Most people today use smartphones to talk to others without realizing that they are basically using radio transceivers.
Radio transceivers are everywhere and can have many forms and shapes:
Hobbyists use CB radios, parents use baby monitors, on the beach you might use a wireless Bluetooth speaker.
Licensed HAM radio amateurs experiment with long-range radio transmissions, and many professions use their own radio networks—such as police, emergency services, aviation, and businesses.
Even though walky talkys, babyphones, and bluetooth speakers may look much different from smartphones, they all fundamentally do the same: they transmit voice information via radio waves.
In this article, we’ll be looking at the technical and legal requirements to transmit voice wirelessly.
Overview
To better understand how wireless voice transmission works and what your options are, let’s start with the ubiquitous smartphone.
Smartphones – Digital Walkie-Talkies
Smartphones really are highly sophisticated digital walkie-talkies operating across a variety of frequency ranges:
| Technology | Example Bands (MHz) | Typical Use |
|---|---|---|
| 2G | 900, 1800 | GSM (Europe/Asia) |
| 3G | 900, 2100 | UMTS/WCDMA |
| 4G | 700, 800, 1800, 2600 | LTE (global) |
| 5G | 600, 3500, 26000 | Low, mid, mmWave 5G |
Users are shielded from all technical complexity. The smartphone automatically selects the appropriate frequency band based on your carrier, location, and the available network technology.
When you dial a number, the smartphone connects to your network and requests the location of the target number. Once the network determines where the recipient is currently located, it routes your voice data packets to the target device—much like data packets in a computer network.
Essentially, smartphones use radio frequencies only for the “last mile”: your device connects to the nearest radio tower, while the rest of the communication path is typically handled by wired infrastructure.
Analog Walkie-Talkies
In contrast, classic analog walkie-talkies use radio waves exclusively: the entire communication from source to destination is transmitted directly, with no intermediaries. This means there is a natural range limit (maximum communication distance).
Some services use repeaters to extend the range: the radio connects to a repeater station, often located at an elevated position. The repeater then retransmits your signal on another frequency that all walkie-talkies in the area listen to. With repeaters, walkie-talkies send and receive on different frequencies. While repeaters can extend the range, they typically cannot relay signals through multiple repeaters, so the overall range—though improved—is still limited.
This type of communication is still heavily used, for example by aircraft (Airband), classic walkie-talkies, and HAM radio amateurs.
Digital Walkie-Talkies
Digital technology has become very affordable in recent years, leading to an increasing number of digital walkie-talkies.
Digital walkie-talkies basically use the same technology found in smartphones:
- Peer Mode:
When operating stand-alone (without an underlying network), voice information is sent as data packets and can be received by anyone within range who also has a compatible digital walkie-talkie using the same frequency and protocol. -
Simple Networks:
Some license-free bands, like PMR446 Digital (DMR446), allow digital communication with support for channels and talk groups.You can target specific groups, but you cannot “call” a specific person. This is because free networks have no central registration, so it is not possible to uniquely identify individuals.
-
Full Networks:
Licensed HAM radio amateurs, commercial users, and authorities use global networks like D-STAR, DMR, and TETRA, which function similarly to telephone networks.In these networks, users are registered and can be uniquely identified by their ID, allowing you to “call” a specific person. The voice data packets are then routed to that person across the network, regardless of their location.
A crucial advantage of digital transmission is the ability to securely encrypt information, i.e. by using AES256 encryption. Analog radios can, at best, “scramble” voice information, which is far less secure.
Unlike commercial users and businesses, HAM radio amateurs are not allowed to encrypt their communications.
Low-Range Voice Transmission
There are many more devices that also transmit voice wirelessly via radio waves: baby monitors, wireless speakers, wireless headphones, and similar products are all essentially walkie-talkies, though they typically transmit voice in only one direction.
These devices are intended for (very) short ranges—essentially, just connecting one device to another nearby, or monitoring a baby room in close proximity.
That’s why such devices often use WiFi or Bluetooth.
Voice-Only Radio Services
If you are interested in transmitting voice over larger distances - independent from existing infrastructure and smartphone coverage - you need to select a radio frequency range where it is legal for you to transmit.
There are a number of license-free frequency ranges for voice transmission that anyone can use.
Regulations may vary from country to country. The table below lists typical regulations. Always make sure you understand the specific regulations that apply to you in your current location.
Most license-free services use analog technology and no repeaters, so the overall reach is limited to a few kilometers.
| Service/Device | Analog/Digital | Typical Frequency Range | Max Power (Legal) | Legal Requirements/Notes |
|---|---|---|---|---|
| CB (Citizens Band) | Analog (AM/FM/SSB) | 26.965–27.405 MHz | 4 W (AM/FM), 12 W (SSB) | License-free |
| Freenet) | Analog & Digital | 149.0125–149.125 MHz | 0.5 W (handheld only) | License-free, Germany only |
| MURS (Multi Use Radio Service) | Analog (NFM) | 151.820–154.600 MHz | 2 W | License-free (US) |
| LPD433 (Low Power Device) | Analog FM | 433.075–434.775 MHz | 10 mW | License-free in the EU |
| PMR446 (Private Mobile Radio) | Analog FM & Digital (DMR) | 446.0–446.2 MHz | 0.5 W ERP | License-free, EU/Malaysia/Singapore/Norway/UAE |
| FRS (Family Radio Service) | Analog (NBFM) | 462.5625–467.7125 MHz | 2 W (main ch.), 0.5 W (others) | License-free |
Licensed Public Radio Services
Some frequency ranges require a special license:
| Service/Device | Analog/Digital | Typical Frequency Range | Max Power (Legal) | Legal Requirements/Notes |
|---|---|---|---|---|
| Air Band | Analog (AM) | 108–137 MHz | Varies (typically 5–25 W) | Aviation license, strict regulation |
| 2m Ham Band | Analog & Digital | 144–148 MHz (US), 144–146 MHz (EU) | Up to 1.5 kW (US, licensed) | Amateur radio license required |
| 70cm Ham Band | Analog & Digital | 420–450 MHz (US), 430–440 MHz (EU) | Up to 1.5 kW (US, licensed) | Amateur radio license required |
| GMRS (General Mobile Radio Service) | Analog (NBFM) | 462.5625–467.7125 MHz | 5 W (handheld), 50 W (base/mobile) | License required (US) |
- Air Band: Radio station license (for the equipment/aircraft) and Operator License (for the operator/pilot)
- HAM radio amateur: Non-commercial experimental use, large frequency ranges with high RF power, requires deep technical and legal knowledge
- GMRS: Shares the same frequency range with license-free FRS. The GMRS license allows more RF power and the use of repeaters which can extend range:
| Channel Range | Frequency Range (MHz) | FRS Max Power | GMRS Max Power | Shared? |
|---|---|---|---|---|
| 1–7 | 462.5625–462.7125 | 2 W | 5 W | Yes |
| 8–14 | 467.5625–467.7125 | 0.5 W | 0.5 W | Yes |
| 15–22 | 462.5500–462.7250 | 2 W | 50 W | Yes |
| 15R–22R | 467.5500–467.7250 | Prohibited | 50 W | GMRS only (repeaters) |
Multi-Purpose Frequency Bands
Aside from the designated voice-only services, additional license-free multi-purpose frequency ranges exist. They can be used to transmit voice but are used for a range of other data as well.
| Service/Device | Analog/Digital | Typical Frequency Range | Max Power (Legal) | Legal Requirements/Notes |
|---|---|---|---|---|
| WiFi (IEEE 802.11) | Digital | 2.4 GHz, 5 GHz, 6 GHz, 60 GHz | 100–1000 mW (region/band dependent) | License-free |
| Bluetooth | Digital | 2.4 GHz ISM band | 1–100 mW (Class 1: 100 mW, Class 2: 2.5 mW, Class 3: 1 mW) | License-free |
| ISM (Industrial, Scientific, Medical) | Analog & Digital | 315, 433, 868, 915 MHz (region dependent) | 10–100 mW (typical, varies by band) | License-free, strict duty cycle/power limits |
Devices like Baby Monitors, wireless speakers, wireless headphones, etc., all use one of these bands and share it with other devices such as garage door openers, sensors, and other devices that transmit data other than voice.
Most DIY projects use breakout boards with transceivers operating in one of these bands.
While you can use these to design and build your own analog or digital walkie-talkie, there are important restrictions you must know:
- Low Power: These bands are reserved for low-range devices, and the maximum output power is very low. Using higher-than-allowed power can easily interfere with other devices in the vicinity. If your neighbor can no longer open their car with the key fob, you’ll quickly trigger investigations by local authorities like the FCC or Netzagentur, and be subject to severe fines.
- Duty Cycle: Since these bands are primarily used for short data transmissions like garage door opener codes or sensor data, there are duty cycle restrictions for most of these bands: you cannot transmit for longer periods of time. Voice communication typically requires much higher duty cycles than are legal to use.
In a nutshell, for voice transmissions avoid these bands.
A much more cost-effective and simpler way is to use one of the designated voice transmission services listed above, and purchase a dedicated walkie-talkie.
Analog vs. Digital
Digital transmission uses much more modern techniques, resulting in significant advantages (better audio quality, less static, longer battery life, effective encryption, better bandwidth usage, etc.):
| Feature | Analog | Digital |
|---|---|---|
| Cost | low | higher |
| Audio Quality | Lower than digital in cheaper systems. | Clearer audio with less background noise and static |
| Interference | Audible noise and signal degradation. | Muting or dropout rather than noisy audio. |
| Latency | Real-time transmission. | Typically 3–5 ms due to digital processing |
| Channel Efficiency | One conversation per channel | Multiple conversations per channel |
| Security | No effective encryption | Secure encryption possible (though often illegal to use) |
| Battery Life | Shorter, constant transmission power needed. | Up to 40% longer battery life |
| Coverage | More static and noise at coverage edges. | Clearer audio at coverage edges due to error correction. |
| Expandability | Limited | Data can be incorporated into transmission (e.g., caller ID, GPS position, etc.) |
| Privacy | none | strong encryption available (may be illegal to use) |
| Mesh/Network | no | DMR, D-STAR, TETRA, etc. |
Whether or not you are allowed to use digital transmission depends on the radio band you are targeting:
- CB, LPD433, FRS, GMRS, and MURS are all analog only.
- Freenet) and PMR446 allow both analog and digital modes.
- HAM Radio: licensed HAM radio amateurs can use any mode they want. Encryption is not allowed, though.
Using Legal Radios
To legally operate on one of the license-free bands, you must (1) adhere to the technical restrictions and (2) use a certified radio.
Certified Radios
Certified radios from reputable brands guarantee that you operate within legal limits. Such radios work out of the box, with no confusing configurations or settings to learn.
They undergo careful design and extensive testing, and the built-in antenna is typically perfectly tuned to the frequency range you intend to use. You can use these radios out-of-the box with next to no technical background.
On the downside is cost: certified radios cost a multiple of the price of uncertified radios.
Cheap “Illegal” Radios
While generic Chinese radios are much more affordable and can be programmed to use the required frequencies and power levels for license-free bands, they are typically not certified—and thus illegal to use on one of the license-free bands in most countries.
Such radios aren’t illegal per se. They are just illegal to use without a proper license and/or on one of the license-free bands.
As an analogy, while you can ride a bicycle license-free, a driver’s license is required for a Ducati because there is just much more risk involved for you and bystanders if you don’t know what you are doing.
- Certified Radios: Fool-proof to operate, no special knowledge required by the user.
- Uncertified Radios: Highly flexible, require technical understanding and programming. Used inappropriately, such radios can easily cause severe interference. That’s why such radios require a license, i.e. HAM radio amateur.
Even such a license wouldn’t allow you to use these radios on one of the license-free bands. You’d be restricted to the frequency ranges specifically assigned to HAM radio.
Why is it illegal?
There are a number of very good reasons why uncertified radios are illegal to use without a proper license:
-
Spurious Emissions:
Many cheap radios emit so-called spurious emissions: when you transmit, you send not only on your own frequency, but also in parallel on higher harmonic frequencies (typically 2x, 3x, 4x, etc. the frequency you dialed in).Harmonics are a general problem of radio transceivers, yet cheap radios lack the suppression found in more expensive certified radios. Using cheap radios may therefore severely interfere with emergency and other services in other frequency ranges—without you even noticing.
Licensed HAM radio amateurs have the test equipment to detect harmonics, and the knowledge and means to attenuate them if present.
-
Illegal Power:
Even though most cheap Chinese radios do not reach the output power they claim, such radios often still produce more output power than allowed.For example, PMR allows a maximum of 0.5W. Even low-end uncertified radios can transmit with 1–5W.
Sending with more power does not necessarily improve your reach: you’d need to quadruple your power to double your reach. By doing so, your radio starts to emit very high RF signals with a good chance of interfering with other services in your vicinity.
-
Antenna:
Part of many regulations is your effective RF power, which depends on additional factors like the antenna you are using.That’s why certified radios often come with a fixed rubber duck antenna, whereas uncertified radios use an SMA adapter that lets you connect any antenna you like. By using a larger or directional antenna, you can easily exceed the legal effective RF power.
Caveat: Pre-Programmed Channels
To see just how easily unlicensed users can get in trouble with uncertified radios, keep in mind that such radios typically come pre-programmed on frequencies that are assigned to emergency services, military, or other non-public services.
Anyone who simply unpacks such radios and starts using them is actually transmitting on highly illegal frequencies, causing interference and subjecting themselves to severe fines.
That’s because most Chinese radios are not designed for a specific license-free band. Instead, they can work on multiple bands and must initially be programmed correctly.
When High RF Power Backfires
“Man, I got this 10W walkie-talkie from AliExpress, that’s 20x the power of your certified radio, you loser!”
Sentences like this indicate once more why users without technical background should stick to worry-free certified radios. Here is why:
-
False claims:
Regardless of what sellers of no-name radios claim: most radios use the same or similar components and emit 2–5 W RF power, depending on the frequency you use.Very cheap entry-level radios emit 0.5–1W.
-
False assumptions:
To significantly increase reach, you need to increase RF power disproportionately: it takes 4x RF power to double the reach.Higher RF power comes at an expense: battery life shortens drastically, and if your antenna is not excellently tuned, the HF amplifier inside the radio may heat up and eventually get damaged.
-
Low Receiver Sensitivity:
Some no-name radios come with below-average receiver sensitivity. When the receiver is less sensitive, you need more transmit power on the other end.Investing in quality radios with excellent receiver sensitivity is just as effective as increasing RF transmit power—except this is legal and saves battery power, too.
-
Bad Antenna:
The most important caveat with no-name radios is their antennas: more often than not, the included rubber duck antenna is badly tuned, especially with multi-band radios that cover a wide frequency range.They may work great for some frequencies but typically not for the ones you target.
It is not uncommon to see SWR ratios of 1:6 to 1:14: only 1/6 to 1/14 of the original RF power is actually emitted, the rest flows back into the amplifier and heats it up.
Keep in mind that raw RF power is only one factor of many that contribute to reach. Other important factors are receiver sensitivity and a well-tuned antenna.
So a uncertified (illegal) 5W radio with a 1:14 SWR antenna emits just 0.36 W, whereas a certified 0.5W radio with a well-tuned 1:1.1 SWR antenna emits 20% more: 0.45W.
Combined with a better receiver sensitivity, the certified radio may even end up with a much better reach—at 10x less battery consumption, and completely legal.
If, on the contrary, you are brute-forcing reach by pumping up just the RF power, you disproportionally waste battery power, you may cause local interference and strong harmonics, and you make your signal much more noticeable by unwanted eavesdroppers.
Using Uncertified Radios
Let there be no mistake: there are a number of awesome and technically highly sophisticated uncertified Chinese radios, packed with technology at unbeatably low prices. And these radios are perfectly legal to operate with the proper license (i.e. HAM radio).
For example, take the Radtel RT-4D: it supports both analog and digital transmission with dual-band support for 2m and 70cm (essentially covering all VHF and UHF bands) and has an exceptionally sensitive receiver.
It can receive almost the entire frequency range from 18 MHz up to 1 GHz, including 27MHz CB band, and even supports strong AES256 encryption in its digital modes. All this in a very small form factor and with a strong rechargeable battery.
That’s impressive for a price tag of less than €50.
As discussed, such powerful general-purpose radios require a license to operate: operating them is not fool-proof and requires technical know-how.
These are some of the steps a responsible licensed HAM would take before using such a radio:
- Code Plug: Download the configuration software for the particular radio, and create an appropriate code plug (radio configuration): program the channels according to the frequencies and modes that are legal to use, and upload the configuration to the radio.
- Harmonics: Use a tool like Tiny SA to analyze spurious emissions. Make sure the radio is emitting only on the designated frequency, and unwanted emissions on other frequencies are attenuated by at least 60 dBc. Perform adjustments, e.g., by adding band pass filters, to ensure unwanted harmonics are adequately suppressed to avoid causing interference.
Choosing Frequency (Band)
Public license-free bands use three different frequency bands: 11m, 2m, and 70cm (wavelength).
These bands perform fundamentally different:
- HF (11m): CB (Citizens Band) uses the 11m band/27 MHz shortwave.
- Large antennas
- Relatively high power consumption
- Long distance over terrain and across hills
- Pricier equipment
- VHF (2m): Freenet), and MURS use the 2m band/149–155 MHz
- Small antennas
- Good with obstacles (no free line of sight required)
- License-free use only in limited areas of the world
- UHF (70cm): PMR446, FRS, GMRS, and LPD433 use the 70cm band/446–467 MHz
- Very small antennas
- Perfect for indoor communication
- Very affordable
In a nutshell:
- Long Range: 11m is ideal for long-range communication, especially when there are natural obstacles like hills interfering with line of sight. On the downside, 11m requires large antennas, and the equipment is generally more costly.
- Urban/Indoors: 70cm is ideal for urban environments, especially inside houses or structures. Antennas can be very small, and transmission is energy-efficient. 70cm may not work across hills or from valley to valley, though.
- General Purpose: 2m combines aspects from both: it works well in urban environments and over terrain.
| Property | 11m | 2m | 70cm |
|---|---|---|---|
| Antenna Size | 1–2.5 m | 0.5–1 m | 10–20 cm |
| Range (indoors) | Moderate | Good | Very good |
| Range (urban) | 1–3 km | 1–2 km | 0.5–1.5 km |
| Range (line of sight/open) | 5–10 km | 3–5 km (if license-free) | 2–5 km |
| Propagation | Good over terrain | Good in open/urban | Penetrates buildings well |
| Susceptibility to Interference | High (atmospheric, man-made) | Medium | Low (mainly local interference) |
| Channel Congestion | Medium | Low, rare use | Medium to High (urban areas) |
| Power Consumption | High | Medium | Low |
| Building Penetration | Moderate | Good | Very good |
| Equipment Availability | Widely available | Limited | Very widely available |
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(content created Mar 10, 2025 - last updated Jun 04, 2025)