Stereo PLL FM transmitter

This is the latest BH1417 FM Transmitter design from RHOM that 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 4-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. Frequency selection is very straight forward. Simply select transmission frequency at which you would like to transmit, set the combination for 4-DIP switch and BH1417 will immediately tune to that frequency. If you can't hear the transmitted audio signal on your FM receiver then re-adjust 2.5 turn variable coil until you can hear the signal. As a test to see how PLL is working you can use a laboratory power supply to vary the voltage supply from 4 to 6V. While doing that BH1417 will automatically vary the voltage for MV2109 varicap diode making sure that there's no frequency drift.

The BH1417 FM Transmitter is a sophisticated device designed for efficient FM radio transmission. It incorporates several key features that enhance its performance and usability. The pre-emphasis circuit optimizes audio quality by compensating for high-frequency losses during transmission, ensuring a balanced sound output. Additionally, the built-in limiter maintains consistent audio levels, preventing distortion during dynamic audio playback.

The stereo encoder allows for high-quality stereo transmission, while the low-pass filter effectively eliminates unwanted audio signals above 15 kHz, which could lead to RF interference. This filtering is crucial for maintaining the integrity of the transmitted signal and ensuring compliance with FM broadcasting standards.

The phase-locked loop (PLL) circuit is a standout feature, providing stability in frequency transmission. This eliminates frequency drift, a common issue in less sophisticated transmitters. The integrated FM oscillator and RF output buffer further enhance the transmitter's reliability, allowing for a solid output signal.

Users can easily select from 14 different transmission frequencies in 200 kHz increments using a 4-DIP switch. The lower band frequencies range from 88.7 MHz to 89.9 MHz, while the upper band frequencies extend from 107.7 MHz to 108.9 MHz. This flexibility allows users to find a clear frequency for their broadcasts.

The BH1417 operates on a voltage supply of 4 to 6 volts and has a low current consumption of approximately 30 mA, making it energy-efficient. It delivers an output RF power of 20 mW, which is suitable for short-range transmission. With a channel separation of 40 dB, the BH1417 offers decent performance compared to older models like the BA1404, which provides slightly better separation at 45 dB.

For frequency tuning, users can adjust a 2.5-turn variable coil to ensure optimal reception on FM receivers. Additionally, testing the PLL functionality can be performed by varying the supply voltage between 4 and 6 volts using a laboratory power supply. During this process, the BH1417 automatically adjusts the voltage to the MV2109 varicap diode, maintaining frequency stability throughout the voltage range. This feature is particularly useful for engineers and hobbyists looking to evaluate the performance of the PLL circuit in real-time.This is the latest BH1417 FM Transmitter design from RHOM that 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 4-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.

Frequency selection is very straight forward. Simply select transmission frequency at which you would like to transmit, set the combination for 4-DIP switch and BH1417 will immediately tune to that frequency. If you can't hear the transmitted audio signal on your FM receiver then re-adjust 2.5 turn variable coil until you can hear the signal.

As a test to see how PLL is working you can use a laboratory power supply to vary the voltage supply from 4 to 6V. While doing that BH1417 will automatically vary the voltage for MV2109 varicap diode making sure that there's no frequency drift.

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