FRS, GMRS, MURS, HAM, CB

So there is some discussion about FMRS vs. HAM vs. GMRS vs. CB. Each one has its advantages and disadvantages. CB is high frequency (HF), FRS and GMRS are Ultra High Frequency (UHF), while MURS is Very High Frequency (VHF). HAM can be all three. Let’s take a look:

No License Required

CB Radio: Citizen’s Band, 11 meter band (~27 mHz)

CB doesn’t require a license, nor is it very regulated. CB’s biggest advantage is also its biggest disadvantage: So many people have them that it’s easy to use them to contact people not in your group, but its also a disadvantage because so many people are both listening and talking over you. Just tune to channel 6 some time and listen to the yahoos talking over everyone with their illegal high powered sets. There are people there that are transmitting with thousands of watts of power. Another big disadvantage is that there are only 40 channels. Sure, you can try tricks like SSB, but if you are going to do all of that, there are better formats than CB. Police are known to routinely monitor CB radio, especially near major highways. I’m not much of a fan of CB. That may be a plus or a minus, depending on whether or not you want to talk to them. Radios run anywhere from $50 on up.

FRS: The Family Radio Service, 462-467 mHz

FRS is a channelized FM radio service that allows families to talk to each other. There are 22 channels dedicated to this service, with channels 8-14 (467 mHz) restricted to 500 milliwatts, and the rest (462 mHz) permitted up to 2 watts. All 22 channels are shared with the GMRS. No license is needed, but like CB, you are limited to certain channels, so traffic may become an issue. They can use tone coded squelch to cut down on congestion, but remember that people not using it can still hear everything you say. The radios must use permanently attached antennas, and this is done because the antennas themselves are designed to limit the range of the radios. Expect the range on these to be somewhere around three quarters of a mile in realistic conditions. Repeaters, phone patches, and the like are prohibited by law on FRS. Radios cost anywhere from $20 on up.

MURS: Multi Use Radio Service

MURS is a UHF service that uses 5 channels in the 151 and 154 mHz band. Up to 2 watts is permitted. No license is required, and there is very little traffic on these channels, but there are a wide variety of radio products that use MURS frequencies. MURS devices include wireless base station intercoms, handheld two-way radios, wireless dog training collars, wireless public address units, customer service callboxes, and wireless remote switches. That may or may not mean interference.


License Required

GMRS: General Mobile Radio Service

This service uses the same channels as FRS, plus an additional 8 channels, for a total of 30. Using these does require a license, but the only real requirement to get one is to be 18 years old, register, and pay a fee of $35. The license is good for 10 years. One license is good for your entire family. Anyone not in the family must get their own license. Transmissions must periodically include the station’s license callsign. If you are using a repeater, the repeater can be used to do that automatically. With the GMRS, you get the 8 extra channels, the ability to use repeaters, and better antennas. This means handheld units get a range of about 2 miles, vehicles about 5, and using a repeater with an antenna on top of your house can get you 20 miles or more of range. Those 8 extra channels are allowed up to 50 watts. Radios are about the same cost as FRS, $20 on up.

HAM radio: VHF, UHF, and HF

HAM radio does require a license, but it allows you a great deal of flexibility. The license isn’t too difficult. The easiest one to get is the technician license, and that requires a small fee and a relatively easy test on basic electronics. With that license, you are good to go on HF, VHF, and UHF. Since there are no channels, you literally have thousands of possible choices. This means that the frequencies will be largely unused and not congested.


Here is what I have done: The only choice from the above list that I don’t have is MURS, but I can program the Baofeng to transmit there, if I have to. In my shack, I have radios that cover GMRS, FRS, and CB, as well as HAM. I like to be as flexible as possible. There is a small antenna farm in my attic.

Each of the above has its own advantages and disadvantages. The disadvantage to a channelized system is that users will be compressed into a limited number of channels. They all have one major disadvantage: they are unencrypted. That means working out code phrases that aren’t obviously code phrases: “John has a long mustache. The chair is against the wall.” Asking someone how Frank is doing could mean something that is known only to the two of you.

The advantage to a non-licensed system is that your friends and neighbors can communicate with you without the need for them to have a license.

Different frequencies and power levels allow you to play physics to your advantage. VHF is easily refracted by vegetation but doesn’t penetrate buildings or rocks very well. UHF penetrates buildings better. A VHF transmission in the woods at low power is unlikely to be intercepted. UHF at low power is great for a block or two in the city, and beyond that is unlikely to be intercepted as well.

If I were to have just one, HAM is the way to go. After that, my second choice would be GMRS.

Communications Training and Gear

With things appearing to deteriorate on a constant basis, I think that it is a good idea for this blog to be a bit more proactive in not just commentary, but in tidbits that people can use. After all, that is why I store and distribute training manuals with the link that the top of the site. With that in mind, I want to put more information out there.

Let’s do communications for this post. It is difficult to fight and resist oppression if you cannot communicate. You also don’t want the secret police rolling you up too easily. When the DOJ was conspiring to overthrow Trump, they were well aware of the NSA’s capabilities, yet they chose to communicate with each other through HAM radios to coordinate this effort, even though such use was in violation of Federal law.

The National Security Agency (NSA) picks up and records almost all electronic communications, thereby effectively wiretapping telephone conversations, email, and practically everything else we send out electronically. What the NSA doesn’t get, their partners in social media and at Google do.

The wife of a Deputy Director of the DOJ was coordinating this attempted coup, and would be well aware of the NSA’s capabilities. There are many technical reasons why spying on HAM radio would be a nearly impossible task. Just by using the frequencies and methods permitted to a person with a Technician license, there are thousands of available channels. Toss in the various modes like Digital, SSB, USB, AM, FM, CW, etc., and then consider that the higher frequencies are short range and would require hundreds of listening stations in every state, and it becomes a very difficult proposition to monitor HAM radio.

A HAM radio running low power on VHF or UHF would be audible for less than a mile or two, making interception a difficult process, at best. A high quality handheld radio that is capable of both the VHF and UHF bands can be bought for about $20. I bought a few of these to loan out to people in an emergency. You can get a nicer one for $70, and that is the one I use. I still own a nicer, far more expensive Yaesu that cost me almost $400, but I have found that the Baofeng works just as well at a fraction of the cost.

I am currently reading “The Guerrilla’s Guide To The Baofeng Radio” and I think it is a great book, full of both technical and practical tips to using this radio. It’s well worth the $23 it cost me. There are other ways to communicate, and we will talk about them later.

Now, the disclaimer: I don’t advertise, and receive nothing for my reviews or articles. I have no relationship with any products, companies, or vendors that I review here, other than being a customer. If I ever *DO* have a financial interest, I will disclose it. Otherwise, I pay what you would pay. No discounts or other incentives here. I only post these things because I think that my readers would be interested.

Be Positive

Miguel points out that many people don’t know their blood type. He says you should find out. It will help you avoid what happened to my friend when he got shot. He needed blood, but we didn’t know his blood type. He kept telling us to be positive, but it’s really hard to do while your friend is dying.

Get yourself a blood tag like one of these, and affix it to your kit, or to your usual range attire. It will save some time when time is critical. (And no, my blood type isn’t B+)

More on Defensive Shooting

Last month, I posted about a shooting at Applebee’s that later appeared to be a defensive shooting by a CCW holder. The police have released more details:

At some point, Hudson got into an argument with a male and female out in the parking lot, and as the pair left in a car, Hudson pulled out a handgun and fired three times into the air. Hudson then walked to a side door that the employees use, which is where a female friend of his tried to get him to leave before police showed up. The release shows that Hudson refused to leave, instead heading into the restaurant and demanding to know who called the police.

Investigators said that Hudson reached into his pants, prompting a patron — identified as 27-year-old Drew Manno — to fatally shoot Hudson. Police added that Manno had a concealed weapon permit and told police he was in fear for the lives of himself and those with him. Hudson’s handgun was not found at the scene, and its whereabouts are unknown at this time. Police said they were able to find the three shell casings from Hudson’s handgun in the parking lot.

Sounds like a good shoot.

The Physics of Manslaughter

Today’s post comes from the UK, and I try not to talk about legal issues in other countries because I just don’t understand the laws in other nations, and don’t want to stick my nose in them. The difference here is that the case involves some technical issues of SCUBA diving and of dive medicine, areas where I feel like I have some level of mastery. This is a technical post, so for those of you who are not interested in physiology and physics of SCUBA, this may or may not be interesting.

A diving instructor in the UK was teaching an experienced recreational diver a course on deep diving. The dive that they did was to 115 feet.

On this dive, they were diving at around 4.5 atmospheres, and this requires some level of care. I don’t see in this account where the instructor messed up, with the exception that I wouldn’t have had a student doing a check dive like this with an 80 cuFt cylinder (which is what the Europeans call 12 liter).

In this case, however, the government brought in a diver from the UK Navy as their expert witness. He testified that the instructor was wrong in three ways- the dive violated the rule of thirds, they were down longer than the dive tables dictated for that depth, and he held his struggling student underwater when the student was attempting to get to the surface, causing his death by drowning.

Let’s start by addressing each of these in turn. The rule of thirds. The rule of thirds is a rule that says you use one third of your air supply to get into the dive, one third coming out, and hold one third in reserve. This rule is generally only used when you are “diving in the overhead,” meaning that there is either a physical or physiological barrier that would prevent you from surfacing. A physical barrier would be diving in a cave, a shipwreck, or diving so deep for so long that you cannot surface because you have a decompression obligation to work through before you can surface. Neither of those was the case here. In that case, the rule is to ensure that you surface with at least 500 psi of gas left in your tank.

The second argument, that the dive tables’ “no decompression” limits for that depth had been exceeded is ridiculous. When you are a new open water diver, you are taught to use tables, but no one, and I mean no one, follows them. The invention of dive computers has rendered them obsolete. The reason for this is that the dive tables assume that you descend at the maximum safe rate from the surface to the maximum depth, then ascend at the maximum safe rate to the safety stop. This is called a “square profile” and no one dives like this in real life. A dive computer monitors your depth every 30 seconds or so, and gives you “credit” for time spent at shallower depths. This has the effect of more than doubling your permissible dive time. Everyone today “dives their computer.”

A great example of this is the standard dive on Florida’s coral reefs. Off the coast of West Palm Beach, there are several reef lines. The most interesting one from a SCUBA perspective is about a mile or so offshore, in 60-100 feet of water. If you were to dive the top of that reef, the tables say that you can spend a maximum of 40 minutes at 70 feet of depth before exceeding the no decompression limit. Most divers will spend a minute or two at that 70 feet, maybe 5 or 10 minutes at 65 feet, then more time at 55 or 60 feet, etc. The result is that divers with computers might well spend 55 to 65 minutes and still not exceed decompression limits. The Commander would have known this, himself being a certified PADI divemaster.

Instead, he contends that the “out of air” situation was so dire that the diver should have been permitted to make an unrestricted surfacing, despite the fact that the student was breathing on the instructor’s plentiful air source. Ridiculous.

I actually did this exact dive here in the states when I got my own extended diving certification some years ago. It is standard practice at the end of any dive that is deeper than 40 feet to stop at a depth between 15 and 20 feet for three minutes. This is called a “safety stop” and is intended to give any gases that have been absorbed in the blood time to diffuse out of the blood and prevent hyperbaric injuries. It’s recommended by each of the three big certification agencies. (NAUI, PADI, and SSI)

Another protocol that some divers follow is to stop for one minute at half of your current depth. So if you had been at 120 feet, a one minute stop at 60 feet is followed by a one minute stop at 30 feet, followed by a one minute stop at 15 feet. No matter how you do it, coming up as slowly as you can is how you avoid hyperbaric injury.

In fact, three of the dive accidents that resulted in injury, and the only diving fatality I have ever been present for was related to a diver ascending too quickly. The physics and physiology of breathing pressurized gases is technically demanding, especially so when diving to depths below 99 feet. Safety stops are VERY important, especially when you are diving at pressures higher than 4 atmospheres of pressure (99 feet).

I myself have had four diving emergencies that required either emergency surfacing or my buddy’s intervention. Three of them were due to equipment failure, and one because I was a moron. One of them required sharing air. We still had time to do our safety stop.

Even so, it’s obvious that the prosecution wanted to railroad this guy. The student in question had a history of high blood pressure, and the autopsy showed that he had alcohol and cocaine in his system. None of this was known to the instructor at the time of the dive.

In this case, the signs of immersive pulmonary edema were there. For those of you who may dive, or who may work in the medical field, pay attention. Immersive pulmonary edema is very similar to the flash pulmonary edema seen with heart failure patients who are suddenly taken off of CPAP. It’s complicated by the changes in pressure caused by depth changes messing with the Renin-Angiotensin-Aldosterone System (RAAS), which regulates blood pressure. Also adding to the complications is the creation of nitric oxide that occurs with sudden pressure changes in SCUBA diving. In patients with hypertension, heart problems, or kidney problems, this combination can be life threatening.

The signs were there: The student was easily winded with mild exertion, he couldn’t perform underwater navigation while at depth (indicating possible mental status changes from hypoxia), and was complaining that he wasn’t getting any air, even though everything was working perfectly ( a sign of shortness of breath). If he was taking an ACE inhibitor for his high blood pressure, this could even make this condition worse.

So how do you treat this? While diving, adopt the rules that I have always followed:

  • Any diver on any given dive can terminate the dive for any reason. This is done by giving any diver in your group a “thumbs up” sign, and is called “thumbing a dive.”
  • Any diver having apparent confusion, disorientation, or an equipment problem should cause the thumbing of the dive.
  • Any diver having shortness of breath should be placed on oxygen as soon as they are on the surface.
  • On the way down, take a few seconds at 65 feet or so to get organized. Look each other in the eye and make sure everyone gives you the “OK” sign.
  • At any dive below 60 feet, make sure that you do your safety stops.
  • Follow other safe practices like ascent rate, NDL limits, and make sure that everyone is diving within the limits of their training and experience.

My Qualifications

My Internet handle has been Divemedic for more than two decades for good reason. I am a certified Master diver, deep diver, mixed gas diver, public safety diver, and Rescue diver. I am certified by all three of the big US recreational SCUBA training agencies at one level or another: NAUI, PADI, and SSI. I have been SCUBA diving for about 30 years. I used to be on a professional dive rescue team. I have been employed at various times as a rescue and salvage diver and had more than 2,000 dives in my logbook, representing more than 900 hours underwater before I stopped bothering to log them, 16 years ago. Enough dives that I have literally worn out a few sets of equipment. I have been present for half a dozen dive casualties, one a fatality. So I understand many of the issues. With that being said, let’s get into the post.