Can someone explain GMRS vs CB, and the benefits of a fixed mount vs handheld?

[pablo94sc]

I'm not new to off roading, but I am new to off roading in the middle of nowhere. So I've done a little research on extra kit needed for that and was like, duh, a radio. So I'm seeing you guys installing GMRS radios in the cab, and thought that was a type of CB. Wrong! You need a license for them.

Now onto noob questions time!

1. What are the benefits of GMRS over CB?

2. Do I need a license for all GMRS radios, or just fixed mounts? Do you really need a license, or could you fudge it?

3. What's the benefit of fixed mount over a handheld? Is it wattage (range)? Wouldn't a handheld be better for situations where you might need elevation to get a broadcast out?

I think that about covers it. Haha. Thanks!

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[CoryB]

1. GMRS has greater range than a CB, which can be very useful in backwoods situations. It’s still nowhere near as long distance as Ham radio, but it’s better than CB.

2. I never saw any difference in licensing requirements between mounted vs handheld, but I never looked. The license is no big deal. Just fill out the application and submit it. I got mine a few years ago and it was free. I’ve never had anyone ask to see the license but it really is NBD to get it.

3. Fixed mount probably has better range due to the antenna size and using the vehicle as a ground reflector for the signal. Mounted is also a lot harder to lose when you’re going over rough terrain.

I come from the Jeep world and have attended a number of Jeep Jamborees. They changed their radio requirement to GMRS a few years ago, probably mostly for the range advantage.

 

[Bmadda]

GMRS=General mobile radio service. CB=citizens band radio. FRS=Family radio service. CB is AM. GMRS and FRS are FM. GMRS power is limited to 50 watts. FRS is limited to 2 watts. All FRS frequencies are part of GMRS, but power is restricted on FRS frequencies. GMRS HIGH power frequencies are GMRS only. A license is required for GMRS, but it is merely a formality...pay the fee and FCC will issue you a callsign. Your callsign is valid for family members as well...my son and I use GMRS all the time when driving separate vehicles, but if somebody asks our callsign, I announce mine, then explain his is the same or vice versa. The only time I generally use callsigns is when reaching out over a repeater, or if someone on our channel asks for it. Handhelds generally are low wattage (under 5), but they have drastically improved in recent years. they usually are fine for "line of sight" or if you are fairly close to a repeater. I keep a handheld in my glovebox...there are many inexpensive ones, and I have a mobile installed. Many mobile installs advertise the full 50 watt power, but testing has shown they often fall in the 40-45 watt range in reality.

For whatever reason the off road community has adopted GMRS...so if you are in a place where the only likely people you will contact are off road enthusiasts (Moab, Johnson valley, Rubicon etc) GMRS is the radio to have. There is alot of interest in GMRS from radio enthusiasts too, since the full HAM license isn't required. I used to enjoy CB in my younger years, and people abusing the airwaves made CB basically unusable. GMRS is better regulated, but it's not like the FCC has police out there...doubtful they really care. Lots more good info here https://mygmrs.com/

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[pablo94sc]

Good info. I'll probably get a handheld unit. While we will be going to some pretty remote places in the future where extra range would likely be needed in an emergency, I think I'd prefer the ability to carry it with us on hikes.

 

[Bmadda]

Good info. I'll probably get a handheld unit. While we will be going to some pretty remote places in the future where extra range would likely be needed in an emergency, I think I'd prefer the ability to carry it with us on hikes.

A decent handheld is a good buy, and even if you do a mobile later, it's handy to have in case you want a passenger to spot for you, or somebody gets out to walk ahead and scout the trail. Nice to be able to radio back to the vehicle instead of having to walk back!

 

[Alaska Steve]

I've worked in the radio field for 40+ yrs... I've mapped out link budgets for UHF, Communication Satellite, GPS, and cellular radio systems and have a deep understanding of antenna gain, power, transmission line loss, cascaded noise figures, noise figure, signal to noise, etc.

Here are a couple general topic links to learn a little bit about CB vs GMRS

CB and GMRS Comparison​

GMRS Licensing​

If you end up buying a mobile GMRS unit (which I recommend based on overall performance over CB), I highly recommend using LMR240 coaxial cable from Times Microwave as a low loss alternative to RG58 or RG6. You can get the cable from Field Components to your specified length - UHFM-LMR240-UHFM-[Length]FT and a variety of connector ends specific to your needs. You may need a NMO to PL259 adapter to attach to the antenna. You will have to buy the antenna separately; opt for a 6dB gain antenna (5/8 wavelength) - it's longer (32in), but it will more than double the power of the standard 2.5dB gain antenna that is less than half the size. When compared to the handheld, you will get 10x the power out of the radio plus an additional 4x (or close to 200W) out of the 6dB antenna.

Handheld radios usually have a 1/8 wavelength antenna. You can upgrade the antenna to 1/4 wavelength and double the range of the handheld without changing the power rating. Both will only give 2dB of antenna gain.

Understand dB (Decibels)

Bottom line... licensing is easy, I like the mounted unit better because it will work best in a remote environment. You can adjust many aspects of the mobile unit, including low/medium/high power output. Repeater access is good in most off-roading communities too.

 

[superj]

so, roughly how far is 40-50w of talking power? if you are in the desert or lightly treed areas? do trees even effect that stuff?

we had cbs in the jeeps a few years ago and where i live, you could get about 10-15 miles before you couldn't understand what was being said. i live on the coast though, on the gulf of mexico, so its flat and open

 

[Roverhound]

If you are going anywhere remote you should get your HAM license. Sure get a GMRS hand held to talk to your buddies you're with but if you're stuck in BFE a 2 meter rig is more likely to make contact with someone.

 

[BHunted1]

Get both.... I have cb and gmrs in truck... also have 2 gmrs handhelds when we go to the Smokies...
Amazon.com: Midland – MXT275 MicroMobile® GMRS Radio – 15 watts Two-Way Radio with Integrated Control Microphone – Overland Caravanning Tractors – Detachable External Magnetic Mount Antenna - 8 Repeater Channels : Electronics
Amazon.com: Cobra 75 All Road Wireless CB Radio + Cobra HGA 1500 Magnetic Mount CB Antenna : Electronics
Amazon.com: Midland - LXT600VP3 - Handheld Portable FRS Business Overlanding Gear Two Way Radio - Long Range Rechargeable Walkie Talkies for Adults - 121 Privacy Codes, Weather Radio - Black (2 Pack) : Midland: Electronics

 

[Bmadda]

so, roughly how far is 40-50w of talking power? if you are in the desert or lightly treed areas? do trees even effect that stuff?

we had cbs in the jeeps a few years ago and where i live, you could get about 10-15 miles before you couldn't understand what was being said. i live on the coast though, on the gulf of mexico, so its flat and open

Weather and terrain make a big difference. Being FM GMRS is mainly line of sight. We found in the Rockies and Moab that the signal will "bounce" off mountains and travel unexpected distances at times. Here in mostly flat, yet forested WI I can usually hit repeaters within 20 miles...25 in good weather. Using Midland MX575 w/6db antenna. Simplex I can't get anywhere near that distance reliably though. As vehicles move around in the terrain signal will come and go. In mountainous terrain the repeaters are even more effective I expect

 

[Alaska Steve]

So, I decided to use a simple online link budget calculator to see it what shows.
First I tried a fixed mobile unit with a 6dB antenna to a handheld unit with 2.5dB antenna. The radio manufactures don't tell you what the receiver sensitivity is but you can estimate that as the Noise Power in 20 KHz of bandwidth is -130dBm (accounts for the noise floor at -174dBm plus the bandwidth noise) and it's reasonable to expect a receiver Cascade Noise Figure 5dB and a signal to noise figure of 7dB, estimating the receiver sensitivity at -118dBm. That would be the point where nothing is intelligible. So add 10dB under perfect clear line of site plus another 10dB in moderate obstruction and you end up at -98dBm. Truthfully, most people use -95dBm as the standard minimum signal strength for sustainable communication and -85dBm preferred. So I'll stick with -95dBm for the examples, but wanted to show how I came up with that number.
So first example, fixed mobile unit with a 6dB antenna to a handheld unit with 2.5dB antenna:

Now, due to Earth curvature, you're never going to realize 90mi unless one of the units is on a hillside, so here is a more realistic example...

Compare that to a handheld to a handheld...

That's all theoretical. Your mileage may vary. I provided the link above if you want to play with numbers...

 

[Arsenall11]

We in the northwest are lucky, we have two repeaters gold and tiger, off the repeaters I average about 60 miles.

 

[pablo94sc]

So, I decided to use a simple online link budget calculator to see it what shows.
First I tried a fixed mobile unit with a 6dB antenna to a handheld unit with 2.5dB antenna. The radio manufactures don't tell you what the receiver sensitivity is but you can estimate that as the Noise Power in 20 KHz of bandwidth is -130dBm (accounts for the noise floor at -174dBm plus the bandwidth noise) and it's reasonable to expect a receiver Cascade Noise Figure 5dB and a signal to noise figure of 7dB, estimating the receiver sensitivity at -118dBm. That would be the point where nothing is intelligible. So add 10dB under perfect clear line of site plus another 10dB in moderate obstruction and you end up at -98dBm. Truthfully, most people use -95dBm as the standard minimum signal strength for sustainable communication and -85dBm preferred. So I'll stick with -95dBm for the examples, but wanted to show how I came up with that number.
So first example, fixed mobile unit with a 6dB antenna to a handheld unit with 2.5dB antenna:

Now, due to Earth curvature, you're never going to realize 90mi unless one of the units is on a hillside, so here is a more realistic example...

Compare that to a handheld to a handheld...

That's all theoretical. Your mileage may vary. I provided the link above if you want to play with numbers...

I'm a nerd, but most of this went over my head. Can you dumb it down and ELI5? Lol

 

[Alaska Steve]

I'm a nerd, but most of this went over my head. Can you dumb it down and ELI5? Lol

The point is that you can estimate the likely range in miles of signal travel using formulas. Besides the hardware characteristics, the actual range is highly impacted by a number of factors: modulation type, foliage density, physical obstructions (hills, buildings, etc.), multipath (things the signal bounces off of which creates ghost signal images); you can account for some of that with 'fade margin', which distinguishes how much signal will be lost due to those factors before the communication is interrupted (works for permeable obstructions but not nonpermeable obstructions). A 50W radio outputs 46.99dBm. A 5W radio outputs 36.99dBm. The difference in radiated power off the antenna, accounting for cable/connector loss and antenna gain, and the minimum anticipated signal strength at the receiver is the 'Free Space Loss', which also accounts for higher 22dB typical nearfield radiation loss off the antenna. I made a mistake in the earlier examples and applied too much fade margin, corrected below. Again, this is theoretical, your mileage may vary....
Mobile 50W, 6dB antenna... to handheld

Mobile 50W, 3dB antenna... to handheld

Handheld to handheld

Again, to be fair, I would never expect these ranges unless you are communicating across open water like a lake or a bay or talking to a repeater on a hilltop. On the ground, you'll probably be lucky to get 10 to 15mi because you're unlikely to find a clear line of sight between the radios over longer distances. The radio system is quite capable as you can see; it's the terrain that governs the link. If you were in an airplane talking to other aircraft or ground control, a 50W radio would suffice; but you're not in an airplane...

 

[pablo94sc]

Gotcha. This is fascinating info, and I think I'm starting to get the hang of it. Thank you.

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