First, the transmitter power
Frequency modulation transmitter, the instantaneous frequency of the FM carrier with FM modulated signal changes such as wave amplitude wave, and its maximum power is equal to the average power; AM Built transmitter is amplitude modulated signal, when mAM = 1, the maximum transmit power is equal to the average power (carrier power) four times the AM transmitter FM transmitter final stage of the selection of the same type of power tube, according to the maximum power budget, FM transmitter emits power AM transmitter transmitter the average power of 4 times.
Second, anti-interference function
FM FM primary strengths of its strong anti-interference function is called anti-jamming, the first is greater than the amplitude modulation refers to the output of signal-to-noise ratio of the input signal to noise ratio (referred to as the signal-to-noise ratio S / N) under the condition, the FM receiving machine Admission of machine output of the signal-to-noise ratio.
FM than AM made strong anti-interference function of reason to analyze the transmitted signal power size from the standard two. Side of the FM wave frequency weight of power from the carrier power equally. The modulation coefficient MFM is bigger, its side frequency not only the number, and the ups and downs increased, which means the carrier power transformation for edge frequency power share large, edge frequency and amplitude modulated wave power is only equal to half of the carrier power (when the modulation Index MAM = 1). Thus, the FM Bobby amplitude modulated wave can have a greater section of the frequency power, which means it is also in order to overcome the noise and interference in the channel or inside the machine.
Secondly, accepted the mediation of the signal from the comparison and analysis of. Because the FM signal information is contained in the amplitude of the amplitude modulated signal proportional to the amplitude of the change in amplitude with a modulation signal (), amplitude modulated signal and demodulation of the envelope detector (also called an amplitude detector) is unable to inhibit parasitic AM interference; is included in the change of the instantaneous frequency of the high frequency vibration, and therefore, the interference caused by parasitic amplitude modulation can be removed through the slicer (or Limiting effect the share frequency discriminator).
Thus, whether from the edge of the transmit signal frequency power from the accepted signal demodulation analysis, frequency modulation anti-interference function better than the AM system.
Third, the AM transmitter power amplifier tubes stringent demand
AM transmitter wave modulated signal with the ups and downs of change, which reverse voltage of the amplifier tubes have a higher demand, should use a higher breakdown voltage tube or the tube is susceptible to breakdown and FM transmitter job amplitude state, the tube is not easy to breakdown.
Third, the width of the frequency band occupied by
Because broadband FM system occupied frequency bandwidth, FM is only suitable for use for medium and long-wave band, the selection of AM or single-sideband modulation method above in the VHF band.
Fourth, the production cost is relatively
Its commissioning process produced FM series equipment is appropriate and messy, so demand for the precious fruit of commissioning of equipment comprehensive parametric tester, shielded room equipment, commissioning equipment stability direct product of the resolution function, but also demand for professional and technical workers. Produced amplitude modulation equipment relatively convenient, so production of the the FM product of the threshold is much higher than produced by amplitude modulation products, and thus both the difference in the cost of production more than doubled.
After the above analysis of both the function and capital, users will have to know the situation of the two, is currently widely used in AM mode transceiver components, because of its cost-effective production with more convenient, and thus the demand for some not too high occasions, use this form.
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