How does a radio work?

Principle: it is the antenna received from the high-frequency signal by the detector (demodulation) reduced to audio signals, sent to headphones or speakers into the sound wave.

The high-frequency radio signal from the receiving antenna is generally very weak, and it is not appropriate to send it directly to the detector. It is best to insert a high-frequency amplifier between the selector circuit and the detector to amplify the high-frequency signal.

Even if a high-frequency amplifier has been added, the power of the detector output is usually only a few milliwatts, which is fine for headphones, but too small for speakers, so an audio amplifier is added after the detector output to drive the speakers. High-amplifier radios are more sensitive and powerful than direct-detector radios, but they are still less selective and more complex to tune.

The high-frequency signals received from the antenna to amplify hundreds or even tens of thousands of times, there are generally several levels of high-frequency amplification, each level of the circuit has a resonance circuit, when the frequency of the received change, resonance circuits have to be re-adjusted, and each time after the adjustment of the selectivity and the passband is difficult to ensure that it is the exact same, in order to overcome these shortcomings, almost all of the current radios are using super-aberrant circuit.

Expanded Information:

. p>The carrier frequency of the selected high-frequency signal is changed to a lower, fixed, unchanging IF (465 KHz), which is then amplified using an IF amplifier to satisfy the requirements of the detector before it is detected. In the super-aberration receiver, in order to produce the effect of frequency conversion, but also an additional sinusoidal signal, this signal is usually called the aberration signal, the aberration signal circuit, customarily called the local oscillation.

In the radio local oscillation frequency and the frequency of the received signal difference of an intermediate frequency, so in the mixer before the selection circuit, and the local oscillation using a unified tuning line, such as the use of coaxial duplex capacitor (PVC) tuning, so that the difference to maintain a fixed value of the intermediate frequency.

Because the intermediate frequency is fixed, and the frequency is lower than the high-frequency signal has been tuned, the gain of the amplifier can be made larger, the work is also more stable, the passband characteristics can be made more ideal, so that the detector can get a large enough signal, so that the whole machine output audio signals of better sound quality.

The high-frequency signal received by the antenna through the input circuit and the radio's local oscillation frequency (whose frequency is higher than the external high-frequency signal of a fixed intermediate frequency, China's intermediate frequency standard is 465KHZ) together with the frequency converter tube into the mixing frequency converter in the frequency converter stage of the load circuit (frequency selection) to produce a new frequency that is generated through the differential frequency of intermediate frequency.

Intermediate frequency only changes the frequency of the carrier, the original audio envelope does not change, the intermediate frequency signal can be better amplified, the intermediate frequency signal by the detector and filter out high-frequency signals. Then by the low amplifier, power amplification, push the speaker to sound.

Baidu Encyclopedia - Radio