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The reference is for the exhaust tuning of the internal combustion engines. This is not only similar physics behind it (and fallacies) but exactly the same. The same wave theory applied to processes inside exhaust pipes and antenna feeders. The point is to match the impedance and reduce the amplitude of reflected waves to not waste energy on pushing exhaust gases through the pipes, and the current through the feeder line and antenna. Two-stroke engines are especially sensitive to exhaust tuning, because they relay great deal on the wave processes inside the pipes (SWR, if you wish) to ventilate out the wasted gases and fill the combustion chamber with the fresh fuel/air mixture. Four-stroke are less sensitive to exhaust tuning (but still are!) but more sensitive to intake tuning for the very same reasons - wave behavior in the transmission lines (intake and exhaust manifolds and pipes). So, the nature of the phenomena is different, but the physics behind it the same, so are misunderstandings.

The more I learn about the FCC's General Mobile Radio Service (GMRS), the more I am fascinated by RF in general. It touches everyone's lives every second of every day, yet few people pay much attention. How cool is it that after 42 years and 14 billion miles away, the 22-Watt radio on Voyager 1 is still sending data back to earth every day (how important is that antenna?). So why aren't more people interested in GMRS or RF in general? There's no test to get a license like amateur (ham) radio. It's $70 for a 10-year license, and is really easy to get started. So here are some theories. People don't know: GMRS exists Why GMRS exists Why they'd want to use GMRS How to envision themselves participating in GMRS What it takes to get started with GMRS What it takes to continue and improve with GMRS Technical information they should know about GMRS Etiquette when transmitting (TX) on GMRS What a GMRS "Net" is and why Most people within the GMRS community are helpful once you're in, but the community is very inviting in a go-figure-it-out-yourself way, and no one has assembled everything you need to know about GMRS all in one place. We GMRS people are putting the onus on outsiders to sift through thousands of painfully esoteric webpages with a winnowing fork, separating useful info from useless, poorly written, or incomplete info. When I first heard about GMRS on a 4x4 trip, I arrived home and Googled around and settled on a Midland MXT-275 because it seemed perfect for mounting on my truck dashboard. At the time, I had no idea that Midland doesn't manufacture a GMRS radio capable of operating on split-tone repeaters (Dear Midland, I know you're reading this: why do you squander so much potential?). Edit 6/28/2021: Midland heard our cry! They just updated the MXT-275 to include split-tone programming on repeater channels. So for example, now this radio is able to reach a repeater that receives (RX) incoming transmissions on 467.550 with a PL tone of 103.5 and repeats the transmission (TX) at 462.550 with a PL tone of 88.5. I didn't even know what "split tone" was or even what "tone" meant, or carrier or squelch or hundreds of other little things you all take for granted. Since then, I realized that if the big, bad manufacturers like Midland, Kenwood, Motorola, and iCom can't even invite the public to learn more and provide useful content for each stage of the customer journey—Awareness, Consideration, Purchase, and Loyalty—the 2-way radio industry has much deeper problems and aren't there to help guys like me. As we get involved deeper into GMRS, there's little-to-no hand-holding going on at each level of knowledge. I ending up relying on the Ham community here and there and a guy who is basically a saint at a little radio shop in Phoenix, Arizona (hope Tim over at Procomm and the others at the nonprofit AZGMRS.org don't mind me giving them a shout-out). Edit 4/14/2020: By the way, AZGMRS made this awesome list of FCC-approved GMRS radios that they recommend. If you live anywhere near Arizona and are reading this, now would be a great time to become a member. Their repeater network covers some 100 miles around Phoenix with more and more repeaters joining the network (check out their sweet coverage map). But it's still frustrating. I wish a GMRS expert—presumably a manufacturer—would just come out and say exactly what a total newbie needs at each stage of their involvement or level of need. Two-way radio manufacturers should stop wasting time trying to sell, and start marketing and branding, which means educating the public about the 5 W's (Who, What, Where, When, Why [+how, +how much]) without trying to sell to them. Most new users don't know what they need because they don't know what's possible. For example, I wish I knew that manufacturers don't typically include the best antenna on their radios right out of the box. It took me over a year to realize that the best bang for the buck for a portable base antenna to include in my go bag is N9TAX's Slimjim and that Smiley Antenna makes the best bang for the buck antennas for hand-held radios (which by the way, everyone just assumes newbies are supposed to know that hand-held walkie-talkie radios are called "HT" for "Handy-talkie" and what a "QSO" is). How would a newbie know that the cheap Nagoya 771 "upgrade" antenna for Baofengs that everyone talks about actually isn't the best bang for the buck for the GMRS frequency band of 462–467? How would a newbie know that antennas work best when tuned exactly to what they call a "center" frequency that accommodates 5 Megahertz in each direction (+5 and -5 Megahertz) at the expense of hearing other frequencies? I learned the hard way that in order to properly install an NMO antenna mount on the roof of my truck, I would need a drill bit specifically made for drilling NMO antenna mount holes, and that yes, it is worth the money to do it right the first time. I'm still in the middle of learning how a "quarter-wave" or "5/8 wave" antenna works, the difference between dB gain vs. dBi gain, mic gain, antenna gain, because again, everyone seems to just assume I already know what all this means. I still don't understand what antenna "tuning" means and why you have to "cut" an antenna to "tune" it. Can I make my own antenna right now in a pinch with a copper wire in my garage? Ok, show me! How do I measure it or test it? What is SWR? Can I measure it myself? What do I need in order to measure it? Is one SWR meter better than another for my level as a newbie? Is there something I should learn to make it worth buying the better meter that opens up a whole new world of capability? Is it worth learning all that? This graphic did a great job beginning to explain what dBd gain means for those of us who know next to nothing about it, but now I need to go find out on my own and sift through a thousand webpages to find out if dBd is something new I need to know. Speaking of dB, I know that "dB" is a decibel, but is it the same as my stereo volume? Why do I see manufacturers saying that the microphone and cable have a dB rating? What is going on here? This is madness! We can Google things all day, but which info is true and correct and the most helpful? I think that the entire industry is sitting on a Gold Mine of consumers sitting at home for weeks on end who would love to buy GMRS equipment and communicate via GMRS to friends, family, neighbors, and other GMRS users. Whoever provides the most useful, relevant, and engaging content that stops making assumptions about what people know or don't know will win. STOP ASSUMING. START EDUCATING.

Same with me. I enabled all three of my TK-880 for the front panel programming, and I used it, let me remember how many times... oh yeah, never! I do keep a printed reference card in the glovebox, just in case of apocalypse, or when I'm tooooo bored. With the handhelds TK 3170 I did not even bother to enable FPP. Too much trouble.

As axorlov mentioned the Kenwood TK-2170/3170/3173 radios have a table for 40 tone entries so those aren't much of a problem. The radios do offer "Operator Selectable Tone (OST)" you can assign the function to one of the PF keys on the radio. This allows you to select one of the pre-stored tones in the tone table. The Kenwood TK-270G/370G, TK-2140/3140 radios have only 16 entries for the tone table. Those are of course more restricted. The radios I'm looking at to revise the code plugs are the TK-2140 and TK-3140 radios. With only the option to program in 16 tones I wanted to pick ones the are most likely to be used. By the way the TK-270G, TK-2170 and TK-2140 are VHF radios while the TK-370G, TK-3140 and TK-3170/3173 are UHF. And yes these radios could be programmed through the front panel, BUT you need to remove a small surface mount component off a circuit board inside in addition to enabling the function in the programming software. This is all covered in the service manuals for the radios. After looking at the very inconvenient multi button pressing while powering up the radio plus the rather cryptic multi layer menus you have to go through it really isn't worth the trouble.

They do have a right to inspect your station - but the "castle" doctrine of law means that they need your permission to enter your premises. Now a court order - well that's an imperative legal directive no matter what agency applies for it. What ever the court order says you let happen, lest you run afoul of the courts.

Retired LEO here. That is not a likely scenario. Your local PD/SO might take a report, but they're probably not taking any action other than forwarding it to the FCC. Your local law enforcement agency probably lacks the resources and knowledge to address it. The FBI has bigger fish to fry. The FCC is not searching any residences without a warrant. There is a history of long operating pirate radio stations and obnoxious interference from both licensed and non-licensed operators that have taken years to be addressed by the FCC. Google "FCC Enforcement Action" and you will see that the process involved to stop illegal/unlawful transmission is long and cumbersome. Tuning around the amateur bands will reveal the same operators, night after night, interfering, cursing, and being a general nuisance. If the FCC had no-warrant search ability, these high power offenders would be the first to go, since they are heard nationwide, and in some cases, worldwide. Some obnoxious dude on FRS/GMRS is way down the list for enforcement.

They are mutually exclusive. One or the other, not both. Michael WRHS965 KE8PLM

That's the idea! Making unlicensed folks w/o a callsign people think twice before transmitting on a repeater channel is what we want. Keeps the riffraff out.

As a GMRS licensee they (and you) are required to use them. I live near Cincinnati. Around me, both repeater and simplex users alike seem to use them pretty religiously. There is even a local GMRS father that is teaching his 7 year old son to use GRMRs per the rules. Pretty cool seeing a father take his role seriously. Remember that GMRS shares 22 of 30 frequencies with FRS, and FRS users do not need to have a license and callsign, so one cannot always assume that those not giving there callsign are actual GMRS licensees. They could be simplex FRS users. Now, if you are hearing them truly from the repeater (not just simplex users using the main GMRS frequencies and code that you are), then yes they must have a license and must be using there callsign. Best way to get people to use their callsign is to lead by example. Michael WRHS965 KE8PLM