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best fm transmitters

The Best Car FM Transmitters in 2021

Author: Robert Wilson

Electronics & Peripherals Expert

An individual music experience is difficult to live out in an older vehicle model with an outdated radio. Either a modern radio must be purchased that has a USB port or Bluetooth, or the much cheaper alternative is resorted to and the stream is transmitted to the radio with an FM transmitter. 

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Frequently Asked Questions: FM Transmitters

What is a FM Transmitter?

An FM transmitter is a mini transmitter that transmits any audio signal to an FM frequency. This makes it so popular for use in one’s own motor vehicle, since on the one hand, an older radio without modern connections does not have to be removed and replaced, and on the other hand, complete connectivity with the smartphone is possible in the test.

The FM transmitter is able to transfer music from other devices, including MP3 and MP4 players, to any radio. Basically, all modern media can be used without the need for a cumbersome cable connection to the radio.

With good models, a crystal-clear sound is then also possible in the test and comparison, which makes listening a pleasure. The FM transmitter can be connected via the cigarette lighter, a USB cable or Bluetooth. Many models in the test and comparison are modern and sensibly designed, small and clear, with an illuminated display and a voltage display with voltmeter.

Some FM transmitters are stereo-capable and also have a built-in high-performance microphone, which in turn makes it possible to take calls while the music being played is automatically reduced in volume.

With an FM transmitter, you can listen to your favorite music in the car even without a jack plug or line-in input on the car radio. Other applications can also be used via the FM transmitter, such as the hands-free system or Spotify.

Calls received on the smartphone can be answered or rejected normally in the test, the music paused or the FM transmitter connected to the navigation system. Background noise is filtered out by noise suppression to ensure good sound.

The FM transmitter is usually attached via a bracket, can also be flexibly changed in position on many models. Some mounts can be rotated up to 360 degrees and offer a flexible neck to ensure the optimal viewing angle. Operation is possible via the display, a control panel, a remote control and via an app in the smartphone.

Devices that are able to show a memory function for the call list or song title display are also advantageous. The screen size is usually in the smaller inch range and allows the most important information.

While FM transmitters have been common in America for several years, they were banned in other countries until 2006. In the meantime, the purchase is also allowed if the FM transmitter has a CE marking and a transmitting power of 50 nanowatts ERP. This is sufficient for a few meters as bridging and does not interfere with other devices.

The transmitting power can also be amplified by manipulation, e.g. by using a piece of wire that serves as an antenna. However, this procedure is still prohibited. The radio signals of other transmitters and foreign sources also have an influence on the quality of the sound.

How does a FM Transmitter work?

To use an FM transmitter, you always need a free frequency on which no radio station is running in the test and no program is being broadcast. FM transmitters use the same frequency ranges as the radio stations and accordingly forward audio signals via the FM radio to an installed car radio.

This is only possible for a certain environment, as the range and transmission power are always limited. However, this does not have to be a disadvantage, as interference or noise can be noticed very quickly and can be compensated for by switching.

The FM transmitter is used with an available free frequency in the range between 87.5 MHz and 108 MHz. This is tuned with the same frequency of the radio. Depending on the power of the equipment, the transmission power can be between 5 to 30 meters, but is greatly reduced inside the vehicle.

Influence also have large cities and metropolitan areas, which have a very dense frequency of radio stations. The transmission is then hardly possible without noise and interference, but can always be influenced with appropriate settings.

If a free frequency is found, the sound is relatively free of interference. Nevertheless, there can be shifts in the changing positions, so that the own music signal is again overlaid by other radio stations.

The transmission power becomes more stable when connected with a USB cable or Bluetooth. The cigarette lighter, a rechargeable battery or batteries serve as a power source. More advanced FM transmitters are capable of reading USB storage devices in the test and have a USB port themselves. This makes them an excellent charger for other devices as well.

What frequency range can be used with an FM transmitter?

The free frequency in the test is 87.5 MHz. This is just before frequency that the first official radio station normally uses in comparison. But the frequency ranges below the VHF II band are also used rather less, so they are freely available and rarely cause interference when listening to the radio.

Accordingly, areas of report radio between 84 MHz and 87.5 MHz, areas of operational radio and radio applications of the BOS are available. It is possible to operate within the bandwidth of 87.5 MHz to 108 MHz. However, the use also depends on the FM transmitter itself in the test. Inexpensive models only guarantee a fixed frequency.

Types of FM Transmitters

FM transmitters are available in a wide range and differ in various features and attributes, especially in power, range and connectivity. There are models that are wireless and run on battery power, FM transmitters that are powered via the cigarette lighter and models that offer USB or Bluetooth in the test and comparison.

FM transmitter with free frequency selection

The typical FM transmitter can wirelessly transmit the music stream from external devices to the car radio and, to compensate for interference, allows a selection from all available frequency ranges between 87.5 MHz and 108 MHz.

Often, modern devices in the test and comparison are equipped with a USB port and can then be charged very quickly. There is usually also a choice of between 2 and 5 playback modes, e.g. for transferring music from smartphones, from a TF card or a Bluetooth adapter.

FM transmitter with fixed frequency

In addition to the commercially available FM transmitters, there are also cheaper versions that are only suitable for a specific and preset frequency range. A selection is not possible here, but becomes problematic for other countries, including Switzerland, since in this country only the use of FM transmitters is permitted that can transmit all frequencies between 87.5 MHz and 108 MHz.

FM transmitter with hands-free system

A further development are FM transmitters in the test and comparison, which have a microphone and therefore also allow the hands-free function on the smartphone. The operation is easier, can be done directly on the device via a button, for example, to accept or reject the call.

An FM transmitter with hands-free function is usually stereo-capable, so that it is then easy to switch from the status of the actual music playback to the reception of the phone calls.

Bluetooth FM Transmitter

Direct transmission with Bluetooth simplifies the applications even more. In the meantime, the offer of Bluetooth devices, which nevertheless do not cost too much, predominates on the Internet

In the test and comparison, the models show upscale features, an illuminated display that partly also shows the frequency range, incoming calls or the respective music track. Bluetooth is possible without cabling, but requires a device that is also suitable for Bluetooth.

How are FM Transmitters tested?

FM transmitters are tested in a test and comparison for their functions, features, performance characteristics, for their attributes, advantages and disadvantages. This is the case with each individual device, but also in the direct comparison of all competing products. From this, a best list can be determined, which also presents a price and comparison winner at the same time.

Design, Size & Quality

Among the FM transmitters there are very modern and high-quality devices, which also convince with a clear and sensible design. In the test and comparison, size, weight, design, appearance and workmanship are therefore evaluated, as well as attributes such as an illumination of the display or the buttons.

Display & Ease of Use

Many FM transmitters are nowadays available with a display, which not only makes it easier to operate, but also allows all important data to be read. Advantageous in the test is the display of the frequency ranges, the song titles and the song runtime, the volume and the battery operation.

Most of the time, there are also a few buttons and knobs available for direct switching. Devices that can also be programmed and adjusted via app or remote control are convincing in the test and comparison.

Suitability & Compatibility

The formats for which FM transmitters are suitable differ. The very plain devices are only suitable for MP3, newer models in a test and comparison for MP4, WMA, A2DP, FLAC, WAV and USB. The prerequisite for the better models in a test and comparison is a modern technology, including with USB connectivity or Bluetooth, with hands-free function and SD card connection.

Accessories, Functions & Battery

The range of functions in many FM transmitters is large in the test and comparison, with a good selection of necessary application options. This includes noise suppression via CVC technology, the hands-free function, RDS, an internal memory and a wide range of adjustable frequencies.

For models with a rechargeable battery, the performance, runtime and recharging behavior are checked in the test and comparison. Many models draw their power from the cigarette lighter. FM transmitters are available with or without audio cables as accessories.

Installation & Connection

The FM transmitters are tested and compared in terms of how easily and quickly they can be integrated and installed in the car. The connection is usually very simple. First, the bracket is screwed or attached, then the transmitter is placed in the bracket.

The radio is turned on, the connection is made, and the desired frequency range is set on both devices. The FM transmitter should work in the test if the same frequency is reached and a free frequency range is found.

Mounting & Alignment

In the test and comparison, FM transmitters with a modern mount that can also be rotated to ensure an optimal view of the display are rated positively. However, stability is more important. The transmitter should not slip out in the test, the mount should not tilt in an undesirable direction or come loose completely. During the drive, the grip should be given at all times.

Frequency Settings & Sound

FM transmitters offer either a preset frequency range or in modern form then the freely available between 87.5 MHz and 108 MHz. What is tested is how the sound shows up in different areas, what interference occurs and what changes are seen in congested areas. Many models are very powerful and have a good range and transmission.

What do I need to consider when buying an FM transmitter?

Of course, most people prefer a powerful device with good range and fast connectivity. In the test, the problem-free installation in the car and the possibility of using all available functions are important. The only thing that should be taken into account is that the device is permitted and approved in the user’s own country.

There are fewer problems as long as the CE mark and the effective transmission power of 50 nanowatts are present. Higher requirements in the test concern the reliable transmission of an interference-free sound. The sound can be influenced by the following purchase criteria:

Frequency Ranges

The more frequency ranges that can be selected in the test for an FM transmitter, the easier it is to find a free transmission slot and listen to your own music without interference. Preset frequency ranges are impractical and usually overlapped. Therefore, the spectrum should be as wide as possible and easy to adjust.

Connection Type & Connection

The FM transmitters work with a jack plug, with USB or with Bluetooth. Depending on which connection is preferred, a wide range of models can be found in stores, with Bluetooth devices holding their own in the comparison. Bluetooth is of course particularly suitable for use with the smartphone, as the devices all have an interface.


The range is not always specified by all manufacturers, but can be found by taking a closer look at the product information. This determines how interference-free the device can work and should be considered for the purchase of an FM transmitter in any case.

A range of between 5 and 10 meters is good. In the vehicle at least 3 meters must be possible. A too high range, on the other hand, is not necessary and can, on the contrary, interfere with other transmitters in the same environment.

Permissible range is 10 meters in the outdoor area, which harmonizes perfectly with the radiated power.

FM Transmitter Alternatives

An FM transmitter is a relatively inexpensive device in the test and comparison and remains one of the best solutions to ensure sound transmission from external devices on the radio. Alternatively, there is of course a cassette adapter for very old radios in the test, but they are not without cables and are generally outdated.

A USB transmitter or the use of typical Bluetooth devices is better. However, the latter also needed a radio that is suitable as a Bluetooth receiver.

The transmission is more stable in the test and comparison, since the FM transmitter sends an analog signal, while a digital signal is sent with Bluetooth. Nevertheless, interruptions can also occur with Bluetooth, which are not noise, but often result in error correction due to the transmission of individual packets, so short delays can occur.

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Last product update on 2022-09-29 | Source: Amazon Affiliate