Lots of good information, lots of bad information, lots of ignorance (I don't mean that in an insulting manner - I've got a lot of ignorance here too).
There's a lot to unpack here. I feed my GMC Jimmy project with a two-way radio job, so.. might as well help.
Rugged Radios - HUGE problem here. I hate them, they are selling product that is very often illegal, very often intended to be used illegally but not advertised as such (think 'oil filter' silencers, etc etc). The radios aren't terribly good. BUT. They are the best option readily and cheaply available. The GMRS frequencies require an individual license, but that is cheap and easy.
GMRS FRS PRS CB HAM NBC CIA VHS EFI -
https://www.fcc.gov/consumers/guides/personal-radio-services-prs-keeping-touch There are a mess of different 'services', or ways you can legally transmit on a specific frequency or set of frequencies. GMRS permits 50 watts of transmitter power in the UHF 'band' (notionally anything between 400 and 500 mhz or so).
MURS is VHF (130 - 180 or so), but limited to 2 watts.
CB is AM only, limited to 12 watts in SSB mode and 4 watts normally in "Low Band" (26-27mhz).
AM - amplitude modulation. You can play with the different characteristics between AM and FM audio in a VERY LIMITED sense using your car radio. Please note that AM 'goes further' more because of the frequency than the nature of the thing. A more accurate comparison will be aircraft radios (AM in 108 - 137mhz range) vs GMRS channel 1 (462.5625 20khz 'wide' analog FM) vs FRS channel 1 (462.5625 12.5khz 'narrow' analog FM).
FM - Frequency Modulation. Where an AM radio can interpert tiny changes in signal level as noise (because the Amplitude or level of signal is where the voice audio data is encoded), FM ignores those changes. In practice, Steely Dan almost had it right - no static at all! FM also lets us play with channel width (as seen above). The 'wider' a channel, the less of them you can cram into the same frequency range. Think of King of Hammers, if everyone had two or three channels available to them, total. However, the wider a channel, the more voice data you can put into it and the better it sounds - AND the better it 'carries'.
VHF UHF Lo Band - radio frequencies exist on a spectrum, just like light. In fact, light is also part of the radio frequency spectrum. This is important because two radios have to be setup on the same frequency to talk to each other, and a VHF radio generally will not tune to UHF channels. To break it down, your Alpine in your daily driver will recieve transmissions from 88.1 MHz to 107.9 MHz (Megahertz), which gives you a good foothold in where RF stuff lives.
This bonkers complicated and almost useless PDF lists who goes where in more detail, if it doesn't crash your computer.
It's also important because different bands act differently.
CB, at 26 mhz, will 'terrain follow', bending to some extent over hills and around corners. It will also 'skip', or bounce off of parts of the atmosphere to cover colossal distances. My father had a cabin in the mountains in Alaska and would key up on CB to yell profanity at the mexican truckers he was hearing - sometimes they would yell back. Yes, the old man worked skip from Alaska to Mexico. Unfortunately, the 'fundamental length' of a CB antenna is 516 inches for a 'full' wave - not at all useful. Means a lot of compromises in antenna design to get something that can go on a rig.
VHF will terrain follow to a lot lesser extent than CB, almost never skips (it's theoretically possible, but I've never seen it IRL). VHF shines because it cruises _through_ a lot of trees and foliage and ground scrub, making it very useful IRL. The fundamental length of a VHF antenna at 151.8mhz is just about 72 inches, making the compromises in design a lot less and the antenna performance a lot better.
UHF pretty much doesn't terrain follow, and starts having problems with Green Obstacles (trees and brush). However, the fundamental length is great, at 462.5625 we're looking at just a hair over 2' for a full wave antenna!
1/2 wave, Full wave? - I talked about fundamental length earlier, that's the actual size an antenna needs to be to 'capture' the entire RF wave at a given frequency. At CB frequencies especially that's a HUGE chunk of wire. So to make a physical antenna that you buy easier to handle, we make design compromises and use a "1/2 wave" or "5/8 wave" or "1/4 wave", which are 1/2, 5/8, or 1/4 the length of the notional 'full wave' antenna. Rule of thumb is that the 1/2 wave works about twice as good as a 1/4 wave, and a 5/8 is just a little better than the 1/2 wave, but trades bandwidth (just squinting at GMRS I don't think we care about bandwidth - in this context it means multiple channels, not the 20/12.5 for any given channel).
Conclusion - the most common problems I've ever seen in two way installs (taxis, ambulances, cop cars, pilot cars, trailers, off road rigs, hand held radios, amateur radios) are NOT 1/4 wave vs 1/2 wave or using the 'wrong' band (VHF vs UHF). You're gonna have the most problems because of the following
- Power. A 50w mobile needs around 5 amps of current at full booyah. Motorola, as the 'gold standard' ships a 12 gauge wiring harness for power with their 50w radio that they tell you to connect directly to the battery. So don't run 18 gauge or plug the thing into the cigarette lighter through a 30' extension or land the ground on a self tapping screw into body steel. Run 12 gauge to a good power distribution block and a good ground, fuse at 15 amps and win.
- Physical. All the radio in the world doesn't matter if you can't hear it. Many folks don't put any thought to this and end up with the tiny little 3/4" speaker in the radio trying to overcome 650 horses worth of V8 and tons of watts of stereo and and and.. it don't work. Get the external speaker, and put the thing up where it's not hidden away. I like the ones that mount the external speaker on the back side of the driver's b pillar angled forward, pointing it directly at the driver's ear.
- Antenna. You really need a strong connection to an antenna that is the highest point on the vehicle for best performance. Rugged looks like they ship standard NMO mounts, which want a 3/4" hole in roof steel - these SHOULD have an o ring and a rubber gasket. DON'T CAULK THEM. Put some dielectric grease on the everything when you assemble and she'll be right. Mag mounts SHOULD have a plastic bottom layer and go onto roof steel. Wipe the plastic clean to get rid of chunks or dust, wipe the roof clean, thonk. Your roof needs to be bonded to ground at some point.
If you're putting the antenna on a mast or bracket on the roll cage or something, so long as the steel is grounded and the antenna is at or near the highest point, life is good.
Handhelds - The biggest problem I've seen in handhelds is that the poor radio is trying to get it's signal through 250 pounds of meat because it's on someone's hip, or it's in the cup holder of a solid steel box (like, for example, most times I use a handheld). It APPEARS that most of the rugged radio handhelds use a BNC female connector on the radio, so if you're gonna be using it in a vehicle, you can absolutely and SHOULD absolutely put a magmount antenna on the vehicle and (without crushing the cable) run it inside and plug it into the hand held. 4w is less than 50w, but getting the antenna outside the grounded steel box is HUGE. Getting that extra 4' of height also helps.
Antennas - If your antenna doesn't have a cut chart to cut it to the correct length for your 'center frequency' (the center of your normal frequencies - as your frequency gets further away from this center frequency, the performance gets worse), you need to either hit up the manufacturer, or get a watt meter and start figuring. 465.14375 is the center of GMRS
If your antenna just got smeared off by an overhang or a garage door, could I interest you in
https://sti-co.com/project/flexi-whip-antennas/ instead? 7" of pokey pokey flexible enough to smear completely over in about 1" of length without breaking, and sturdy enough to do it for years. My favorite use of these is on underground haul trucks in a gold mine - they just bend over and laugh when the truck smears a corner underground, where anything 'normal' was shredding mag mounts and getting broken.
and the big problem.. Everyone in your crew has to be on the same frequency and same transmission type (AM vs FM, Analog vs Digital) to talk to each other. Test that before you roll out, charge your batteries, and keep your antennas overhead.
