The Operation Principle of Two Way Radio
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.
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.
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
CPU generates CTCSS / DTCSS signal that was magnified and adjusted then, and enter into the voltage-controlled oscillator for modulation. After receiving the low frequency signal obtained by frequency discrimination, part of them process filter shaping through the amplification and band-pass filter of sub-band, then enter into the CPU, compared with the preset value, and the results will control the audio power amplifier and speaker output. That is, if same as the preset value, the speaker will turn on, and if it is different, the speaker is will turn off.
Using radio will have radiation problem or not
Radio design conforms with the relevant provisions of the  869 document issued by the Ministry of Information Industry , which will not harm the human body. Moreover, when using radio, it is not close to the human body, but away from the human body 5 to 7 cm.
Belows are several factors of affect radio’s conversation distance and effect
1）The stronger the transmitter output power, the greater the coverage of the transmitted signal, the farther the communication distance. But the transmission power can not be too large, if it is too large, not only consuming electricity and impacting life of power amplifier components,also the interference is stronger, which will affect others communication effect. The larger transmission power also can produce radiation pollution. The regulation and administration of radio-services agency of every country has clear stipulation on the transmission power of communication device.
2）The higher the receiver sensitivity of the communication device, the farther the communication distance.
3）Antenna gain, when antenna match with radio , usually, the antenna height increases, the receiving or transmitting power enhance. Hand-held radio’s antenna always is helical, the bandwidth and gain is smaller than other types of antennas, and is more likely to influence by human impact.
Environmental factors mainly have path, the density of trees, the environmental electromagnetic interference, buildings, weather conditions and terrain differences and so on. These factors and other parameters directly affect the electric field intensity and coverage area of signal.
3、Other Influence Factors：
1）Low battery power. When battery power is low, the conversation quality will get worse. When the problem gets more serious, it will make noise and affect the normal conversation.
2）Matched antenna. When antenna frequency band is inconsistent with radio band and antenna impedance not match, they will seriously affect the conversation distance. For users, the antenna should be tightened when using it. Besides,users can not freely use the antenna that provided by non-manufacturers,or antenna frequency is different with radio.
3）Tone quality is mainly determined by the pre-emphasis and de-emphasis circuit, there are more advanced voice processing circuit "applications of voice companding circuit and low-level expanding circuit", which have high fidelity effect on voice.
4) Factor of affecting the distance and effect of two way radio is also related to the season, summer is better than winter.
Professional radio generally use a very good performance of the plastic material PC + ABS, which have good luster appearance and not easy to aging and wear, so make the products durable ; commercial radio always choose engineering plastics ABS, which can perfectly satisfy the requirements in appearance, strength, wear resistance and aging; keypad with silica gel have characteristics of wear resistance, non-aging and good hand feeling; aluminum housing with lightweight aluminum alloy ADC12, is easy to shape and subsequent processing.
Generally include housing,PTT button, headphone and power jack plug, PCB components, LCD parts, volume / switch button, coding knob, indicator, MIC and so on. Function of PTT button is to transmit switch, generally on the side.Indicators indicate the operating status, usually at the top. The top of radio also has volume / switch button and coding knob (select channel). LCD parts visually display the working status of radio. PCB components are the core of radio, the important components are on the PCB, non-professionals not allow to disassemble. Due to the requirements of technical performance and anti-drop , most of the radios have special shield, aluminum (fixed PCB) and so on. Besides, Professional radio have waterproof requirements and more complex structure.
The battery is divided into Ni-Cd, Ni-MH and Li-ion batteries with capacities of 600mAh, 800mAh, 1100mAh, 1500mAh and so on. Li-ion battery costs are more expensive,so is still under the development stage. Ni-Cd and Ni-MH battery is more common, generally the large-capacity battery is recommend to using Ni-MH battery . Surface and the bottom shell are used ultrasonic welding, so they are solid and reliable.
The function is to fasten radio on the leather belt. To make it easier for consumers, belt clip can be detachable.
Divided into two parts of the antenna jacket and antenna core. Antenna jacket uses the high-performance TPU material, which have good performance of anti-bending and anti-aging ; antenna core generally uses thread construction and connects with the host, which is easy to disassemble.
Together with AC adapter to charge the battery or the whole radio. It’s Structure generally include DC socket, charging shrapnel, indicator light, keypad and so on. DC socket connects with the AC adapter, shrapnel connects with battery pole piece, indicator light indicates the charge status, the keypad is played the role of discharge. Desktop Charger generally can charge the battery and the whole radio.
7、In addition，the two way radio also have leather case and headphone and other accessories.