How is a car radio made

Connect your mobile phone to your old car radio: These options are available

It used to be easy: while driving, you tuned in to the radio, inserted cassettes or CDs and listened to them. Nobody thought about playing digital music collections or even streaming from a cell phone. It was not until around the middle to the end of the 2000s that SD card readers, AUX inputs for jack plugs or more modern car radios with Bluetooth and USB were found in new cars. Current automobiles have meanwhile become full-fledged multimedia centers with either their own internet tariff including WLAN hotspot, multiple displays and more. You can get an idea of ​​this in our automotive connectivity test.

But not everyone who depends on a car has had the opportunity to afford a modern car in recent years. What if you want to keep your Spotify playlists up-to-date in your car or you just don't feel like burning your MP3 collection on CD-ROM anymore? We reveal what options you have to transfer your music from digital data storage media or your smartphone to the car radio and enjoy it via the built-in speaker system. Specifically, there are two options if you don't want to buy a new radio or a new car.

Connect mobile phone to car radio: Bluetooth, USB or AUX via accessories

The cheapest method of retrofitting a car radio with Bluetooth, USB or AUX input is with a so-called FM transmitter. FM stands for the frequency band of the ultra-short wave, from the English the synonym FM (for: frequency modulation) developed.

FM transmitter: what should you watch out for?

Usable devices are available for less than 20 euros; they usually get their electricity from the car's 12V socket. If this is missing, transmitters, which you connect to your smartphone using a USB or Lightning cable, can help. However, these are not recommended for longer car journeys. After all, music playback, Bluetooth streaming and various apps gnaw at the battery that you cannot charge with such a transmitter.

The car radio itself only needs to be able to receive the standard frequencies of the VHF range (between 88.1 and 107.9 MHz). Many devices go a little further in order to be able to use free frequencies more easily in a small area. Information on the frequency range is then, for example, "87.5 MHz to 108.0 MHz".

FM transmitter: this is how it works

An FM transmitter does nothing more than pick up signals from your smartphone via Bluetooth or jack cable or from a storage medium and pass them on via radio in a small area of ​​a few square meters. To do this, you select a frequency on the transmitter for which the car radio is then set to receive.

FM transmitter: what helps against noise and interference?

It is advisable to set a frequency that is not used regionally - otherwise there will be interference such as regular crackling, hissing or overlapping audio signals - from real radio stations or other users of FM transmitters in the vicinity. These disturbances are not to be confused with typical noises from the loudspeakers, which can be caused by active mobile phone reception when calling or downloading. Bluetooth 5.0 and positioning the cell phone as close as possible to the transmitter and the car radio can reduce this - but not always completely prevent it.

A tip for finding the optimal settings: On this Wikipedia list you can see radio stations and the frequencies used in Germany. Ideally, you set a frequency that is not used over a large area. You can also sort the table by location for a better overview. A text search ([Ctrl] + [F], or mobile via the menu) for your place of residence or the region is recommended for quick retrieval.

FM transmitter: These features are important

Incidentally, a hands-free facility can also be implemented with an FM transmitter. Make sure that the product is supported accordingly - a microphone must be available. Voice is then transmitted over the car speakers during phone calls.

Devices that have USB ports are recommended. In addition to media player functions for USB sticks or card readers, which you control via the transmitter, you can also charge your smartphone battery while it is in use. Modern fast charging functions should also be supported if required. As with other chargers, make sure that the outputs have a sufficiently high amperage, otherwise Bluetooth transmission, audio playback and, above all, streaming will eat away at the battery more than the transmitter can recharge it.

In this way you avoid the situation of standing still after long car journeys without a smartphone. Around 2 amps of current and upwards (per device, at 5 volts) are sufficient for current mobile devices, below that you should not expect too much from the charging current. If two devices are to be charged, the value is divided accordingly. Use the information on the charger for your smartphone as a guide.

Which FM transmitters are worthwhile?

One example is this FM transmitter on Amazon. It has two USB ports that deliver up to 2.4 amps - including Quick-Charge 3.0. Hands-free calling is supported, as is Bluetooth 5.0. You also get a card reader and the extended frequency range. According to our practical test, the sound sounds "full", not tinny or slimmed down, and is only slightly inferior to that of an MP3 CD with pieces of music with an average bit rate (192 to 256 Kbps), for example. The wired control design is intended for cars where the 12V connection is a little more "hidden". However, the control element is glued to a flat surface. Alternatively, you can combine it with one of the following brackets in a smaller format.

Buy NowBluetooth 5.0 FM Transmitter, SONRU Bluetooth Auto ...

There are good reviews from reviewers for the following FM transmitter. It also offers Quick-Charge 3.0, Bluetooth 5 and the extended frequency range. There is also a hands-free function and of course buttons for media control. It has a sleeker design and works well when the 12V connection is easily accessible.

Buy Now ZeaLife Bluetooth FM Transmitter, Car Radio ...
17,99 €

In addition to Bluetooth and USB (optionally with media player functions), there are also FM transmitters with a jack input - recognizable by terms such as "AUX" in the product name. This is interesting for vehicle occupants who do not have Bluetooth - such as old MP3 players. Cable entries are now less common. In addition to more and more smartphones that do not have a jack connection, this is one reason: you no longer have to prefer a cable to Bluetooth technology. Audiophile drivers shouldn't be too demanding when using FM transmitters. The Bluetooth connection of current devices is usually not the reason for poor sound and is no longer objectionable.

The greatest loss of quality is caused by the transmission through radio technology. Check user reviews to see how good the sound quality transmitted by the transmitter is. Are there general distortions at certain frequencies or even background noise? Can the reason be ruled out that the user set too closely “adjacent” transmitter frequencies? If the transmitter does its job well, the audible difference for the average consumer is very small. Of course, don't be blinded by the overly positive statements from reviewers.

FM transmitter with AUX connection

Anyone looking for a transmitter with a jack input (AUX-in) that does well in reviews could take a look at this FM transmitter on Amazon. In addition to the cable entry, it also offers two USB ports (total 2.4 amps) including power delivery.

Buy nowBovon Bluetooth FM Transmitter with Dual Microphone, ...

Mobile phone in the car: ideal mount

If the smartphone is the source of music, a mobile phone holder proves to be particularly practical - if you don't already have it because of navigation apps. The aftermarket is huge. There are brackets with a clamping mechanism or magnet, among other things. With the latter, you usually have to glue a metal plate to the back of your smartphone.

The brackets themselves can be attached to the inside of the windshield using a suction cup. For magnetic solutions there are often clamps that you attach to the air outlets of the air conditioning system. The following brackets and products are recommended.

Buy NowWicked Chili Car Holder with Ball Joint ...
Buy NowSyncwire Magnetic Car Cell Phone Holder, 360 Degrees ...
12,74 €

The Wicked Chili holder is compatible with almost all current smartphones that are no wider than 74 millimeters. Even common cases are not a problem. There are adjustable shelves for access to the charging port. You can then turn your fixed smartphone as you like or position it at the right angle thanks to the joint head.

Important: In contrast to the second magnet solution with a clamp, you have slight restrictions in view of the suction cup solutions. So position the gripper arm and smartphone in such a way that your forward view from the windshield is affected as little as possible.

The magnetic holder is practical because it is particularly handy and inconspicuous. Smaller smartphones hold by themselves. The magnets supplied help with large devices. Horizontal and vertical operation is possible, as is free positioning using the swivel head.

Note: With brackets for fans, pay attention to the shape of your ventilation outlets in the car. The model shown is recommended for standard ventilation outlets with right-angled grilles. If your car has round openings or grilles for ventilation, pay attention to information about the compatibility with the respective manufacturer or car model in the case of brackets.

Connect mobile phone to car radio: AUX and USB via conversion

Another way to connect your mobile phone to the car radio is to convert it. However, you should only do this in consultation with your dealer or car dealership, whether you have any guarantee or warranty claims. To be on the safe side, we emphasize that such work is carried out at your own risk. We can therefore only recommend them to experienced hobbyists.

Depending on the manufacturer and the installed car radio, interfaces for AUX or USB may already be available. These would only have to be made accessible in the passenger compartment. The conversion is therefore not available to all users. As a rule, USB and AUX can be retrofitted in this way.

Since we cannot give general recommendations for all cars here, we refer you to your vehicle documents and instructions. Find out which radio was installed by which manufacturer. Blaupunkt radios are often found in older VWs. Bose can provide the sound for old luxury cars from Audi. There are not always options for retrofitting. Informing them if you do not want to use an FM transmitter does not do any harm.

With the search engine you trust and the exact radio name, which you can add search terms such as "retrofit USB" or "retrofit AUX", you can find various instructions and tutorials online. They are much better tailored to your individual vehicle characteristics than we could generally explain here.