Abstract: This article uses an integrated IF voltage controlled oscillator (IF-VCO) to relay mobile phone audio signals to the FM broadcast band. Place the phone speaker near the microphone so that you can extend the car hands-free function for your phone while the user is driving. This article refers to the address: http:// The circuit shown in Figure 1 is capable of converting a mobile phone audio signal into an FM broadcast band. By bringing the speaker of the mobile phone close to the microphone, the user can hear the voice signal of the mobile phone by means of the car FM broadcast, thereby obtaining a car hands-free calling mobile phone. Figure 1. FM transmitter circuit with microphone to realize the hands-free calling function of the mobile phone. IC1 is an integrated IF-VCO with differential input that supports the entire FM frequency range from 70MHz to 150MHz. Inductor L1 is used to set the center frequency adjustment range of the VCO. Select the appropriate L1 and place the output frequency at 100MHz, depending on the effective inductance between IND and GND, which is the center frequency of the FM. The 270nH inductor guarantees an adjustment range of 97 to 128MHz. Subsequently, the RADJ resistance is adjusted so that the VCO matches the frequency of a certain FM channel. Resistors R2 and RADJ provide bias to the internal varactor. FM stations are separated by an odd multiple of 0.2 MHz. The VCO differential output provides -8dBm of power. The power measured at 3m from the source must be less than 250μV, as specified by the FCC for 47 CFR Part 15. The electret microphone is biased by R1, and the AC coupled microphone audio signal adjusts the VCO frequency by changing VTUNE. The VCO output frequency will follow the volume or amplitude of the microphone signal. This circuit works well with audio signals around 20mVRMS. Do not exceed the VCO adjustment range, otherwise the audio signal received by the FM radio will be completely distorted. In addition, exceeding the VCO adjustment range also reduces the power of the carrier signal because the transmit power is outside the effective spectral range of the receiver. In Figure 2, replacing the microphone and R1 with the phone's audio output port requires proper adjustment of the phone volume to optimize performance. If you can connect directly to the phone's audio output, it will help eliminate the background noise of the microphone. Figure 2. FM transmit circuitry with direct access to the audio input to help eliminate background noise from the microphone. LC Adapter makes two end face precision docking, which can make light energy from transmitter optical fiber coupled to receiver optical fiber efficiently and will reduce impact to a minimum because of intervention optical link of system. Fiber Adapter LC normally include single mode and multimode LC adapter, zirconia sleeve and bronze sleeve, simplex and LC Adapter Duplex. Hybrid Fiber Optic Adapter LC, such as female to male & male to male fiber adapters. Foclink provides LC Adapters with Standard and Premium two quality levels for choices to fully meet the different applications and requirements. LC Adapter LC Adapter,LC Adapter Duplex,Adapter LC,Adapter LC Duplex Foclink Co., Ltd , https://www.scfiberpigtail.com
October 30, 2020