MURS (Multi-Use Radio Service) is a license-free VHF radio service that's been available since 2000. It's governed by 47 CFR Part 95, Subpart J, and it gets almost no attention compared to GMRS or FRS. That obscurity is partly deserved and partly not: MURS has real limitations, but it also has a few things that GMRS can't match.
I own radios on both services. Here's how they compare.
| GMRS (Part 95E) | MURS (Part 95J) | |
|---|---|---|
| License | Required — $35/10 years | None |
| Band | UHF (462/467 MHz) | VHF (151/154 MHz) |
| Channels | 22 simplex + 8 repeater pairs | 5 |
| Max power (handheld) | 5W | 2W |
| Max power (mobile/base) | 50W | 2W |
| Repeaters | Yes | No |
| External antennas | Yes | Yes (60 ft max height) |
| Digital/data modes | Yes | Yes |
| Station ID required | Yes (call sign) | No |
On paper, GMRS wins on almost every metric. More channels, more power, repeater access, and a massive equipment market. MURS's advantages are narrower but real: zero licensing overhead and VHF propagation.
GMRS operates on UHF at 462 MHz. MURS operates on VHF at 151–154 MHz.
UHF penetrates buildings and vehicles better, which makes it the stronger choice in urban and suburban environments. But VHF propagates better through vegetation, forests, and rolling terrain. At the same power level, a 151 MHz signal loses roughly 10 dB less to free-space path loss over a given distance compared to 462 MHz. In practical terms, a 2-watt MURS signal in open, wooded terrain can travel further than you'd expect from the power rating alone.
This doesn't overcome the raw power disadvantage in most situations. A GMRS handheld into a 50-watt hilltop repeater will cover a far larger area than any MURS radio can. But in flat, wooded, or rural terrain where there's no repeater to lean on, the physics of VHF can partially close the gap.
GMRS licensing is already easy — no exam, $35 online, covers your immediate family. But you still need to create an FCC account, file an application, wait for a call sign, and remember to renew in 10 years.
MURS requires none of this. It's licensed by rule, meaning the FCC authorizes anyone to use it without registering. This makes MURS, like FRS, genuinely useful for situations where you need to hand radios to people who aren't your immediate family and don't have GMRS licenses — volunteers at a community event, employees at a job site, neighbors in an informal emergency plan. On GMRS, each of those people would technically need their own license (unless they're in your immediate family). On MURS, the question doesn't arise.
MURS has five frequencies. That's it.
| Channel | Frequency | Bandwidth |
|---|---|---|
| 1 | 151.820 MHz | 11.25 kHz |
| 2 | 151.880 MHz | 11.25 kHz |
| 3 | 151.940 MHz | 11.25 kHz |
| 4 | 154.570 MHz | 20 kHz |
| 5 | 154.600 MHz | 20 kHz |
Channels 1–3 are narrowband only. Channels 4 and 5 allow wideband FM. Before MURS existed, channels 4 and 5 were known as the "Blue Dot" and "Green Dot" frequencies — they were Part 90 business channels, and the inexpensive radios that used them were color-coded with dots on the front panel. When the FCC created MURS in 2000, it reclassified these five VHF frequencies from licensed business use to license-by-rule personal use.
Five channels is workable for a small group, but there's no room for separation if the band gets busy. CTCSS tones help manage this, but they don't prevent interference — they just keep your squelch from opening on other people's traffic.
Though the MURS airwaves are usually pretty dead, you will encounter exceptions. Many businesses such as department stores use MURS radios, and in some cases, their channel plan spans all five available frequencies. Sharing the airwaves may be an issue if you're unlucky enough to be too close to one of these heavy commercial MURS users.
GMRS handhelds can transmit at 5 watts. GMRS mobile and base stations can go to 50 watts. MURS is limited to 2 watts regardless of form factor.
External antennas are permitted on MURS with a height limit of 60 feet above ground (or 20 feet above the structure it's mounted on). A good external antenna at height can extend MURS range significantly, but you're still starting from 2 watts.
GMRS has eight dedicated repeater channel pairs with a 5 MHz offset. MURS has no provision for repeaters at all. Your range is whatever your radio can reach directly.
This is MURS's single biggest practical limitation. A GMRS handheld at 5 watts can hit a hilltop repeater and effectively cover a 20-plus-mile radius. A MURS radio at 2 watts is limited to line-of-sight simplex — in flat terrain, maybe a few miles; in hilly or urban terrain, maybe a few blocks.
This one hurts the most in practice. The GMRS market is enormous and competitive. Dozens of GMRS certified handhelds at every price point, plus mobile radios and repeaters. The MURS market is a fraction of this size. A handful of manufacturers make MURS certified radios, and most are aimed at commercial or industrial use rather than consumers.
The Radioddity MU-5 MURS Radio (Amazon (paid link)) is one of the few consumer-oriented MURS handhelds available. It's a variant of the Radioddity GM-30 GMRS Radio (Amazon (paid link)) — same hardware, firmware restricted to the five MURS frequencies at 2 watts. Beyond that, Wouxun makes the KG-805M handheld and KG-1000M mobile. BTECH has the MURS-V1. Motorola makes the RMM2050. Dakota Alert makes sensor and intercom systems. That's roughly the whole consumer market.
Despite the limitations, there are situations where MURS is the better tool.
Small businesses and farms. Retail stores, warehouses, farms, and ranches use MURS heavily. No license means no paperwork, no per-employee fees, and no compliance questions when staff turn over. Large retailers including Walmart have used MURS frequencies for in-store communication.
Sensors and telemetry. MURS explicitly permits data transmission. The market for MURS-based driveway sensors, motion alerts, and wireless callboxes is well-established. If you need a long-range wireless sensor that doesn't depend on Wi-Fi or cellular, MURS is a legitimate option.
Groups of unrelated people. Events, volunteer coordination, or neighborhood communication where handing out radios to non-family members would create a GMRS licensing gap.
Wooded and rural terrain. If you're primarily operating in heavily forested or rolling rural terrain with no GMRS repeater coverage nearby, the VHF propagation advantage at 151 MHz can partially offset the power disadvantage.
For most people, GMRS is the more capable service. More power, more channels, repeater access, and a mature equipment ecosystem make it the better default for family communication, hobby use, and emergency preparedness. The $35 license for 10 years is a trivial barrier.
MURS fills a different niche. It's the right tool when licensing is impractical, when you need to hand radios to people outside your family, when you're deep in the woods, or when you need license-free data telemetry.
]]>CTCSS (Continuous Tone-Coded Squelch System) is a subaudible pilot tone your radio transmits underneath your voice. Repeaters use it as a gate: if a repeater expects a specific tone and you're not sending it, it ignores your transmission entirely.
Many open GMRS repeaters use 141.3 Hz as their access tone. It's become the de facto "travel tone" for GMRS.
My config sets every channel to transmit 141.3 Hz. Three reasons:
First, it doesn't interfere with simplex. Radios that aren't filtering for a specific tone hear you normally regardless of whether you're sending one.
Second, it gets you into repeaters without reprogramming. When you're traveling and want to try a local open repeater, 141.3 is the most common access tone you'll run into. With it already set, you just switch to the repeater channel and key up.
Third, it can help in marginal conditions. A CTCSS tone is a continuous, stable signal riding below your voice. When your signal is weak, that pilot tone gives the receiver one more thing to lock onto. In my experience, transmitting with a CTCSS tone can help hold the audio squelch open more solidly, regardless of the receiving radio not having tone squelch enabled.
One important distinction: I set this as TX tone only (labeled Tone in CHIRP), not tone squelch (TSQL), which only unsquelches the audio when it receives that tone. I'm sending 141.3 on every transmission, but I'm not filtering my receive side. I want to hear everyone on the channel, regardless of what tone they're using.
This config uses the modern combined 1–22 channel numbering that every current GMRS radio ships with. Before the FCC consolidated the rules in 2017, FRS and GMRS had completely separate channel numbering: FRS had channels 1–14, GMRS had its own channels 1–8 (with repeater inputs), and the overlap was confusing. If you run into documentation or an older radio using a different scheme, the RadioReference combined channel chart has a good crosswalk.
Here's how the GMRS channels break down under the modern numbering.
The shared GMRS/FRS simplex channels. Wideband FM, 5 watts.
| Ch | Frequency | Mode | Power | TX Tone |
|---|---|---|---|---|
| 1 | 462.5625 | FM | 5W (High) | 141.3 |
| 2 | 462.5875 | FM | 5W (High) | 141.3 |
| 3 | 462.6125 | FM | 5W (High) | 141.3 |
| 4 | 462.6375 | FM | 5W (High) | 141.3 |
| 5 | 462.6625 | FM | 5W (High) | 141.3 |
| 6 | 462.6875 | FM | 5W (High) | 141.3 |
| 7 | 462.7125 | FM | 5W (High) | 141.3 |
Per 47 CFR § 95.1767(b), the power limit on these interstitial channels is 5 watts ERP, which is exactly where most HTs top out.
These are the 467 MHz interstitial channels. Two things change here: the mode switches to narrowband FM (NFM), and the power drops significantly.
| Ch | Frequency | Mode | Power | TX Tone |
|---|---|---|---|---|
| 8 | 467.5625 | NFM | 0.5W (Low) | 141.3 |
| 9 | 467.5875 | NFM | 0.5W (Low) | 141.3 |
| 10 | 467.6125 | NFM | 0.5W (Low) | 141.3 |
| 11 | 467.6375 | NFM | 0.5W (Low) | 141.3 |
| 12 | 467.6625 | NFM | 0.5W (Low) | 141.3 |
| 13 | 467.6875 | NFM | 0.5W (Low) | 141.3 |
| 14 | 467.7125 | NFM | 0.5W (Low) | 141.3 |
The eight 462 MHz main channels. This is where the power headroom opens up.
| Ch | Frequency | Mode | Power | TX Tone |
|---|---|---|---|---|
| 15 | 462.5500 | FM | 5W (High) | 141.3 |
| 16 | 462.5750 | FM | 5W (High) | 141.3 |
| 17 | 462.6000 | FM | 5W (High) | 141.3 |
| 18 | 462.6250 | FM | 5W (High) | 141.3 |
| 19 | 462.6500 | FM | 5W (High) | 141.3 |
| 20 | 462.6750 | FM | 5W (High) | 141.3 |
| 21 | 462.7000 | FM | 5W (High) | 141.3 |
| 22 | 462.7250 | FM | 5W (High) | 141.3 |
The 5W here is a handheld limitation. Per 47 CFR § 95.1767(a), mobile, repeater, and base stations can run up to 50 watts on these main channels.
I program the repeater pairs for channels 15–22 as separate memory slots, named after the simplex channel they correspond to: RPTR15, RPTR16, etc. Some factory configs call these "RPTR1–RPTR8" or "RPTR23–RPTR30", which obscures the relationship to the underlying GMRS channel.
You receive on the 462 MHz frequency (the repeater's output) and transmit with a +5 MHz offset on the corresponding 467 MHz main frequency (the repeater's input).
| Ch | RX Freq | TX Offset | Mode | Power | TX Tone |
|---|---|---|---|---|---|
| RPTR15 | 462.5500 | +5.0 MHz | FM | 5W (High) | 141.3 |
| RPTR16 | 462.5750 | +5.0 MHz | FM | 5W (High) | 141.3 |
| RPTR17 | 462.6000 | +5.0 MHz | FM | 5W (High) | 141.3 |
| RPTR18 | 462.6250 | +5.0 MHz | FM | 5W (High) | 141.3 |
| RPTR19 | 462.6500 | +5.0 MHz | FM | 5W (High) | 141.3 |
| RPTR20 | 462.6750 | +5.0 MHz | FM | 5W (High) | 141.3 |
| RPTR21 | 462.7000 | +5.0 MHz | FM | 5W (High) | 141.3 |
| RPTR22 | 462.7250 | +5.0 MHz | FM | 5W (High) | 141.3 |
I set the Skip (S) flag on the repeater channels to skip them when scanning. Since the repeater output frequency is the same as the simplex frequency for that channel (e.g., RPTR20 receives on 462.6750, same as GMRS20), scanning both would just hit the same signal twice. The simplex channels already pick up repeater traffic on the output side.
To find repeaters in your area, check RepeaterBook GMRS and myGMRS. Both maintain directories of GMRS repeaters with frequencies, tones, and locations. Not all repeaters will be listed on these sites, but once you get access to one public, community, or club repeater, that's a good venue to inquire on-air with your local GMRS community about unlisted repeaters.
If the repeater you want to use has 141.3 Hz as its access tone — and many open repeaters do — you don't need to program a new channel at all. Your existing RPTR15–RPTR22 channels already have the right offset and tone. Just switch to the one matching the repeater's output frequency. The only reason to add a dedicated channel would be if you want your channel list to double as a directory of specific local repeaters.
For repeaters that use a different CTCSS tone, add them after your main channels. A common naming convention, used on the directories and in on-air conversation, is location followed by the three-digit decimal portion of the output frequency — e.g., "Omaha725" for a repeater outputting on 462.7250. Be sure to set the Skip flag on any additional repeaters you add, since they're redundant with our 1-22 simplex channels for receiving purposes.
If your radio has a large number of memory channels and lets you key in a channel number directly, it's worth spacing your channel assignments to make channel numbers easier to remember and enter. My layout:
(Actually, I have a few more ranges that I use for some receive-only non-GMRS frequencies I monitor, but you get the idea.)
The NOAA channels get the S (Skip) flag — otherwise, scanning will always stop on the unending NOAA transmissions. The gap between 30 and 101 leaves room for local repeaters etc. without renumbering anything.
A note on NOAA: most GMRS radios can receive the VHF weather frequencies, but some cannot. Others have built-in NOAA shortcuts (a dedicated weather button or menu) that make these presets redundant. If your radio doesn't accept the NOAA channels or already has its own weather access, just delete those entries from the CSV before importing.
This only works on radios with enough memory slots and the ability to leave gaps between them. Many GMRS HTs have constraints on the first batch of memory slots — often the first 22 or 30 must contain the standard GMRS channels in a specific order. The TIDRADIO TD-H3 GMRS Radio (Amazon (paid link)), for example, reserves the first 54 slots for GMRS frequencies. Check your radio's documentation (or just try it in CHIRP — you'll find out fast).
This config is available as a CHIRP CSV file in two variants: HT baseline (5W, all channels enabled) and mobile baseline (50W on main channels, 467 MHz interstitial channels set to receive-only per § 95.1763(d), which restricts those channels to hand-held units only). If your radio supports CHIRP, you can import either file in seconds with a USB programming cable (paid link). See the full CHIRP compatibility list for supported radios and which cable you need.
One thing to check after programming: many GMRS radios default to showing the frequency on the display rather than the channel name. If you've gone to the trouble of naming your channels GMRS20 and RPTR15 and Omaha725, you want to actually see those names. Look for a setting called MDF-A and MDF-B, or Channel A Display Type and Channel B Display Type, and set both to "Name." The exact label varies by radio, but it's usually in the radio's radio settings or channel settings menu, or under the Settings tab in CHIRP with a radio image open.
The config is otherwise standard — standard channel plan, standard offsets, standard modes. The only real opinion is 141.3 Hz CTCSS on everything (transmit only; no TSQL). When you find a local repeater that uses a different tone, reprogram that one channel.
]]>| Antenna | Length | Bands | Pack | Price |
|---|---|---|---|---|
| Baofeng Stubby (paid link) | 1.77" | UHF | 4 | ~$7 |
| ABBREE AR-805S (paid link) | 1.96" | VHF/UHF | 2 | ~$7 |
| Airiton Stubby (paid link) | 2.28" | UHF | 4 | ~$7 |
I tested all three by transmitting into the Bellevue 600 repeater from the alleyway north of Beercade 2 in Omaha—roughly 7 miles from the repeater site. Line-of-sight was heavily obstructed by buildings, trees, and terrain.
My test rig was my TIDRADIO TD-H3 GMRS Radio (Amazon (paid link)) running at 5W. Signal quality was assessed via consensus with operators answering radio checks. (If that was you, reach out for credit—I failed to log callsigns!)
I confirmed these results across multiple sessions, using different TD-H3s and multiple antennas from each pack.
Caveat: with handhelds, your body and the radio are part of the antenna system. An antenna that shines on one HT might be mediocre on another. Because measuring these tiny antennas with a VNA (paid link) is tricky and often misleading, real-world field tests are more useful here. These results reflect my specific setup and conditions.
At these prices, buy a couple packs and test them yourself.
The results reversed my expectations. I expected the popular ABBREE AR-805S to win. But in practice, the Airiton and Baofeng clearly outperformed it.
The 1.96" AR-805S claims dual-band VHF/UHF coverage. On GMRS (UHF), it consistently performed worst for both TX and RX.
Aesthetics are subjective, but its glossy black plastic and huge blue branding look cheap and toy-like. Compared to the other two, it's undeniably ugly.
However:
At just 1.77 inches, this is the shortest antenna tested.
RX performance is good. TX signal reports were solidly in the middle. If you're reasonably close to your intended recipient, it's just as good as my top pick, but it was beaten on TX range in this test scenario.
One nitpick: On the TD-H3, its plastic housing extends too far down, gripping the brass washer on the radio's SMA connector. Unscrewing the antenna often unscrews the washer along with it.
At 2.28 inches and finger-thick with a matte black housing, the Airiton delivered the best overall TX/RX performance by a noticeable margin. The extra half-inch over the Baofeng is barely noticeable. Stick one on a Baofeng UV-5G Mini GMRS Radio (Amazon (paid link)) or TIDRADIO TD-H3 GMRS Radio (Amazon (paid link)) for a highly pocketable setup.
Update: I've since hit the same Bellevue 600 repeater with the Airiton from around 72nd & Maple in Omaha—11.25 miles from the repeater site, on the same 5W TD-H3. Not bad for a $2 antenna shorter than your thumb.
Note: The primary Airiton listing (paid link) can sometimes be out of stock—this alternate listing (paid link) carries the same antenna.
For the absolute shortest profile, get the 1.77" Baofeng. But for the best balance of size, performance, and build quality, the 2.28" Airiton is my favorite.
]]>The FCC publishes its entire Universal Licensing System database as downloadable files, updated daily. These are not small—the GMRS dataset alone contains over 2.3 million records, and the amateur dataset has another 5 million. The files are pipe-delimited text packed into ZIP archives. They are not practical to work with by hand. You need a database, an ETL workflow to get the data into the database, and queries to obtain useful information and reports from the database.
uls provides all of those in one. It downloads these files, parses them, and stuffs everything into a local SQLite database. The initial import takes a few minutes:
❯ uls update -r gmrs
Updating gmrs database...
Importing weekly data...
Imported 2302841 records in 25.1s
✓ Applied weekly import.
✓ Applied 5 daily update(s).
After that, every lookup is instantaneous. No network round-trip, no waiting on the FCC's servers, no browser. Just a callsign and an answer:
❯ uls WRNX451
Call Sign: WRNX451
Name: James R Whitfield
Status: A (Active)
Service: ZA
Address: 742 Evergreen Ter
Location: SPRINGFIELD, IL 627040000
FRN: 0012345678
Granted: 2021-03-15
Expires: 2031-03-15
You can also pass multiple callsigns at once. This is especially handy when you're not quite sure what you heard—was that an N or an M?—just throw both variants at it:
❯ uls WRNX451 WRMX451
No license found for: WRMX451
CALL NAME STATUS CLASS LOCATION
---------- ------------------------------ ------ ----- --------------------
WRNX451 James R Whitfield A - SPRINGFIELD, IL
1 result(s)
The FCC publishes a complete weekly snapshot every Sunday and incremental daily updates Monday through Saturday. uls understands this schedule. After the initial import, running uls update only downloads the daily deltas—small files that apply in seconds. If you set up a cron job or just run the update when you think of it, at least once a week, your local database stays within a day of the FCC's live data. If your data goes too far out of date, the tool will just prompt you to do another full weekly checkpoint download.
Single-callsign lookups are the basic case, but you can also ask broader questions.
Who else in Springfield, Illinois has a GMRS license?
❯ uls search -r gmrs -s IL -c Springfield -a -l 10
CALL NAME STATUS CLASS LOCATION
---------- ------------------------------ ------ ----- --------------------
WQHJ982 David M Archer A - Springfield, IL
WQUH965 Karen L Bennett A - Springfield, IL
WQUI266 Thomas R Castillo A - Springfield, IL
WRAL528 Patricia A Donnelly A - Springfield, IL
WRNX851 James R Whitfield A - SPRINGFIELD, IL
WRDN189 Michael J Erikson A - Springfield, IL
WREQ171 Susan K Fitzgerald A - SPRINGFIELD, IL
WRFG440 Robert W Gallagher A - Springfield, IL
WRFG232 Linda M Hernandez A - Springfield, IL
WRFK121 brian p ingram A - springfield, IL
10 result(s)
You can filter by state, city, ZIP code, name, license status, operator class (for amateur), grant date, expiration date, and more. Sort by name, callsign, state, or date. Limit results or let it run. The data is local, so even broad searches return immediately.
uls supports both GMRS and amateur radio databases. The first time you look up a callsign it doesn't recognize, it downloads the relevant dataset automatically:
❯ uls W1AW
No data found for service 'HA'. Downloading...
Importing data (minimal mode for fast startup)...
✓ Imported 5021553 records from 3 files
Call Sign: W1AW
Name: ARRL HQ OPERATORS CLUB
Status: A (Active)
Service: HA
Address: 225 MAIN ST
Location: NEWINGTON, CT 06111
FRN: 0004511143
Granted: 2020-12-08
Expires: 2031-02-26
For amateur lookups, the search gets more interesting because you can filter by operator class—Technician, General, Amateur Extra—which isn't a concept that exists in GMRS licensing.
The default output is a human-readable table, but uls also speaks JSON, CSV, and YAML. If you want to pipe license data into another tool or script, -f json gives you structured output:
❯ uls WRNX451 -f json
{"unique_system_identifier":4095020,"call_sign":"WRNX451",
"licensee_name":"Whitfield, James R","status":"A",
"radio_service":"ZA","grant_date":"2021-03-15",
"expired_date":"2031-03-15","frn":"0012345678",...}
There's also a built-in REST API (uls serve) if you want to run it as a local service for other applications to query against. In fact, that's exactly what powers the license lookup page on this site—it's just a web frontend talking to uls serve on the backend. Lookups return in under 90 milliseconds.
You can. QRZ, RadioReference, and the FCC's own search all mostly work. But they all require a network connection, they all have their own UI friction, and none of them let you do the kind of bulk filtering that makes a local database powerful. "Show me every active GMRS licensee in my ZIP code" is not a question most web tools are designed to answer quickly.
There's also an offline angle. If you're operating from somewhere without reliable internet—which, if you're using radios, is not an unusual scenario—having the entire FCC database on your laptop means you still have full lookup capability.
It's also much faster than the FCC website. And if you don't want to install anything, you can use the lookup page on this site.
uls is written in Rust and is available on GitHub. Prebuilt binaries are provided for Linux (x86_64 and aarch64), macOS, and Windows. Look under Releases on GitHub. Or cargo install uls-cli if you have a Rust toolchain.
Run uls update -r gmrs to pull down the GMRS database, uls update -r amateur for amateur, or uls update -r all for both. Then run uls --help to see what else you can do.
uls is free and open source, and I tried to break it up into logical reusable components—for example, you could take the code for parsing the public FCC data files and build it into your own application. Pull requests and issues are welcome on GitHub.
I recently added support for several radios across two different hardware platforms. Here's a quick rundown of what that involves.
Before anything else, the naming needs untangling, because the manufacturers and importers have done their best to make this confusing.
The Radioddity GM-30 is a GMRS handheld with its own CHIRP driver (radioddity_gm30.py). The Radioddity GM-30 Plus and Radioddity GM-30 Pro are completely different radios on a completely different hardware platform—they're variants of a platform CHIRP collectively refers to as Baofeng UV-17Pro GPS, living in baofeng_uv17Pro.py. A lot of radios currently on the market are variants of this basic platform: the GM-30 Plus and Pro have more in common with a Baofeng UV-5G Mini than they do with the radio whose name they share.
I own radios on both sides of this divide, and my contributions ended up touching both driver files. The work fell into two separate stories that happened to run in parallel.
The GM-30 already had a working CHIRP driver, written by someone else. I have known for a while that the Baofeng GM-15 Pro is the GM-30 with different trim. That "driver" was four lines of code—a class alias. Same firmware version, different shell, different Amazon listing, different price point.
Then came the Radioddity MU-5, which is the MURS variant of the GM-30. Same hardware again, but the firmware restricts it to five MURS frequencies at 2 watts. The implementation detail that surprised me was how channels 1–20 work.
The MU-5's first 20 channels are fixed to the five MURS frequencies in a repeating pattern. You cannot change them. Not from the front panel, not from the CPS software, not from CHIRP. When you read the EEPROM, the RX and TX frequency fields for those channels contain 0xFFFFFFFF—the same value that means "empty" on every other channel. The firmware doesn't store MURS frequencies in the EEPROM at all. It hardcodes them based on channel number and ignores whatever bytes are sitting in those locations.
This means the CHIRP driver has to do something slightly unusual: for channels 1–20, it returns a frequency that isn't in the EEPROM. It computes the MURS frequency from the channel number, marks the frequency/duplex/offset/power fields as immutable (grayed out in the UI), and writes 0xFFFFFFFF back on save, because that's what the official CPS does. It probably doesn't actually matter what we write back, but this seemed safest.
The GM-30 Plus was the bigger piece of work. CHIRP already had a UV-17Pro GPS driver, and it could talk to the GM-30 Plus without errors, but you could program any frequency, any power level, any mode, and CHIRP would happily write it to the radio. The radio would then refuse to transmit because its firmware knew better.
This is a common failure mode in radio programming software: the tool lets you do something the radio won't. The user sees nothing happen on transmit and assumes their radio is broken.
The FCC restricts the 467 MHz interstitial channels (the ones between the repeater pairs) to low power and narrowband. The GM-30 Plus enforces this in firmware: if the computed TX frequency lands on an interstitial channel, the radio forces low power and NFM regardless of what you've programmed.
CHIRP calls this pattern implied modes—when a radio silently overrides a user-programmed setting based on frequency. The question for the driver is: should it lie to the user (show what's actually in the EEPROM) or tell the truth (show what the radio will actually do)?
The answer, per CHIRP convention, is to tell the truth. When you read a memory from the GM-30 Plus, the driver checks the computed TX frequency. If it's an interstitial channel, the driver returns NFM and low power regardless of what the EEPROM says. When you write a memory that violates these constraints, CHIRP issues a warning—not an error. This distinction matters, because the radio also does something surprising: it allows odd splits and arbitrary frequency assignments from the front panel. It just silently inhibits TX if the result isn't a valid GMRS transmit frequency. The driver mirrors this behavior. It warns you, but it doesn't stop you, because the radio doesn't stop you from programming it that way.
Two more UV-17Pro GPS variants showed up in the mail shortly thereafter: the Radioddity GM-30 Pro and the Baofeng GM-21. Both are GMRS radios with the same frequency-based TX restrictions, but the Pro adds Bluetooth and a per-channel scramble setting that the BF-K6 had but no other UV-17Pro variant exposed.
At this point it became clear that I should refactor the stuff I had added for the GM-30 Plus into a more general "UV-17Pro GMRS-locked variant" abstraction. I extracted the GMRS validation logic into an intermediate class (UV17ProGPSGMRS) and refactored scramble from a K6-specific feature to a _has_scramble flag on the base class. The three GMRS variants became three thin subclasses differing only in capability flags—_has_gps, _has_bt, _has_scramble.
CHIRP is a good example of what its creator calls "successful boring software." It has been around since 2008. It survived a Python 2 to 3 migration and a complete UI rewrite. It has drivers written by people who submitted one PR and disappeared, for radios that are still in active use but no longer manufactured. Changing anything in that codebase is a minefield of implicit assumptions and untestable hardware interactions.
The thing that makes contributing to CHIRP interesting is modeling the behavior of a physical device whose firmware was written by an engineer in Shenzhen who may not have documented their design decisions, for a regulatory environment they may not fully understand, inside a framework that has to round-trip data through a binary EEPROM format without breaking 400 other radios. Every design choice is a negotiation between what the radio does, what the FCC says it should do, what the user expects, and what CHIRP can reasonably represent.
If your radio isn't in CHIRP and you want to fix that, the developer documentation is a solid starting point. If it's a variant of something that already exists, you might be surprised how little code it takes. And if you're lucky, you'll learn something about your radio that even the manufacturer didn't bother to tell you.
For a list of which radios support CHIRP and what cables you need, see the CHIRP compatibility list.
]]>The single biggest friction point for Amateur Radio is the licensing exam. To transmit on ham frequencies, every single operator must study for and pass a technical exam.
GMRS removes this hurdle entirely.
The most powerful feature of GMRS is regulatory, not technical. An Amateur Radio license covers only the individual who holds it. If you want to use radios on a camping trip with your spouse and kids using ham frequencies, every single one of them needs to pass the test and get their own license.
GMRS is designed for families. One GMRS license covers you and your immediate family (spouse, children, parents, siblings, etc.). You can buy a pack of high-quality GMRS radios, hand them to your family members, and immediately have a legal, high-power communication network for convoys, hiking, or neighborhood safety.
For those interested in the technical side of radio, GMRS falls between FRS (the low-power bubble-pack radios) and the complexity of ham radio:
If your goal is to talk to radio hobbyists around the world, get your ham license. But if your goal is to coordinate a road trip, keep track of your family while camping, or just dip your toes into the world of radio frequency without (or while) studying for an exam, GMRS is the easier starting point.
If you're ready to get started, any of these make a good first GMRS radio: the TIDRADIO TD-H3 (Amazon (paid link)), the Baofeng UV-5G Mini (Amazon (paid link)), or, if you just want something simple and cheap, the Baofeng GM-15 Pro (Amazon (paid link)).
]]>Strictly speaking, this is a violation of FCC rules. Yet, it is perhaps among the most flagrantly disregarded regulations in the world of consumer electronics. This disconnect between the letter of the law and the reality of the airwaves raises a complicated question: Does the "Type Approval" sticker on the back of a radio actually matter?
To operate legally on GMRS frequencies in the United States, a radio must be "Type Accepted" under Part 95E of the FCC rules. This means the manufacturer has submitted the radio to the FCC, which has verified that it adheres to specific technical constraints—power limits, bandwidth restrictions, etc.
When a ham radio operator uses a standard amateur radio (approved under Part 97) to transmit on GMRS, they are technically breaking the law. Part 97 radios are designed to be frequency-agile and user-programmable, features that the FCC generally restricts in Part 95 services to prevent interference.
However, many enthusiasts point out that this distinction is often hardware-agnostic. There are numerous examples in the market where a "GMRS Approved" radio and a "ham" radio share identical internal circuitry. The only difference lies in the firmware: the GMRS version is software-locked to specific frequencies and power settings to satisfy the FCC, while the ham version remains unlocked. Many of these swaps are hilariously quick and dirty: in my work contributing to CHIRP, I've encountered radios whose MURS version still internally identifies as the GMRS model, for instance, because they literally changed nothing except the whitelisted frequencies and the FCC ID. In these cases, the difference between legal and illegal is a matter of configuration and an administrative stamp of approval.
Some manufacturers even blatantly document an unlock procedure for their GMRS radios, effectively selling a ham radio in a GMRS-labeled box. So far, they've been getting away with it, too. I guess if the radio is locked when it's in front of the FCC, and the user unlocks it later, that's on the user, not the manufacturer? It's difficult to interpret the machinations of the FCC, but it's clear that they're not doing a great job of enforcing their own rules. And when they do, they tend to do it in a lurching, inconsistent manner, like that time they decided to start enforcing the rules against Baofeng importers through a public notice that no one read but everyone seemed to interpret to mean "Baofengs are illegal now". But that's a story for another time.
If the hardware is often identical, why does the rule exist? The danger of using non-approved radios usually isn't the radio itself; it's the person programming it.
GMRS has specific requirements regarding frequency deviation (how "wide" the signal is) and power output. A dedicated GMRS radio is hard-coded to adhere to these rules. A generic ham radio, however, puts those variables in the hands of the user. An underinformed consumer might unwittingly program a radio to transmit "Wide" (25 kHz) on a channel restricted to "Narrow" (12.5 kHz), causing their signal to bleed into adjacent channels and disrupt other users. They might blast 50 watts of power on a channel restricted to 5 watts.
The Type Approval process is, in part, the FCC's way of "idiot-proofing" the airwaves. By ensuring the radio cannot physically do the wrong thing, they protect the spectrum (mostly) from well-meaning but ignorant users.
Despite the strict regulations, the practical reality of enforcement tells a different story. The FCC's enforcement bureau generally focuses its limited resources on significant sources of interference or commercial entities blatantly flouting the rules.
History shows that while the FCC aggressively pursues manufacturers and importers who market non-compliant radios as GMRS-ready (forcing them to lock frequencies or change labeling), there is virtually no track record of individual users being fined solely for using a clean-sounding Baofeng on a GMRS repeater. If a user's signal is clean, within bandwidth limits, and not causing interference, the "crime" is invisible. The regulatory body seems less concerned with the sticker on the device and more concerned with the actual integrity of the airwaves.
This creates a paradoxical environment. On one hand, the law is clear: using a non-approved radio on GMRS is illegal. On the other hand, if a knowledgeable operator configures a high-quality commercial or amateur radio to perfectly mimic the technical standards of GMRS, the only victim is a bureaucratic process.
So, should you use your unlocked ham radio on GMRS frequencies?
The regulations exist to defend against the effects of technical incompetence. If you do not understand deviation, spurious emissions, or Part 95E power limits, using a non-approved radio is a liability to yourself and the community.
If you have to ask, the answer is no.
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