Who invented amplitude modulation

Because MPPSK is the multi-system modulation, thereby demodulation performance is certainly not as binary EBPSK modulation, and, when M is larger, demodulator also can be more complicated, especially be not suitable for multipath channel wavelength of medium wave channel is very long fortunately, almost can not consider Multipath Transmission. Therefore, after comprehensive balance, " condition is 2.

Wherein, A is the amplitude of multiplex modulated signal, the simulated audio signal as the complex modulated sideband, for the amplitude modulation by tone coefficient, both for preventing amplitude modulation, but the also power division between control simulation audio signal and digital signal; that it is expressed suc as formula 1 as the complex modulated carrier wave MPPSK modulation signal of replacing existing pure sinusoid carrier wave.

From Fig. But, the power amplifier level output of existing AM broadcast transmitter often is added with resonant tank, and as shown in Fig. This resonant tank is a band pass filter in fact, although the power spectrum that can make filtered hybrid multiplex modulation system transmit is " good-looking " more, as shown in Fig.

But, in order directly to utilize existing high-power AM broadcast transmitter, the present invention can only face this reality, and manages to alleviate or compensate its adverse effect in receiver.

Whole the theory diagram of receiver being broadcast receiver system as shown in Fig. Sinusoidal signal multiply each other and utilize band pass filter to take out frequency and be high intermediate-freuqncy signal carry out the intermediate frequency amplification.

For the IF-FRE near existing radio and television and communication products, in order to share various lots of standard components and parts on market, the high intermediate frequency of desirable receiver is thereby, according to formula 5 , the frequency range of local oscillator is. According to the content of relevant " MPPSK transmission system " in this specification background technology, should meet formula 4 when selecting the MPPSK modulation parameter as far as possible, get with , can eliminate the discrete line spectrum in MPPSK modulated signal power spectrum fully like this, for the interference of other broadcast station signal of the simulated audio signal of same channel and adjacent channel, can be lower.

By this condition substitution formula 3b , the transmission code rate that obtains the MPPSK modulation is. Visible, now code check is only relevant with carrier frequency and M. And, after carrier frequency is determined, the M value is larger, code check is lower.

According to the principle of formula 3d and in conjunction with emulation experiment, get final product to obtain the numerical value of required modulation parameter M, and the highest code check under corresponding carrier frequency.

Here we also require to guarantee the character rate of MPPSK modulation at least higher than the audio signal highest frequency. Therefore, even take out in actual applications half code check in the future, carry out chnnel coding, further to guarantee the reliability of system, we still can obtain the clean code check of The multiplex modulated signal of multiplier output, after the amplification of broadcast transmitter power amplifier and filtering, can be delivered to the upper externally emission of launching tower antenna , as shown in Fig.

Signal waveform and power spectrum before and after its filtering, respectively as shown in Figure 4 and Figure 5. Adopt local carrier signal with the reception signal multiplication, then through bandpass filtering, take out required intermediate-freuqncy signal, complete up-conversion process. Then give shock filter by the intermediate-freuqncy signal after amplifying. Therefore because people's ear is more responsive for the amplitude distortion of sound waveform, attempted adopting the impact of filter on audio signal of smoothly making a start of multiple filtering method.

Through experiment repeatedly with observe to find, the signal carrier frequency is placed on the transition band of the logical or high pass filter of band, can effectively improve the filter of making a start to the adverse effect of audio signal, promote the audio frequency demodulation quality. Thereby the present invention unites two into one both, adopt a shock filter to replace. Simulation shock filter during concrete emulation experiment in Fig.

The output of shock filter is divided into two-way: wherein a road is directly connected to an input of multiplier; And from another road extract with the carrier wave of the first via with homophase frequently output to another input of multiplier. In multiplier, by the DSB-AM multiplex modulated signal of impact filtering output and its local frequency of extracting, be intermediate frequency coherent carrier signal multiplication, carry out coherent demodulation owing to taking full advantage of carrier energy, therefore be expected to promote the demodulation performance to the audio signal of the digital signal of MPPSK modulation and DSB-AM modulation simultaneously further.

Now the output signal of multiplier is MPPSK impact filtering signal envelope and mix stack of audio signal, the two is complete aliasing on time waveform, also aliasing likely on frequency spectrum, therefore the present invention requires the character rate of MPPSK modulation high in the design of " complex modulated transmitter system ", at this, is exactly at least will be higher than the highest frequency of audio signal , so just can utilize different filters to extract respectively envelope and the simulated audio signal of MPPSK modulation impact filtering signal " code check territory " being still frequency domain in essence.

Therefore, the output signal of multiplier is divided into two-way again, and a road is for the demodulation of audio signal, and another road is for the demodulation of digital signal. Traditional amplitude modulation broadcasting broadcast receiver, used envelope detection to realize the demodulation of amplitude modulation by tone signal more, and this mode is without the phase place of utilizing carrier signal, thereby simple, cheap, uses till today always.

But the performance of this non-coherent demodulation mode is in theory not as coherent demodulation. Sound difference people ear for Fig. Therefore, as long as get in theory the high pass filter of low-end cut-off frequency higher than 4.

Although compare with Fig. A series of processing through front, just carry out digitlization function before this all can realize as crystal filter, ceramic filter etc.

For the MPPSK demodulator in Figure 10, we retain one section sequence of impacts after bandpass filtering at receiving terminal as related operation template or matched filtering waveform, as " small form " in square frame in Fig. Template can obtain by training in advance, desirable a plurality of when noise is large mean value. As seen from Figure 11, at error sign ratio, be 10 -5 the time the present embodiment demodulation performance exceed " contrast scheme " about 7dB, advantage is very obvious.

Above-described embodiment shows, native system is in the situation that the existing broadcast transmitter of compatibility, completed the in-band on-channel transmission of the high code check digital signal of a road simulated audio signal and a road simultaneously, and receiver all has normal demodulation performance to both, be expected to form the agent technology framework of following China digital am broadcast standard.

The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, for a person skilled in the art, the present invention can have various modifications and variations.

Within the spirit and principles in the present invention all, any modification of doing, be equal to replacement, improvement etc. Although there are a number of ways in which a radio signal may be modulated, one of the easiest is to change its amplitude in line with variations of the sound.

In this way the amplitude of the radio frequency signal varies in line with the instantaneous value of the intensity of the modulation. This means that the radio frequency signal has a representation of the sound wave superimposed in it. In view of the way the basic signal "carries" the sound or modulation, the radio frequency signal is often termed the "carrier".

From the diagram, it can be seen that the envelope of the signal follows the contours of the modulating signal. Amplitude modulation, AM, is one of the most straightforward ways of modulating a radio signal or carrier.

It can be achieved in a number of ways, but the simplest uses a single diode rectifier circuit. Other methods of demodulating an AM signal use synchronous techniques and provide much lower levels of distortion and improved reception where selective fading is present. One of the main reasons for the popularity of amplitude modulation has been the simplicity of the demodulation. It enables costs to be kept low - a significant advantage in producing vast quantities of very low cost AM radios.

As with any technology there are advantages and disadvantages to be considered. The summary below gives a highlight of the basic pro's and con's. Although in the current technological climate, AM in its basic form is not nearly as effective as other modes that can be used, it is still retained in many areas like broadcasting, because of the number of users. However, it is likely that with time, its use will decrease still further and ultimately many AM transmissions will cease.

However, its derivatives like quadrature amplitude modulation are widely used as they offer a very effective form of modulation, espceially for data transmission. Although the use of amplitude modulation is decreasing, it nevertheless forms the basis of other forms of modulation that are still being widely used, or their use is increasing.

AM has advantages of simplicity, but it is not the most efficient mode to use, both in terms of the amount of space or spectrum it takes up, and the way in which it uses the power that is transmitted. This is the reason why it is not widely used these days both for broadcasting and for two way radio communication.

Even the long, medium and short wave broadcasts will ultimately change because of the fact that amplitude modulation, AM, is subject to much higher levels of noise than are other modes. IEEE vol , no. Michael Noll Principles of modern communications technology. Artech House. May Analog television broadcasting topics. Dot crawl Ghosting Hanover bars Sparklies. Sahrawi Arab Democratic Republic Somaliland. Analog and digital audio broadcasting. Radio modulation. C band Ku band L band S band.

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