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Author Topic: New Ham/LOTS of antenna questions!  (Read 4043 times)
KF5GDA
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« on: April 19, 2010, 02:43:22 PM »

Brand new Ham here...and really needing help.  I've been staying up past 3am every night for several weeks trying to learn on my own, but the antenna has me stumped!

Thru HOURS of research, I have decided on a Kenwood TM-V71A (2 meter and 70cm) for install in my 2007 Xterra.  Where I really need help is with the antenna.

I will NOT drill a hole in the roof.  A mag mount is my fall back plan, but I want the best setup I can get.

Questions:
1.  My Xterra is already 6'7".  I am concerned with hitting drive thru windows overhangs, parking garages, etc.  Do they make Ham mobile antennas with a spring mount like CB antennas?

2.  I am totally baffeled by grounding antennas.  Some antennas say, "Can not be used with Mag mount".  If it does not specifically say that, does that mean it CAN be used on a Mag mount?

3.  My Xterra has a factory roof rack.  Can I remove the bolts from one of the corners, fabricate a bracket and use a longer bolt to go thru both the bracket and roof rack?  If I then mount the antenna to that bracket, would it be properly setup/grounded?

4.  If I buy a metal roof light rack that bolts to the roof, can I mount the antenna to the light rack using one of the mounting tabs on the rack?

5.  Is going thru all this hassle worth it?  In the REAL WORLD, how much extra range will I get by fabricating up a mount instead of just using a mag mount with the same antenna???

I am currently looking at the Diamond MR77 (19.5") for use around town, then when I am going to be in the boonies, unscrewing that antenna and switching to the Diamond SG7500A (40.5").  Can I do this?  Will the antenna unscrew from the MR77 mount, and will the SG7500A screw into the mount?  So, whatever mounting system I use must be one where I can easily change them out.
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K0BG
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« Reply #1 on: April 19, 2010, 04:02:42 PM »

Perhaps a visit to my web site is in order. http://www.k0bg.com

When you limit yourself to not drilling holes, you're already at a great disadvantage. Yes, mag mounts 'work' to some extent, as do glass mounts, and other no-hole antennas. HOwever, you, and you alone, need to decide just how little (or how much) coverage you need. Just remember, my opinion of what the word 'works' means, and others, isn't the same!
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KE4DRN
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« Reply #2 on: April 19, 2010, 06:26:19 PM »

hi Jeffrey,

K0BG website will give you several options.

the diamond MR77 and SG7500A mounts are not interchangeable.

consider the NMO type mount with a
Larsen  NMO 2/70B  antenna.

http://www.eham.net/reviews/detail/434

you will only have to purchase one antenna and mount.

73 james
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KF5GDA
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« Reply #3 on: April 19, 2010, 09:04:36 PM »

So, unless I am willing to drill a hole in my roof, nothing else is better than a Mag mount?

If I fabricate a bracket that I bolt to the roof using existing holes, and mount the antenna to a hole I drill in the bracket, would that work better than a Mag mount?

Finally, which is the better mount type, NMO or UHF (SO-239)?

I did read a LOT of the articles on your web site.  I admit, some of it is over my head.  You are very clear there that you really feel drilling a hole in the roof is the way to go, but that is not an option I'm willing to do.  I'm just not hardcore enough either to spend $1,200 on an antenna as you mentioned on your site.  However, my wife and I do find ourselves in very remote locations during disaster response, and I would like to have as much range as I can get without drilling 1/2" holes in my trucks roof.
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KC7YSF
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« Reply #4 on: April 20, 2010, 02:24:39 AM »

I was faced with the same dilemma that you are facing.  I did not want to drill into the roof of my truck either.  I was able to attach a steel bar across my metal tie downs in the bed.  I had another bar welded vertically so that it was just slightly higher than the roof of the cab.  I placed my antenna on top of this bar.  It has been fine for my uses.  Additionally, I have from time to time placed mag mounts on top of this frame, to use other antennas on a temporary basis.  Surprisingly, I do not find the performance of the mag mounts to be inferior to the mount I drilled into the top of this frame.  

Many of the people on sites such as this are contest competitors and they want to get the last fraction of a percent of performance out of their systems.  Most of us do not need this degree of performance to use our radios in an acceptable manner.  My advice is to experiment with a mag mount and see if you can get the performance to need to areas that you might likely visit during emergencies.  A mag mount is always valuable to have in your "go bag" even if you end up using another mount on your truck.  

Most of my friends use NMO mounts.  So do I, and I have found them to be perfectly reliable.
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K5LXP
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« Reply #5 on: April 20, 2010, 06:47:59 AM »

NMO mounts are a commercial standard, in use since at least the early '70's, if not longer.  Whatever scheme you end up deciding on (mag, angle bracket, custom, et al) by all means pick one that utilizes an NMO mount.  By doing that you'll have a very mechanically and electrically sound, durable, and universally compatible system.  You can get just about any antenna made by any manufacturer in an NMO version.  Not so for other types of mounts.

The reason you'll find emphatic supporters of hole drilling is that it solves several problems at once.  It's fast, easy, inexpensive, the most durable and the best performing.  How often do you encounter a situation like that?  You will learn (the hard way) that temporary and compromise mounts are more time consuming and expensive to install, aren't as durable, more prone to problems and can actually damage the surfaces of the vehicle more than a small hole will.

The greatest devaluation you'll do to your vehicle short of having a wreck is driving it off the dealers' lot.  People poke holes in their cars for all sorts of reasons and done right, does not detract from value.  Cars aren't investements anyway.  I consider it an enhancement to value.  It's my hamshack on wheels that gives me entertainment and safety- why not get the most out of it?

I would offer one other suggestion, and that would be instead of a large dual band antenna on the roof, go with a smaller "lower gain" model that has a thin element.  Antennas like this are nearly indestructable and do not rely on a spring or a folding mount for low clearance situations.  It won't stress the mount either.  This would solve your rooftop clearance concern.


Mark K5LXP
Albuquerque, NM
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WX7G
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« Reply #6 on: April 20, 2010, 07:14:36 AM »

I would start with a mag mount and see how I liked it. You can have fun upgrading the antenna as time goes by.

http://www.firestik.com/Tech_Docs/roofrack.htm

An article on roof rack mounting of antennas.
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WB5JEO
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« Reply #7 on: April 20, 2010, 07:57:22 AM »

Given that you don't want to drill the roof, I think your main concern is going to be establishing a good ground absolutely as close as possible to the base of the antenna. Every antenna you will consider depends heavily on a good ground plane of some sort. Longer ground leads from the base to the body pervert the antenna design by essentially adding another (grounded) "element." Obviously, this can be reasonably well done using your option of using the roof rack mounting hardware, but it will take some thoughtful attention to the ground. They weren't thinking of that when they designed the rack mounting, and you will need to look at how they did it. They were likely thinking of two issues at the factory. One was making it efficient in terms of assembly. The other was not allowing a point where rust was likely to get started. If you're mounting a bracket or whatever on top of the rack footing, the bolt or screw may not make much of an electrical connection where it holds to the body or to whatever nut-like device is under there to receive it, which may not be conductive at all. It may take some maneuvering to establish a good connection. "Star" washers can help, because they take a bite on the metal. You'll see more what you're dealing with when you get the rack off, which I think you'll have to do to see what it's screwed to.

The roof light rack presents the same problems. For that matter, if you're prepared to mount a light rack by drilling, might as well drill for the antenna.

Antenna are, of course, best mounted high and centered, but a lot of that is nicety. I'm not a big fan of unscrewing and changing antennas. It's way too easy to lose one if it's not real tight. I would serious try the smaller antenna first. It (actually one for permanent mounting, rather than mag mount) may well do everything you want to do. The difference between the antennas isn't going to be striking and may not be detectable in real use. The small one will survive the garage ceiling strikes okay. If you feel it lacks in fringe areas, you can always reconsider. I've never done anything like critical testing, but I've used many, many VHF and UHF radios with simple quarter-wave "pimp stick" antennas and hit repeaters at any distance I'd care to and expect to. Consider that in a typical situation of your antenna at six feet and the repeater antenna at 100 feet, the line of sight distance is maybe 15 miles. Obviously, the repeater range is almost always greater, but it gives you the idea that there is a limit to reasonable expectations for line-of-sight communication. What are your "boonies?" If that's at a high elevation, maybe you don't need any more antenna. Or maybe for your boonies, it's going to take more than even the big vertical. You just have to try it.

Will any of this matter enough to make you a real difference? Who knows? You might find the mag mount works for you everywhere you want it to. In absolute terms, it's clearly a lesser installation. But if a lesser installation works, it works. None of the antennas and mounts are so expensive that you'd feel real bad if one wasn't quite what you wanted and was relegated to something like temporary mount in a second car of sold off to someone at a discount.

My bottom line gut feeling is that, unless you're going for distinctly longer distances to repeaters, it will all work, and if you're anticipating something like working from a camp site at or beyond the fringe, carry simple Yagi's and mast on the camping trip.
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KF4HVX
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« Reply #8 on: April 20, 2010, 08:22:36 AM »

If you are concerned about hitting overhangs there are mounts out there that are motorized to tilt your antenna down.

I have seen one advertised in HRO's catalog but I am sure they are available at the other ham radio equipment providers.

With this as a mounting option you can mount a variety of the antennas mentions in this thread.

Personally, I use a small dual band mag mount. Around town it works fine. It does not have the ability to get out like my 5/8 mag mount did.
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WB5JEO
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« Reply #9 on: April 20, 2010, 03:55:53 PM »

The motorized folding mounts I've see specify ground-independent antennas. Kind of limits their applications.
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KF5GDA
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« Reply #10 on: April 21, 2010, 01:01:03 AM »

Thank you to everyone who replied.  Each post has helped me.

My biggest concern about doing a NMO thru the roof mount has to do with rust.  Since the mount needs bare metal, what do you do to keep it from becoming a big rust problem???

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W5LZ
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« Reply #11 on: April 21, 2010, 04:03:10 AM »

Jeff,
While rust is certainly a possibility, it's not the most likely one.  I honestly wouldn't worry about it a lotif you do the installation correctly.  Most mounts furnish some means of sealing, a gasket typically.  Want to seal it a bit more?  Then use some 'grease' type substance that's not conductive, and be careful about -where- you apply it.  It shouldn't take much at all.

Drilling that hole is almost always a better idea.  Mag-mounts are fine, IF, they are absolutely necessary.  Not a matter of 'wanting' to drill that hole, but "can't" drill that hole for some reason.  Mag-mounts do have limits though, and are always a compromise of some sort.

Other kinds of mounts are also 'usable'.  I'm sure you've seen the typical 'hood'/'trunk' mounting bracket that attaches under that 'lid' where the holes don't show.  They work.  One very good idea is to keep that 'bracket' as 'short' as possible.  The 'taller' ones can introduce 'matching' problems.

And the same old story, the 'bigger' antennas are usually better for 'range'.  That's because they typically have some 'gain' to them.  Just don't expect 'miracles' with all that 'gain' that's advertised.  VHF/UHF is more a 'line of sight' thingy, and long ranges are not that common.  Lot's of "fudge" in that, you'll see as you gain experience.

About drilling those 'holes'.  It's done all the time, NOT as big a deal as most people think.  When it's time to trade that 'hoopy' in on another and the salesman/dealer makes a big production out of that hole, say thank you and leave.  Bet'cha you don't get 10 feet before they change their 'tune'.  (That's the hole where the cell phone or GPS antenna goes, don't'cha know?)
Paul
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K0UA
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« Reply #12 on: April 21, 2010, 02:43:51 PM »

NMO is the way to go, and Larsen is the best.  I use the 2/70 on a NMO bracket mount on my silverado. and have for several trucks.  Car is a 2 meter only using a NMO 1/4 wave on a angle bracket at the trunk.  I have drilled Hundreds of holes in cars (I used to install commercial radio for a living).  lots of the 3/4 holes for the NMO  and they don't leak or rust. If you are worried about rust you could use a little grease on the raw edge of the hole, applied with a rag or something not your finger (ouch). I use NO-Ox_Id for all my drilled holes now( google it). Yes hole mount on roof is best, but fender mount with the angle bracket works well. You still have to drill 3 little holes for the screws, but they cant be seen.  You have to ask yourself, what is on a police car.? is it a Diamond, no probably a Larsen.  Everybody has opinions, you have to find what works best for you. I hope I have helped not hurt.
73
Jim K0UA
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KC7YRA
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« Reply #13 on: April 24, 2010, 08:38:05 AM »

Not to jump on the bandwagon, but add a +1 to the "drilling" crowd.

For years, I ran magmount antennas on my truck.  From HF thru 70CM, I looked like a porcupine.  I would run the coaxes through doors and windows which would lead to leaks and horrible wind noise.  I also had to replace coax CONSTANTLY as I was always chopping it.  And forget 4 wheeling or driving into a severe headwind.  Nothing like having 5 magmounts fall off at exactly the same time.  Scratching the paint and falling all over.  It was  real mess.  And you think one of those 3 or 4 magnet jobs will get it done?  I still possess (as a reminder) a 3 magnet mount that I had an antenna on when I got into a wreck.  The magnets stayed with the vehicle, but the mount didn't.  The coax snapped and the entire contraption flew off my truck with great force.  the LAST magmount I ever used.

I finally decided to drill.  I was working at a radio shop and had done hundreds on customer vehicles.  And I had seen how well they lasted on the 20 year old installs that would come in.  Installed properly, NMOs do NOT leak and never will.  They are extremely reliable and universal.  A proven design that has lasted for decades and will last many more.

My current "main" vehicle is a 2001 F-150.  2 hours after I bought it NEW, I drove it into the install bay and punched 4 holes in the roof and a number of them in the bed, for the HF antenna.  All of them 3/4 inch or bigger.  Did I de-value the new truck?  Yes, at that time.  But here I am almost 10 years later, 100K+ miles on the truck.  The trucks value at this point has NOTHING to do with any holes it may have.  Trade in is the same if it had no holes or I added 10 more. 

And over those past 10 years, I have had ZERO leaks, problems, or significant failures.  I put quality NMO mounts in and Larsen antennas on.  Everything is as good as it was the day I put them on.  Try that with a magmount and see what your point looks like under it.  It will look a LOT worse than if it has a small hole.  Plus, the difference is noticeable.  Properly mounted antennas have always performed better in my experience. 

With all of the benefits of the NMO and all of the negatives of the magmount, please give the drilling a serious thought.  It is scary at first, but worth it.  Besides, you don't buy a vehicle as an investment do you? 

Brad
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KF5GDA
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« Reply #14 on: May 04, 2010, 03:28:26 PM »

I have continued reading, trying to learn....Please, feel free to correct where I am wrong.

My understanding is....A 1/4 wave antenna REQUIRES grounding, so you would HAVE to do a thru roof NMO mount.  A 5/8 antenna NEEDS to be grounded with a NMO thru roof mount (but is not required).  A 5/8 wave antenna is the best for ultimate gain.  If you are mounting on the bumper or a magnetic mount, you use a 1/2 wave antenna.

My question is....When looking at a dual band antenna at http://www.rfparts.com/diamond/Product_Catalog/mobile.html
I don't understand what antennas are 1/4 wave and 5/8 wave and 1/2 wave.  Is it the column named "Element Phasing/Wavelength"?  If so, what does 2 5/8 mean?  Is the SG7500 both a 5/8 AND 1/2 wave antenna?!

I admit, I'm really tired of being confused....Thanks for all help guys...
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