Comparison Roidmi 2S vs Telefunken TF-FMT19BT

The FM frequency range supported by the FM transmitter.

For normal use of the device, it is necessary that at least part of this range coincides with the tuner range in the car radio, and that there is no full-fledged FM station broadcasting at the selected frequency. However, most modern FM transmitters cover frequencies of the order of 88 – 108 MHz, this is quite enough to find a suitable frequency.

The presence of a display in the design of the FM transmitter.

Various additional information can be displayed on the display : the set frequency, the signal source used, the name of the song being played, etc. This greatly simplifies device management.

Wired audio input, usually in the form of a standard 3.5mm mini-jack. The line-in (Aux) input can usually be output from a normal headphone output on a mobile phone or other similar device. And in some models of FM transmitters for linear connection, even their own wire with a 3.5 mm plug can be provided, which eliminates the need to use third-party cables.

The presence of a hands-free function in the FM transmitter.

The speakerphone implies the presence of Bluetooth (see the relevant paragraph) and allows you to conduct conversations by broadcasting the voice of the interlocutor through the car's speaker system. This is the best option for talking on the phone while driving — the phone does not need to be held in your hand, and the audibility is better than from the device's own speaker.

At the same time, it is worth noting that the presence of Bluetooth in the FM transmitter does not mean the presence of this function, it requires the presence of a microphone. However, there are also transmitters without a microphone. In one case, in order not to make the conversation public when there are other people in the salon; in the second case, for models without Bluetooth at all.

The presence of a remote control in the scope of delivery of the FM transmitter.

The ability to control the device from a distance is convenient, first of all, for passengers in the rear seats — for the driver, the remote control on the steering wheel is more relevant (see below), and the “navigator” in the front seat can easily reach the transmitter itself.

A slot that allows you to install memory cards in the FM transmitter and play music from them. Most often, card readers are made for SD or microSD form factor cards; however, both varieties have several variations (SDHC, SDXC), so before using such a transmitter, it's ok to clarify which varieties the card reader is compatible with.

File formats supported by the FM transmitter.

Almost all models support the MP3 format, which is the most common modern digital audio format. Some devices are also capable of working with WMA — this is also one of the main formats, but for a number of reasons it is used much less often. And even less common is compatibility with WAV — this format provides higher sound quality, but with FM broadcasting this advantage is lost, and the files themselves take up noticeably more space than MP3 and WMA.

The transmitter has a specialized USB port for charging smartphones, tablets and other external devices.

Note that you can also charge external devices from conventional USB connectors; however, specialized ports provide higher power output, which can significantly reduce charging time. It is also worth mentioning that the specific purpose of such a connector can be different: in some models it works only as a power source, in others it can also be used to connect USB drives. Many FM transmitters have two USB ports — regular and charging; this allows you to simultaneously charge an external gadget and listen to music from a USB flash drive. And in modern devices, the old USB A form factor is supplemented by a modern USB-C port.

The ability to change the angle at which the transmitter housing is located relative to the cigarette lighter socket. This function is realized thanks to the swivel plug for the cigarette lighter. It allows you to choose the most optimal position of the device for a specific situation — for example, raise the transmitter if it prevents you from reaching the tray under the cigarette lighter.