Thanks fellas! So now for the technical questions. I have done some digging in here to research these topics, but it's kind of like reading something in Spanish. I'm totally new to this stuff so go easy on me. I may have follow ups to some of these answers to better understand the lingo.
1.What does NMO stand for and are there other acronyms for antenna bases to watch out for? I think I saw a few more while looking and have no idea what is what.
New Motorola is what NMO stands for. It's the most popular type of professional mobile antenna mount. Tried and true in just about every single application. Installed properly, they'll outlast the vehicle.
NMOHF is a higher frequency model that's designed for GPS and higher frequency use. They are cross compatible with standard NMO's. You don't need one of these.
LM Mount. It's a stud mount. Falling out of favor. They'll work fine, but not quite the selection of antennas that you'd get with the NMO.
Stay away from SO-239/UHF mounts. They are somewhat popular amongst amateur radio operators. They are weak and not inherently waterproof. Often won't stand up to the beating of real world use, especially off road. Limited selection of antennas. Stay away from these, no matter what the amateur radio operators say. Not suitable for your use.
3/8x24 mount. Common with CB radio antennas. These are suitable for some types of antennas, but again, not a good choice.
Stay away from anything proprietary. NMO mount is the way to go.
Stick with the known good brands, Larsen, Antennex, Comtelco, etc.
Stay away from anything with the Browning or Tram name on it. They are Chinese knockoffs that have bought the rights to an old USA based CB radio manufacturer from the 60's.
2.What is a ground plane and how does it effect the performance?
It's basically the other half of the antenna. Many antenna designs require two parts: The radiating element and the radials or ground plane. Pickup truck cab roof is an excellent ground plane -IF- you mount the antenna right in the center. Ideally you want ground plane extending out equally in all directions under the antenna. This is why you'll see police cars with the antenna mounted in the center of the roof or trunk. Mounting the antenna off to one side, like a fender mount, causes some directionality to the antenna installation. Might work in your favor if the truck is pointed in the right direction. Won't help if it isn't. Center of a large metal plane is best. Doing -anything- other than this is compromising your system.
Only exception is non-ground plane dependent antennas. Basically a 1/2 wave design. They'll work OK without a ground plane, but they work much better with one. Don't use a 1/2 wave design and think you are getting something for free. You ain't.
3. Would a mag mount be ok since the mobile radios are only going in the chase vehicles that will be on the highway. Might have to go a couple hundred feet off the highway to a pit every now and again, but we aren't busting *** through the desert and dropping in holes. I definitely don't want to do permanent because I will be taking this off my personal truck and putting in on someone else's truck for the trip. I would like to be able to swap it over to the next truck in under an hour.
They are OK if you place them in the center of the roof. There is a small reduction in performance with magnetic mounts. The bigger issue is that you'll run the coaxial cable through a window or door, and this will eventually cause damage to it. This damaged coaxial cable, either pinched, crushed, cut or otherwise damaged, will cause at best impaired performance. At worst it'll damage your mobile radio.
I only use magnetic mounts for testing purposes or very short term installs. It is not a good solution in any sense of the term.
A good NMO magnetic mount will cost $40 or more. You can purchase several NMO permanent mounts for that cost. Magnetic mounts are not a cost savings. They are a quick and dirty solution for a temporary problem. They are also a half-assed solution for guys who's wives won't let them drill a hole in her mini-van.
Don't be that guy. The "but it's a leased vehicle" argument doesn't hold up. I've installed many NMO mounts on lease vehicle and never once had a problem at the end of the lease.
Yeah, they'll work, but you will get better performance from a properly installed antenna. You wouldn't run the Baja race with an old lawn mower engine in place of a real built motorcycle engine. Why do the same with your communications system?
4. Do they have mounts that clip in a door sill kind of like a roof rack clip and would they be better then a mag mount? Would it really end up being the same performance in the end because you can't locate it in the center of the roof?
Yes, there are mounts like this. You'll find them in the amateur radio catalogs next to the magnetic mounts. They are intended for the guys who's wives won't let them install a real antenna on her mini van.
The issue with these is they rarely make a good ground connection to the vehicle. At best they result in a lopsided ground plane under the antenna. Then they still have the draw backs of trying to get the coaxial cable into the vehicle through the door or window. Basically if you are using these, you should probably turn in your "man-card". They'll work, but work poorly, plus others will point and laugh. No seriously, no one should be laughing, but if you are going to do a half way install like this, at least go with the magnetic mount and put it in the center of the roof.
5. How would one go about tuning for 151Mhz like said above and in everyone's opinion, will tuning be necessary in my situation? I want to do this right, but I will not have any special equipment to measure performance.
To do it correctly you either need an SWR meter or a return loss bridge and some other equipment. The SWR meter is the cheapest solution, but you are still looking at >$70 for a half way good one. It's a good investment if you are going to be serious about this. Should be one of the first tools you purchase. Tuning your antenna properly will make a big difference in performance. Not tuning an antenna is doing a halfway install.
On the flip side, antenna designs like 1/4 waves are pretty broad banded by nature. You can often cut them using the included cut chart that comes from the manufacturer and get "close enough". Being off by an 1/8 inch or so isn't the end of the world. Still, I always put mine on my analyzer to make sure. Checking the entire install with the right test gear will help find any hidden issues that you might miss, including issues with connectors, corrosion or damaged coaxial cable.
6. Why do the permanent mounts outperform the mag mounts?
Proper connection to the vehicle ground. Mag mounts make this connection by using capacitive coupling. It works well enough when dealing with RF. Jumping the gap between the magnet base, through the paint and too the roof does pretty well. There is a very slight amount of loss. Truth is it would take some specialized test gear to see this minimal amount of loss.
The benefit to a permanent mount is that it looks professional. It'll work better. It'll prevent damage to the paint. It'll prevent damage to the coax. It'll tell the world that you value radio performance and professionalism. It'll also tell the world that you retained your "man card" and your wife doesn't get to call all the shots (but still most of them).
7.Would having a tall 49" replacement whip be better then a 18.5" whip on a spring? Height will be no issues because there will be nothing to catch the antenna like trees and such. Just Cacti, but they won't go over the truck.
Antenna length depends on the frequencies being use and the type of antenna design. You can't just swap out whips and expect the system to work correctly. A quarter wave antenna on VHF will be about 18 inches or so. If you change that length you are changing the characteristic resonance of the antenna, basically making it work on a different frequency.
If you want a lower antenna, stick with the 1/4 wave design.
If you want a longer antenna, look at a 1/2 wave or 5/8 wave. They require coils at the bottom of the antenna to make them tune up correctly.
The 1/2 wave and 5/8 wave antennas will give you more gain, basically focusing more of the RF energy down towards the horizon. This effectively increases the overall system RF output. It works well in lots of flat terrain, but it can be a hindrance in the mountains. Likely you wouldn't be able to tell the difference. A 5/8th's wave antenna design might work a bit better for you guys for what you are doing and the locations.
8. Do some types of mag mounts out perform others and why?
They all sort of suck. A bigger diameter base will couple a bit better to the ground plane under the antenna. Using really small bases probably doesn't work as well. Also, the bigger magnet will give you more holding power. It'll also damage a bigger area of paint on the roof. Mag mounts are notorious for leaving scratches on the roof. Dust gets under them and can do damage. Since you'll basically be swimming in dust down there, I'd make sure you are comfortable with some scratches on the roof of your truck.
9. What is antenna gain and why is it important?
Antenna gain is basically the design of the antenna focusing more power in certain directions. For mobile antennas, the antenna design will determine the amount of gain. By comparison, a 1/4 wave antenna is considered to have zero gain. A half wave antenna with no ground plane will also have zero gain. A half wave antenna with a ground plane will have about 2.4dBd gain. A 5/8ths wave antenna will have about 3dBd of gain. For ever 3dB of gain, you are effectively increasing the radiated RF energy by 2 fold. This is done by focusing more of the RF energy at the horizon, rather than in a more circular shape as a quarter wave would have.
Think of a light house. A 1000 watt incandescent light bulb is pretty bright, but from 15 miles away it's going to be hard to see. Now use a mirror behind it and lenses in front of it to focus the light into one direction. Suddenly that dim 1000 watt light bulb 15 miles away is brighter. Draw back is that the area actually lit by the lamp is decreased. Not an issue if the people you are trying to shine the light at (talk to with your radio) are on the horizon. If they are well above or well below the horizon, it's not going to work so well.
This is one of the reasons why a quarter wave antenna will often outperform a higher gain antenna in high mountains.
For where you guys are going to be and what you are doing, a 5/8ths wave antenna might work better. It'll sacrifice bandwidth, but will probably work a bit better. Since you want one antenna for for amateur radio and commercial/race use, you might be limiting yourself. 2 separate antennas that you swap out depending on your needs would solve this. One tuned for 2 meter amateur use, one tuned for your race frequencies.
A half wave antenna is sort of a good compromise. It'll probably work well on amateur and the lower frequency commercial stuff while still providing some gain.
A quarter wave will give you the bandwidth to do commercial/race stuff as well as amateur radio use in one antenna.
Over the years I've tried many different antenna designs, and I really don't hear a difference. I've stuck with quarter wave antennas since they serve my needs best. I can have one antenna for amateur radio use as well as the work/commercial stuff I do. I've tried 5/8ths wave antennas and they work well, but the additional length is a problem for a full size truck in a suburban area.
Where I have had luck is mounting 1/2 wave antennas on a Polaris Ranger roll cage. Since the roll cage doesn't supply a very good ground plane, I've seen slightly better performance by using this antenna type.
As they always say, your milage may vary.....
10. Is the higher the gain the better? Like is a 3db better then a 2.5db? Can you get an antenna for my situation that is higher than 3db gain?
Depends on what you mean by "better". For my own personal use (see above) a quarter wave antenna is "best" for me. Someone who sticks to the 2 meter amateur frequencies and not need to transmit anywhere else or they live out on the plains might say a 5/8ths wave is "better".
The difference between 2.5dB and 3dB is probably something you wouldn't be able to hear with your ears. Would take some test equipment to see the difference. On the other hand, that 0.5dB might make an unreadable signal slightly better, maybe enough to make out a few words. It likely isn't going to be a night and day difference. Chasing fractions of a dB like this can get costly and usually doesn't pay off well enough to be worth it (in most cases). If you are really wanting to chase down every little bit of signal you can, skip the magnetic/bracket mounts and do a proper installation. The better ground plane and safer cable routing will probably pay off more. Adding a higher gain antenna would add to that improvement. Staring with a poor antenna mount and trying to make up the loss in performance by adding bigger antennas is probably not going to pay off too well.
Hey, if you really want to thank us, -PHOTOS- of the set up when you are done. Bonus points for photos from Baja! We'd probably even reinstate your "man-card" if you did a magnetic mount AND won the Baja for your class.