  When they come upon, or hear of a solution that works, it's considered a done deal.  My perspective comes from when I worked in the 2-way radio business for a number of years.  When you install thousands of radios and antennas, you quickly learn what works, what lasts, and what doesn't.  Even subtle differences in how or where something is routed, mounted or connected can affect reliability and performance.  Because there isn't much money in the install business, you can't afford to have units come back due to installation related issues.  I have seen the cause and effect of just about every mobile radio problem possible.  Mag mounts scratch paint.  They put 'smiles' in the panel from tilting them to get them off.  Metal filings (from brakes?) get stuck to the magnet during travel, compounding the scratching problem, then when water from rain or dew wicks under the magnet, the filings rust and stain the paint.  The coax rubs on the paint from wind turbulence, scratching it into a haze.  The door/window seal becomes distorted where the coax enters the vehicle causing wind noise, and during rain the water will run down the coax into the vehicle.  The coax becomes pinched at this point and eventually fails.  Mag mounts are great for *temporary* operation, say a rental car or to put an extra antenna on during a trip or whatever.  I keep a couple in my go-kit for ARES deployments, they're handy to have.  But I would never have one on a car on a permanent or semi-permanent basis.

Trunk lip mounts are a little better, but I still don't like them.  The setscrews pierce the paint inviting corrosion unless you take pains to minimize that.  Depending on the edge it's fastened to and the size of the antenna, there is a potential for the mount to stress the metal and crease it.  There is still the coax and trunk/door seal crush/deform/leak issues.  A minor nit is at the edge of a door/trunk lid it's usually not the best place to put an antenna performance-wise.

Many people shudder at the thought of a 3/4" hole in the roof or trunk of their vehicles.  Probably because it's the 2nd most expensive item they've ever purchased in their lives and think of the hole as irreparable damage, rather than the enhancement it really is.  The largest damage you incur to any vehicle is driving it off the dealer's lot, which amounts to thousands in depreciation.  At trade-in/sale time,  there isn't a dealer in the country that will deduct for an antenna hole.  People drill holes in their cars for all sorts of things, from cell phone and satellite radio antennas to accessory lights, mirrors and trim/ground effect kits.  A permanently mounted antenna works best, won't rust and won't cause peripheral damage.  About the only time I wouldn't advocate it is on antique or collector cars, but that's not what most of us drive.  So why not make your daily driver a good place to operate your radio from too.  All of these temporary mounts are false economy because they're not as long-lived and cost more than permanent mounts.  When I put an NMO mount on a car, it's there and working until the last day I own the car.  I just leave the mount behind and buy new ones for the next car.  It's not often in life the cheapest solution is the best, but this is one of them.  There are tools and techniques that make this task simple, and if you don't feel like acquiring them it's worth the $50 or whatever to have a professional install shop do it for you.  I've seen enough buggered up vehicles caused by temporary mounts to have come to these conclusions.  Just trying to pass this info on to the next generation of hams to save them learning this the hard way.

Mark K5LXP
Albuquerque, NM

Posts: 2080

« Reply #18 on: November 14, 2005, 10:18:46 AM »

Well, these folks all know that I am a huge "drill the hole" advocate too.

But, if you are not going to drill a hole under any circumstances, at least use an existing, factory-made hole.

Sti-Co makes VHF/UHF two-way radio antennas that replace your vehicle's factory AM/FM broadcast antenna.  (same hole)

Cool stuff!

Terry, WØFM

Posts: 17

« Reply #19 on: November 16, 2005, 07:42:47 PM »

Thanks Terry

But I like my car stereo so I need my antenna

Also, I just use my radio to hit repeaters and it does this just fine with a mag mount

In fact just the other day I hit a repeater about 52 miles north of me and had a pleasant conversation with the person until I got to my home another 7 miles south with no problems what so ever.

So, The mag mount will do just fine, no need to drill a hole in a prfictly good car to access repeaters


Posts: 7


« Reply #20 on: November 30, 2005, 06:35:08 AM »

1. Yes, drilling a hole in the best way to go. I've never had corrosion problems from a good *commercial* installation, and I generally put 120,000 miles on my cars, so resale is a non-issue. But it's not always possible- like on the Saturns I owned. Plastic makes a poor ground plane ;-) And some people just don't want to drill a hole.

2. Mag mounts are fine if you understand the drawbacks. Yes, there's a good chance of scratching paint, but if you leave it in place, and aren't constantly removing it, the chance is lessened.  A small 1/4 wave magmount will get you into a repeater in most urban areas. It's the massive super-magnet ones that can cause a lot of the big problems.

3. Trunk lip mounts can work very well, too. For VHF/UHF, using a ground independant antenna (like a 1/2 wave antenna) means you can operate without additional ground strapping or breaking through the paint. For HF, add ground straps and coat the area with a rust preventative- primer, regular shots of Boesheild, whatever.

Which way is best? The way that gets you on the air.
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