420 MHz transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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Ivanovo ultrashortwave developed a simple transmitter for the 420 MHz band. His work was tested during the Field Days of 1958 and 1959. The transmitter provided reliable communication at a distance of 30 km. It is very simple in design and does not contain scarce parts.
As can be seen from the circuit diagram (Fig. 1), the generator is assembled according to a push-pull circuit with self-excitation on two lamps of the 12C3S type (L1 and L2). Instead of this lamp, you can use 6N15P and GI7B, but this option is very uneconomical, and efficiency is especially important in working conditions during the "field day".
Ris.1
The power given by the transmitter to the antenna is 1,0-1,5 watts. A two-wire line with a jumper is used as the L1 circuit. Communication with the antenna is inductive, carried out using a loop of communication L1. Setting the generator circuit to the required frequency of the amateur band is carried out using a short-circuit jumper. Inductors Dr1, Dr2, Dr3 and Dr4 in the filament circuit and Dr5, Dr6 in the cathode circuit are used for high frequency decoupling. The resistance R1 is the leakage resistance, in addition, the bias voltage is removed from it. The mode of operation of the generator and the output power depend on the value of this resistance.
The transmitter uses anode modulation. The modulator is a conventional low-frequency amplifier on a 6P15P (L3) lamp, which has a large steepness. The microphone is carbon, powered by voltage in the automatic bias circuit of the L3 lamp.
Construction and details
The L1 line is made of thin-walled copper tubes with a diameter of 6 mm, and the connection coil with the antenna is made of bare copper wire with a diameter of 4 mm. Their dimensions are shown in Fig. 2 a, b. The distance between the connection coil and the two-wire line is 9 mm.
Ris.2
Lamps L1 and L2 are mounted upside down. The sockets of the lamp panel are soldered to the line tubes, connected to the anodes L1 and L2. The transmitter is made in the form of two separate blocks: generator and modulator. This allows you to mount the generator directly on the mast along with the antenna, and the modulator is located at the operator. Fig.3 gives a visual representation of the location of all the details.
Ris.3
RF inductors (Dr1-Dr8) are wound on a blank with a diameter of 6 mm and contain 7 turns of silver-plated wire with a diameter of 1 mm. As a modulation choke Dr9, any output transformer is used (for example, from the receiver "Baltika", "Ural", etc.). Instead of the microphone transformer Tp1 with a transformation ratio of 1:30, you can use the output transformer from the broadcast receiver.
The generator is mounted on an 85x250 mm plate made of organic glass 5 mm thick. It is connected to the modulator with a three-wire cable.
The transmitter is designed to operate at a fixed frequency. The frequency can be changed by moving the jumper along the line on which marks are made corresponding to the boundaries of the amateur band.
The manufactured transmitter usually does not require any adjustment and immediately starts working. It is only necessary to choose the value of the resistance R1 according to the maximum power given to the antenna. It should be borne in mind that the anode voltage of the 12C3C lamp should not exceed 120 V, otherwise it will fail.
The transmitter is equipped with a seven-element "Wave channel" antenna. The active vibrator is soldered directly to the ends of the antenna coil. If you want to use the transmitter in stationary conditions, the antenna coil must be connected to the antenna with a RK coaxial cable. In this case, the coaxial cable introduces losses.
To power the anode circuits, a constant voltage of 120-140 V (current consumption 70-80 mA) is required, to power the glow - 12 V (current consumption 0,97 A).
Author: R. Sheshan, (RA3VGR); Publication: N. Bolshakov, rf.atnn.ru
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