For a long time, when model friends mentioned the anti-interference performance of proportional radio remote control equipment, it was generally believed that frequency modulation (FM) equipment was better than amplitude modulation (AM) equipment, and equipment manufacturers also positioned AM equipment on the low-end products of 27MHz dual-channel primary vehicles and ships. This inadvertently strengthened the impression in everyone's mind. In fact, this concept is wrong! Or at least outdated old ideas. First of all, let's talk about the origin of this view. As early as 1950s and 1960s, after the formal application of the first generation of command and remote control equipment, many athletes found that AM equipment was much worse than FM equipment in anti-interference performance, so the saying that AM equipment had poor anti-interference was widely circulated in the industry. In the words and deeds of model athletes and coaches from generation to generation, this concept has been deeply rooted and passed down to the proportional remote control era of integrated circuits and single-chip computers indiscriminately. However, if you pay attention, you will find that some maintenance and designers of remote control equipment do not necessarily agree with this view. In fact, it is not difficult to understand that in 1950s and 1960s, AM instructed remote control equipment to transmit amplitude modulation of carrier frequency through audio signals of each channel, and received audio signals of each channel to express the on-off state of each channel, and the audio signals of each channel were easily influenced by crosstalk caused by adjacent frequency interference, thus losing control. In addition, the equipment at that time used complex electronic tubes or transistor discrete components. In order to simplify the circuit and increase the remote control distance, most simple super regenerative receiving circuits are used, and the passband is too wide. To put it bluntly, it is similar to the current children's remote control toys. So it is not surprising that it often gets out of control. Let's talk about the current digital proportional radio remote control equipment. At present, AM equipment adopts the same time-division pulse width or pulse position coding method as FM equipment in coding circuit, and the difference between them is only the modulation method of carrier frequency. AM equipment adopts frequency amplitude keying mode: that is, by switching the high-frequency transmitting circuit, the switch tube is used to indicate the high and low level of the coded signal, that is, whether there is a high-frequency transmitting signal or not. In the receiving circuit, because the transmitter only sends out high-frequency signals with a single frequency, the receiving frequency range of the receiver can be made very narrow, making it difficult for other adjacent frequencies to pass. This is my narrowband receiving technology. Frequency modulation equipment uses the high and low levels of coded pulse to modulate the frequency difference of high-frequency circuit: that is, two frequencies are used to represent the 1 and 0 potential of the code. The frequency difference between these two frequencies is the frequency difference. In the receiving circuit, a frequency discrimination circuit is used to distinguish two frequencies. The frequency discriminator circuit is actually a frequency filter. The closer the signal is to its own resonant frequency, the higher the voltage induced when it passes through it. Because the transmitter sends out two kinds of frequency signals with frequency difference, high and low voltages are induced on the frequency discriminator to complete the restoration of the coded stream. It is not difficult to see that in this process, as long as there is a high-frequency signal adjacent to one of the two frequencies sent by the transmitter, it will lead to confusion in code stream recovery. That's out of control. Therefore, the wider the difference frequency of FM equipment, the easier it is for frequency discriminator to distinguish the level of coding: that is, the farther the remote control distance is, the worse the anti-near-frequency interference is. On the contrary, on the contrary. Therefore, the passband design of modern FM equipment should consider remote control distance and anti-interference. This is also an aspect of the performance difference between domestic and imported equipment. It is precisely because of the above reasons that AM equipment is not inferior to ordinary FM equipment in anti-jamming performance because the transmitter sends out a high-frequency signal with a single frequency, and the interference sources are less than FM equipment, and the narrowband receiving technology is adopted. On the contrary, AM frequency keying modulation reduces the chance of interference compared with FM equipment sending two signals with frequency difference. Moreover, because the modulation tube of AM equipment is in the state of intermittently controlling the operation of high-frequency transmission circuit, the transmitter of AM equipment is more energy-saving than that of FM. Imagine that if both AM and FM devices encounter continuous K interference waves with the same frequency, both AM and FM devices will be out of control because of the error stream of 1 or 0 output by the decoding circuit. This is also the reason why PCM/FM equipment is not spared. Therefore, it is not uncommon for some foreign 4-6 remote control equipment to be equipped with AM equipment. For example, a common attack in Shuang Ye-4 am. Moreover, the presence or absence of two state modulation modes for AM frequency keying high-frequency signals can be regarded as a special state after two frequencies of FM equipment enter the frequency discriminator, so AM transmitters in two AM and FM equipment with the same frequency can control FM receivers.