How has radio handset technology evolved? A lot of people will have a lot of questions about this, the following to tell you about these problems.
1. Simple FM transmission and reception
At that time, in order to get rid of the shackles of microphone cables, people thought of the transmission and reception principle similar to FM broadcasting, that is, the use of the microphone's energy exchange principle and audio → modulation → amplification → transmission, and then through the FM radio or special receiver (special frequency point) to receive and play. In terms of sound quality, stability, anti-interference ability, etc., it can not meet the actual use requirements.
2. FM transmits and receives quartz oscillations
Because the use of electronic circuits to produce RC or LC oscillation, the stability of its oscillation frequency is greatly affected by the environment, its frequency is not too high, generally in two, three hundred megahertz below, in such a frequency band, extremely susceptible to other signals interference, at this time there is a quartz oscillator of the transmitting and receiving circuit. As we all know, the oscillation frequency of quartz crystal is very stable, the wireless microphone transmitter and receiver composed of it, the work is more stable, and its working frequency can be in the V segment (30MHZ-250MHZ), U segment (200-1000 MHZ), the external interference signal is not serious, and the use of wireless microphone brings better results.
In practical applications, because the oscillation frequency of the quartz crystal is not adjustable, so for a set of wireless microphones, its receiving and transmitting frequency is fixed, and requires one-to-one correspondence, if there is interference at a certain point in this frequency, it can not be used.
3. Use PLL to receive wireless microphones
PLL is the abbreviation of the English acronym of frequency phase locked loop. When the wireless microphone receives the transmitted signal, the frequency synthesis method is used to receive a satisfactory signal in a frequency band, and the working channel can be arbitrarily switched in the frequency band. In theory, in the 24 MHZ band, if the channel resolution is 1 MHZ, you can switch 25 channels; If the frequency is 125 KHZ, 193 channels can be switched, and the number of channels is related to the receiving frequency and channel resolution. Practical, to consider many aspects of the factors, however, the use of PLL technology wireless microphone, the receiving channel can be adjusted, and not just one, so that the use of more flexible, the transmitter and receiver can also be any combination, only in a bandwidth range of the working channel can be switched at any time to avoid interference.
Now, the first wireless microphones on the market have been eliminated and are only used in general trials. The other type also exists only in mid-to-low grade products or old products, and a large number of wireless microphones using PLL technology are used.
4. Diversity reception
Because the wireless microphone is the frequency modulation technology, its working frequency band in the V, U segment, the radio waves are straight line propagation, in the encounter of obstacles, will only reflect, not diffraction. Resulting in a shadow or dead Angle, affecting the use of the microphone effect (sound and light, frequency modulation noise, etc.), in order to avoid this situation, the current high-end wireless microphone, the use of diversity reception technology, the so-called diversity reception, that is, in a system need to have two identical receiving devices, a transmitter issued by the signal, at the same time by two FM receiver after identification and low frequency amplification, Respectively added to the merger, the merger is actually a selector, in each instantaneous selection of a strong received signal as the output signal, can effectively improve the receiving effect.