The intercom is a two-way mobile communication tool that was first produced in the 1920s in Westinghouse's laboratory. What is an intercom? Below is some content I have collected and compiled. I hope it will be helpful to you.
Introduction to walkie-talkie phones
Walkie-talkies can make calls without any network support, and there are no phone charges. They are suitable for situations where calls are relatively fixed and frequent. Due to the rapid technological progress and development in this field, it will not be long before walkie-talkies are as popular as light bulbs and semiconductor radios, making everyone's life easier and more convenient. The history of the development of walkie-talkies
Walkie-talkie technology first emerged in the turbulent twenties, and was born in the Westinghouse laboratory. An eccentric inventor named John Kermode had a whimsical idea of ??automatically sorting postal documents. At that time, every idea about the application of electronic technology was very novel. His idea was to mark envelopes with walkie-talkies, where the message in the walkie-talkies would be the recipient's address, much like today's postal codes. For this reason, Kermode invented the earliest walkie-talkie logo. The design was very simple, that is, one "bar" represents the number "1", two "bars" represent the number "2", and so on. He then invented a walkie-talkie reading device consisting of basic components: a method (capable of emitting light and receiving reflected light) to measure the reflected signal strips and voids, the edge positioning coil; and a method of using the measurement results, the translator coder.
Kermode used the newly invented photovoltaic cells at the time to collect reflected light. What is reflected back from the air is a strong signal, and what is reflected back from the strip is a weak signal. Unlike today's high-speed electronic component applications, Kermode uses magnetic coils to measure bars and spaces. It's like a child connecting a wire to a battery and wrapping it around a nail to clip paper. Kermode uses a coil with an iron core to attract a switch when it receives a signal from the air, and when it receives a signal from the bar, it releases the switch and turns on the circuit. As a result, the earliest walkie-talkie readers were noisy. The switch is controlled by a series of relays, with the on and off states determined by the number of strips printed on the envelope. In this way, intercom symbols sort letters directly.
Shortly thereafter, Kermode collaborator Douglas Young made some improvements based on the Kermode code. The amount of information contained in Kermode codes is quite low, and it is difficult to program more than ten different codes. Young codes use fewer bars, but take advantage of the varying sizes of spaces between bars, much like today's UPC intercom symbols use four different bar and space sizes. The new walkie-talkie symbols can encode a hundred different regions in the same size space, while the Kermode code can only encode ten different regions.
It was not until the patent documents of 1949 that the omnidirectional walkie-talkie symbol invented by Norm Woodland and Bernard Silver was recorded for the first time. There was no record of the walkie-talkie technology in the patent documents before that, and there was no record of the walkie-talkie technology. A precedent for practical application. Norm Woodland and Bemard Silver's idea was to take the vertical bars and spaces of Kermode and YOung and bend them into a ring, much like an archery target. In this way, by scanning the center of the pattern, the intercom symbol can be decoded, regardless of the direction of the intercom symbol.
In the process of continuously improving this patented technology, a science fiction writer Isaac-Azimov described in his book "The Naked Sun" a new method of information encoding. Examples of automatic identification.
At the time, people thought the radio symbol in this book looked like a checkerboard with square tiles, but today's radio professionals will immediately realize that it is a two-dimensional matrix radio symbol. Although this walkie-talkie symbol has no direction, positioning, or timing, it is clear that it represents a high information density digital encoding.
It was not until 1970, when Iterface Mechanisms developed the QR code, that printing and reading equipment for two-dimensional matrix intercoms became available at a price suitable for sale. At that time, two-dimensional matrix intercoms were used to automate the typesetting process in newspapers. The two-dimensional matrix intercom is printed on paper tape and read by today's one-dimensional CCD scanner. The light from the CCD shines on the paper tape, and each photocell is aimed at a different area of ??the paper tape. Each photocell outputs a different pattern depending on whether the intercom is printed on the paper tape, and the combination produces a high-density information pattern. In this way a single character can be printed in the same size space as a single bar in early Kermode codes. Timing information is also included, so the whole process is reasonable. When the first systems hit the market, the complete equipment, including printing and reading equipment, cost approximately $5,000.
Shortly thereafter, with the continuous development of LEDs (light-emitting diodes), microprocessors and laser diodes, there was an explosion of new identification symbols (symbolism) and their applications, which people called ?Walkie-Talkie Industry?. Today it is rare to find a company or individual who has not been directly exposed to fast and accurate walkie-talkie technology. Since the technological progress and development in this field are very rapid, and more and more application fields are being developed every day, it will not be long before walkie-talkies are as popular as light bulbs and semiconductor radios, and will make every one of our lives better. All become easier and more convenient. The working principle of an intercom phone
The transmitting part
The phase-locked loop and the voltage controlled oscillator (VCO) generate the transmitted radio frequency carrier signal, which is buffered and amplified, exciter amplified, and power amplifier. The rated RF power is generated, passes through the antenna low-pass filter, suppresses harmonic components, and then is emitted through the antenna.
Receiving part
The receiving part adopts the double frequency conversion superheterodyne method. The signal input from the antenna undergoes radio frequency amplification after passing through the transceiver conversion circuit and the bandpass filter. After passing through the bandpass Filter, enter a mixing frequency, mix the amplified signal from the radio frequency and the first local oscillator signal from the phase-locked loop frequency synthesizer circuit at the first mixer
and generate the first intermediate frequency Signal. The first IF signal passes through a crystal filter to further eliminate clutter signals in adjacent channels. The filtered first IF signal enters the IF processing chip and is mixed again with the second local oscillator signal to generate a second IF signal. The second IF signal passes through a ceramic filter to filter out unwanted spurious signals, and then is amplified and frequency-identified. Generate audio signals. The audio signal passes through amplification, bandpass filter, de-emphasis and other circuits, enters the volume control circuit and power amplifier for amplification, drives the speaker, and obtains the information required by people.
The signaling processor converts the human voice into audio electrical signals through the microphone. The audio signals enter the voltage-controlled oscillator through the amplifier circuit, pre-emphasis circuit and band-pass filter for direct modulation.
The CTCSS/DTCSS signal generated by the CPU is amplified and adjusted, and then enters the voltage controlled oscillator for modulation. After receiving the low-frequency signal obtained after frequency identification, part of it is filtered and shaped by amplification and sub-audio bandpass filters, enters the CPU, and is compared with the preset value, and the result controls the output of the audio power amplifier and speaker. That is, if it is the same as the preset value, the speaker will be turned on, if it is different, the speaker will be turned off.
Whether it is an intercom application for security inspections or communication during travel, it seems that the performance of intercoms is inseparable. However, why do walkie-talkies communicate wirelessly, and how much do you know about its working principle? Let’s analyze the working principle of walkie-talkies for everyone.