Interphone Operate Principle And Function Introduction

The electromagnetic spectrum is the sum of all frequencies of electromagnetic radiation, ranging from the longest radio waves to the shortest cosmic rays. The spectrum can be divided into parts, called frequency bands. The electromagnetic spectrum is divided into the following frequency bands:

 100Hz 300KHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz

 AM:Amplitude Broadcasting          MW:medium wave          SW:Shortwave          HF:high frequency

 VHF:Very High Frequency          UHF:Ultra High Frequency          SHF:Super High Frequency          EHF:Extremely High Frequency

 Interphone use of the band:

 VHF 136-174MHz is divided into two sections: 136-150MHz, 150-174MHz

 UHF includes 350-370MHz, 370-390MHz, 400-420MHz, 450-470MHz

 Radio frequency band characteristics:

 The atmosphere around the earth will attenuate and refract radio signals, as it attenuates and refracts light. The usual rule is that the lower the frequency, the smaller the attenuation loss is: Ground wave propagation (radio below 300KHz (30MHz-900MHz most suitable for wireless walkie-talkie communication) Noise: electromagnetic noise from the machine and the engine, because the noise signal (the frequency range of the radio frequency of the radio frequency) The frequency of low-frequency signals, therefore, the low-frequency signal is more sensitive to noise.Transfer distance: in rural and suburban VHF transmission distance of the largest urban UHF transmission distance in the largest.

Principle Overview:

 1、Transmitter：

Phase-locked loop and voltage-controlled oscillator (VCO) generate the transmitted RF carrier signal, after buffer amplification, excitation amplification and power amplifier will generate the rated radio-frequency power, which using the antenna low-pass filter to suppress harmonic components, then transit through the antenna.

2、Receiver：

Receiving part is the dual frequency conversion super-heterodyne mode. The signal inputted from antenna will magnify radio frequency through the transceiver conversion circuit and the band-pass filter, then through a band-pass filter into a mixing frequency, which mix the amplified signal from the radio frequency with the first local oscillator signal from the phase-locked loop frequency synthesizer circuit at the first mixer and generate a first intermediate frequency signal. The first intermediate frequency signal further eliminates the clutter signal of the adjacent channel through the crystal filter. The filtered first intermediate frequency signal enter into the intermediate frequency processing chip, then mix again with the second local oscillator signal to generate the second intermediate frequency signal, which filter unwanted spurious signals through a ceramic filter, then it was amplified and frequency discrimination to generate audio signal. Audio signal go through the amplification, band-pass filter, de-emphasis circuit, enter into the volume control circuit and magnify by power amplifier and drive speakers, then get the information people need.

3、Modulating Signal and Circuit:

The human voice convert to the audio signal by microphone, which enter into the voltage-controlled oscillator and modulate directly through amplifying circuit, pre-emphasis circuit and band-pass filter