50mW BH1417 Stereo PLL FM Transmitter

This is a high-fidelity stereo PLL FM transmitter designed for various audio sources including computers, sound cards, game consoles, CDs, DVDs, MP3 players, and stereo mixers. The board features two microphone amplifiers, enabling high-fidelity FM stereo radio transmission when paired with a compatible receiver. It is ideal for creating stereo wireless speakers, wireless microphones, wireless headphones, and other wireless audio adapters. The BH1417 integrated circuit from ROHM, a simple and practical solution, integrates a phase-locked loop circuit, a stereo encoder, and a transmitter circuit, alongside additional features. The pre-emphasis circuit, limiter circuit, and low-pass filter enhance sound quality, achieving a total harmonic distortion of 0.3%, stereo separation of 40dB, and an RF output level of 100dB. The BH1417F chip improves the signal-to-noise ratio (S/N) of the pre-emphasis circuit, preventing signal over-emphasis through the limiting circuit. The circuit includes a low-pass filter (LPF) to generate the stereo composite signal modulation and the PLL component for the FM transmitter. With excellent frequency characteristics, it achieves 40dB isolation, delivering sound quality comparable to local FM radio stations. The external power supply is filtered by a 78L05 5V DC regulator for the BH1417 chip. DIP switches M1 and M2 activate the dual microphone amplifiers, where the microphone (MIC1) converts sound signals into electrical signals sent through C3 to the microphone amplifier circuit composed of V1, R6, and R7, with volume adjustment provided by RP1 and capacitors C5 and C6 before reaching the BH1417. DIP switches D0 to D3 set the transmission frequency. The BH1417 outputs a stereo FM carrier signal from pin 11, which is coupled through C36 to a high-frequency power amplifier formed by V3, R21, L3, and C37, amplifying the signal before coupling through C38 to the transmitting antenna (ANT1). The BH1417 FM transmitter chip integrates multiple features in a compact package, including pre-emphasis, limiter, stereo encoder, low-pass filter to block audio signals above 15kHz, a PLL circuit for stable frequency transmission, an FM oscillator, and an RF output buffer. There are 14 selectable transmission frequencies in 200kHz increments, ranging from 88.7 to 89.9 MHz for the lower band, and from 107.7 to 108.9 MHz for the upper band. The BH1417 operates at 4 to 6 volts and consumes approximately 30mA, providing an RF output power of 20mW. It offers a channel separation of 40dB, which, while slightly lower than the 45dB provided by the older BA1404 FM transmitter chip, is still considered good. The BH1417 is available only in an SOP22 IC package, which may be a limitation for some users, but its smaller size allows for the entire transmitter to fit on a compact PCB. The BH1417 chip can also function as a standalone stereo encoder, offering flexibility in transmitter and amplifier selection. It retains essential functions like pre-emphasis, limiter, stereo encoder, and low-pass filter in a compact form, requiring minimal external components. The MPX output on pin 5 can be directly connected to an external FM transmitter via a 10µF capacitor. Frequency selection is straightforward; users simply set the desired transmission frequency using the 6-DIP switch combination, and the BH1417 tunes to that frequency immediately. If the transmitted audio signal is not audible on an FM receiver, further troubleshooting may be necessary.This is an excellent Hi-Fi Stereo PLL FM Transmitter, the audio source can be the computer, sound card, game consoles, CD, DVD, MP3, stereo mixer for stereo audio signal modulated emission transmission, the board also contains two mic amplifier, with the common receiver can achieve high-fidelity FM stereo radio FM stereo transmission. Suitable for the production of stereo wireless speakers, wireless microphone, wireless headphones, CD, MP3, DVD, PAD, notebook computer and other wireless audio adapter development and production. ROHM`s new Japan has BH1417 is one of the most simple and practical integrated circuits, which combines phase-locked loop circuit, stereo encoder circuit, transmitter circuit, as well as other additions.

Pre-emphasis circuit, limiter circuit and low pass filter can significantly improve the sound quality. The total harmonic distortion up 0. 3%, stereo separation to 40dB, RF output level is 100dB. BH1417F is an excellent new IC chip, this circuit improves signal to noise ratio (S / N) of pre-emphasis circuit to prevent signal over emphasized limiting circuit, the control input signal frequency low-pass filter circuit (LPF), generate stereo stereo composite signal modulation circuit, FM transmitter phase-locked loop circuit (PLL) component.

BH1417F excellent frequency characteristics, it can achieve 40dB of isolation, transmitted sound quality is similar to local FM radio stations. External power is filtered by 78L05 5V DC regulated output for BH1417 chip. DIP switches M1, M2 turn on dual microphone amplifier, microphone MIC1 the sound signals into electrical signals by the C3 sent by the V1, R6, R7 microphone amplifier circuit composed of enlarged RP1 adjust the volume by the C5 to C6 into BH1417 later by the left channel signal input.

DIP switches D0, D1, D2, D3 used to set the firing frequency. BH1417 Stereo FM carrier signal from the output of the first 11 feet, coupled by the C36 into the V3, R21, L3, C37 composed of high-frequency power amplifier, amplified signal coupled through C38 to launch transmitting antenna ANT1. BH1417 FM Transmitter chip includes a lot of features in one small package. It comes with pre-emphasis, limiter so that the music can be transmitted at the same audio level, stereo encoder for stereo transmission, low pass filter that blocks any audio signals above 15KHz to prevent any RF interference, PLL circuit that provides rock solid frequency transmission (no more frequency drift), FM oscillator and RF output buffer.

There are 14 possible transmission frequencies with 200KHz increments that users can select with a 6-DIP switch. Lower band frequencies start from 88. 7 up to 89. 9 MHz, and upper band frequencies start from 107. 7 up to 108. 9 MHz. BH1417 can be supplied with 4 - 6 voltage and consumes only around 30mA, providing 20mW output RF power.

BH1417 provides 40dB channel separation which is pretty good, although older BA1404 FM Transmitter chip provides slightly better 45dB channel separation. BH1417 is only available in SOP22 IC case so this may be an inconvenience for some folks. On the other hand, because the chip is smaller than regular DIP-based ICs it is possible to fit the entire transmitter on a small PCB.

BH1417 chip may also be used a stand alone stereo encoder. The advantage of that is that you have full freedom of using a transmitter & amplifier of your choice. You will still have a pre-emphasis, limiter, stereo encoder and low pass filter in one small package because very few external components are required for these blocks.

PIN 5 is MPX output that can be directly connected to an external FM transmitter through a 10uF cap. Frequency selection is very straight forward. Simply select transmission frequency at which you would like to transmit, set the combination for 6-DIP switch and BH1417 will immediately tune to that frequency. If you can`t hear the transmitted audio signal on your FM receiver 🔗 External reference