Radio transistors with their hands

Yunostru on YouTube user posted a series of videos, with which it is appropriate to begin to learn how to make a radio transistors themselves. Discuss curious rollers start with theory, shows which stages are in the device what the purpose parts. On the screen the modulation missed questions. You can not do without knowing the meaning, when it comes to radio transistors. Forget FM, if not around the frequency demodulation chips! In the video, radio transistors for HF bands and CB are not any programs to catch out. Find out ahead of time that is required to collect radio transistors own.

Transistor radio

Structural scheme

A typical receiver includes:

  1. Antenna.
  2. The input stage of customizable filters.
  3. a high frequency amplifier.
  4. Oscillator to the transducer.
  5. Intermediate frequency amplifier.
  6. Detector.
  7. Low-frequency amplifier.
  8. Speaker.

Construction covered by feedback frequency control and gain control.

radio design

The transistor radio device includes:

  1. The antenna converts the ethereal waves into electricity. Without it, some receivers work, but the quality drops sharply, in remote areas is no reception. Note waves differ in frequency and polarization. Depending on the performance of the antenna structure is changing. The broadcasting adopted linear vertical polarization, in the simplest case, the waves are caught on the pin a quarter of the period length. For example, for a frequency of 100 MHz: ¾ meter. Not every person has the opportunity to wear such a piece of wire in a vertical position, therefore, used ferrite, framework and other types of antennas, takes up little space. So, first of all the specified item is selected, without antenna radio transistors, collected his own, will not pull any program.
  2. The antenna converts the ethereal waves into electricity. Here there is a primary selection. Ether filled cloud waves from kilometer to submillimeter length. Emit tower communication, sun, moon, galaxies, planets, space directly. Obviously, the radio transistors does not require the information described in a heap. Antenna primary filters the signal. More coming waves, where the reception of the length of a quarter-wave, half, etc. Still get a large amount, unnecessary to the user. Most pins have no direction in space in azimuth, it is difficult to isolate a single tower of others. Needed resonant circuit. This radio cell transistors composed of the capacitor and the inductor. Already discussed selective properties, adding that the fine adjustment is carried out within the range of capacitors, switches between MW, LW, HF, VHF, going rough, irregular. For this purpose, a plurality of resonant circuits within, one for the range. Cascade transistors
  3. When the desired signal is selected, it is necessary to be strengthened. Amplifier stage transistors, made by any scheme. If the construct for a single radio channel, a copy of the textbook circuit for frequency. The last parameter depends on the type of transistor (divided by the boundary frequency), the rest of the circuit is similar as two drops of water. There comes an important point, it's time readers know that the signal is encoded in two ways: frequency and amplitude modulation. Dubbed oversimplification, but the battle for the FM radio frequencies in our opinion unlikely to be able to collect ordinary citizen. The sound is encoded in stereo, which requires additional circuitry, not talking about the automatic frequency control. We would like to say - easier to make radio transistors for HF, CB band where the amplitude modulation is applied. It calculated the design of video uploaded on YouTube. Do not attempt to collect similar to FM.
  4. Acceptable signal amplification is difficult to provide with high selectivity at the transmission frequency. This applies to radios with transistors that require a large dynamic range to provide. In the case of a single station requirements of virtually leveled, the cascade of inverter may throw. It transfers the useful signal at 465 kHz for amplitude modulation or the frequency for the unit of MHz. Easier to understand the musicians. Anyone know what it means to transpose. If the song is too high tonality soloist may not execute chords smoothly transferred down to the desired number of notes. The frequency converter does analogy - special built-LO generator generating oscillations by exactly the value of the intermediate frequency above the carrier. If the broadcast proceeded to 10 MHz is obtained for the amplitude modulation 10.465 MHz. The frequency converter is an amplifier stage operating in the linear mode, where the base comes the received signal, and an emitter - LO signal. The result is the subtraction that gives the desired effect. The design of the radio
  5. Finally, we reached the detector. This stage is where the information is removed from the carrier the user to hear. In the case of amplitude modulation in the simplest case, a semiconductor diode, is obtained half-wave rectifier. Readers have already realized that there are more complex structures resembling bridges, known to fans of Switching Power Supplies. In this case, more power is given to the load. Not to mention about the frequency detectors, consider for readers' comments.
  6. The rectified signal picked up from the detector is amplified low frequency stage (to 15 kHz) and fed to headphones or loudspeaker. amplifier design does not differ from the preliminary, the power is much higher, so the transistors are on metal radiators of considerable size. In modern radios electronic components on chips. However, the low-frequency amplifier is still easy to find, looking for a massive heatsink. Looks funny: all radio is assembled on a single tiny chip and conclusions go on a huge low-frequency amplifier, fitted to a metal structure respectable size.

The choice of the working point of the transistor

Omitted references to automatic frequency control, gain control. At home, the circuit can be realized by having at hand a textbook or a special program. Now Yandex check for aids for the design of radios. Note that the textbooks of Soviet times to allow institutions to make their own radio transistors, since the antenna and ending with frilly cascades, and is written quite clearly.

Choosing a working transistor radio for point

It is time readers know that digital technology is built on a transistor operating in cutoff mode. This means that the pulses are either not tested, obtained ones and zeros. Even passive resistance in the processor No, it's just a pile of transistors and field. So, the choice of the operating point.

Transistor two main characteristics:

  • entrance;
  • output.

In the input voltage delayed horizontal, vertical current. At the first step is calculated the input signal voltage supplied to the base. Variable, so it operates on a large scale. It is necessary to find the minimum and maximum current. Then he made a clever move: it is considered that the electrons leave the collector. This slightly unfair: guest current transmission rate at rough calculations for selecting the operating point.

The output current characteristic is dependent on the voltage. Wherein the family of characteristics is obtained, depending on the base current. It varies (already found above the minimum and maximum value), and the operating point wherein a line running through:

  1. It begins on the horizontal axis. Attention! Selection of the source voltage. The line starts at the cell voltages batteries.
  2. The vertical axis of the current limiting resistor in the collector circuit (between the collector and the battery). Choose Ohms, adjustable slope. The maximum current flow should not burn transistor (look limiting characteristics of the directory).

the maximum base current family does not exceed the working line.

Later, we describe how to make an antenna for the radio.

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