The process of creating a radio is to build a radio transmitter or a device that simultaneously combines the functions of a radio transmitter and a radio receiver. A radio transmitter is a mandatory part of any such device. The presence of the receiver depends on the tasks to be solved.
Before you make your own radio, you need to make sure that the current legislation will not be violated. Broadcasting requires a special license. In its absence, it is allowed to broadcast only within license-free bands or at low power in the FM band.
General information about radio transmitters
Each radio transmitter has two main parameters by which it can be classified into one category or another: transmission power and frequency range. Power is measured in Watts. Range - these are the extreme values \u200b\u200bof the oscillation frequency of radio waves in which the transmitter is capable of operating. Usually it is indicated on the regulator scale in the form of digital divisions. On older models, instead of numbers for the range (for example, 107.7 FM), the wavelength was indicated. Wavelength is directly related to frequency.
There is also a third device parameter - modulation. Any radio wave can be given amplitude, frequency or phase modulation. There are also more complex types, for example, SSB or phase with simultaneous amplitude modulation.
For what purposes can radio be used
Before you make a homemade radio, you need to decide for what purposes it will be used. It can be a broadcast transmitter (a home analogue of a broadcast station), or a device for maintaining radio communication between several devices.
All homemade radios are divided into two groups: broadcast and communication transmitters (the receiver can also be connected). Receivers collect those who wish to receive information from the air from open service communication channels.
Receiver for transmitter setup
The most important tuning device is the receiver. This product can be purchased from a specialized store (unless the radio transmitter to be assembled does not fall within the standard range). Therefore, before you make your own radio, you need to buy a device to work in the right range.
If we are talking about broadcast transmitters, then it is better to start practicing with equipment operating in the medium wave range. Such devices were installed on old receivers, and are currently being installed on modern Chinese radios. They have two benefits:
- make transmitter easier;
- it will not interfere with other appliances.
Ba small number of broadcast radio stations operate on the medium wave band (with the exception of large cities).
But there is also a drawback - poor sound quality. With careful tuning, the radio will be suitable for speech transmission, but not for music broadcasts.
Selecting the source of vibrations (radio waves)
In order to make a simple radio, you need a source of oscillation, radio waves. It is called a "reference oscillator", "master oscillator", or "frequency synthesizer".
There are several options for its manufacture:
- Purchase of quartz (a metal crystal with two leads) and its soldering into the circuit. The option is simple and convenient. The main parameter for selection is the frequency of quartz, 27.777 MHz is suitable.
- Purchasing a crystal oscillator (same as regular quartz, but has four pins).
- Assembling a parametric generator (coil winding). Used by beginners, but when working on the FM band, such a device is not reliable.
- Building a lamp generator. A popular option in the past, but now rarely used. Working with lamps is not recommended for beginners, as it involves the use of high voltage. Using lamps, you can assemble a very powerful transmitter.
- Purchasing a ready-made frequency synthesizer. The easiest, but also the most expensive option.
- Purchasing or using an existing device (such as a Chinese FM transmitter). This option is recommended for beginners.
The selected oscillation source must be connected to an amplifier and an antenna that can bedo it yourself. It is advisable to install a filter (P-loop) between the amplifier and the antenna.
Selecting the transmitter scheme
The main rule for beginners is to take only ready-made and proven schemes. They are posted by radio amateurs on the Internet, commented on thematic forums. Can be viewed in Radio magazine.
To decide how to make your own radio at home, you need to choose a radio microphone circuit. The best solution would be to use a classic wireless microphone, which can be assembled in your own case or from similar devices.
Radio microphones or "bugs" are the best option for your radio. These devices are analogues of mass-produced FM-transmitters. The main difficulty is to ensure the miniaturization of the product. A common mistake is to try to "squeeze" the radio microphone to the size of a coin. They often do not work on this scale, so the board must be made in standard sizes.
Manufacture of radio headphones
In radio headphones, the transmitter is located on the sound source, and the receiver is located directly in the headphone case. Before making radio headphones, you need to assemble both devices, but on the condition that the receiver is made from a finished module.
A module is a chip with a board (constructor kit) that needs to be built into the headphones, connected to a button and a battery. The following miniature FM headphone receiver modules are popular:
- AR1310 - has a size smaller than a ruble coin and a 32 ohm headphone output (the mostcommon model).
- AR1010 is a two-pea-sized push-button module that does not require a second chip.
- TEA5767 is the smallest built-in headphone module.
- RDA5807 - Chinese FM module without digital control.
- Si4703 is a handy module with a larger connector.
It is better to choose options that do not require digital control. They are easier to work with than a wireless headphone receiver.
The transmitter for wireless headphones is best done on your own. You can consider purchasing a ready-made module, but then valuable experience will not be gained on how to make a radio at home. Self-assembly is recommended, as it will be cheaper. Transmitters are much simpler than receivers and are easier to assemble and set up.
DIY radio transmitter assembly
Assembly is recommended to be carried out in the classical way - to use a printed circuit board to which to solder the components of the circuit. After that, set everything up with the help of special devices and place it in the case.
Do-it-yourself PCB manufacturing requires chemicals and a bath. It is undesirable to use ferric chloride because of its soiling. Instead, hydrogen peroxide and citric acid are used. Hydrogen peroxide is better to buy concentrated for the pool or perhydrol.
The pattern on the board can be drawn with a marker or printed on a printer. To giveradio appearance of a professional device can use photoresistor.
It is recommended to use a ready-made board drawing for the selected scheme. For self-development, you can use specialized programs.
Soldering, radio transmitter assembly
When soldering the device, do not allow the components to overheat. This is especially critical for transistors and microcircuits, which cannot be soldered for more than 2-3 seconds.
A soldered electronic device needs tuning. It is forbidden to connect power to powerful transmitters before they are cascaded.
Setting up a homemade radio
Setting is the final and most difficult stage of production. Before you make a radio yourself, you need to purchase special devices to adjust it: a tester and a receiver. An example setup algorithm is as follows:
- First, the tester checks all electrical soldering connections, current consumption, voltage drop in circuit sections. The operation of each transmitter stage is checked.
- A wavemeter is made to the tester in voltmeter mode. The probes are connected to the same coil that is installed in the transmitter. When the power is connected, the arrow should show voltage pickups through the air. Between the wavemeter coil and the tester, you must install a microwave diode, which is sold in shops for radio amateurs.
- The receiver is tuned to the frequency of the radio transmitter. After receiving a broadcast signal, the frequency and power are adjusted. Cancheck "communication range".
To improve the quality of tuning receivers and transmitters, you can use the following devices: frequency counter, microwave oscilloscope, wavemeter, power meter, wattmeter. If the interest in how to make your own radio develops into a professional hobby, you can gradually increase the complexity of the assembled devices.
