SSB transmitter for 2 meters. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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As a rule, the most distant communications on the two-meter range can be carried out by telegraph. However, the ability of many ultrashortwaves to conduct long-distance communications is limited by ignorance of the telegraph. The way out of this situation can be the use of single-sideband modulation, which is close to CW in terms of energy and has a significant gain compared to AM. This prompted the author to take up the manufacture of a 144 MHz SSB transmitter.

The transmitter diagram is shown in the figure. A single-sideband signal is formed by the filter method and transferred to the frequency of the two-meter range by successive transformations. The signal from the microphone is amplified by a microphone amplifier (transistors T1, T2).

Transmitter diagram (click to enlarge)

The capacitances of the transition and shunt capacitors are selected so that the frequency response of the amplifier smoothly increases to frequencies of 2-2,5 kHz and then drops steeply. This type of frequency response provides better understanding of the signal when received at the noise level and minimal distortion when limited - the microphone amplifier uses signal limitation by diodes D1, D2, which, in the case of reception at the noise level, is equivalent to an increase in the average transmitter power. The limiter can be turned off by toggle switch B1.

For the convenience of setting up the transmitter, a sinusoidal signal with a frequency of 1 kHz can be fed to the input of the LF amplifier from the generator on the T3 transistor. In the feedback circuit of this generator, a limiter R12, D9 is installed, due to which the transistor does not enter the saturation region and operates in a linear mode, which ensures low distortion of the sinusoidal voltage at a low quality factor of the generator circuit (primary winding of the transformer Tp1 - capacitor C16).

The low-frequency signal from the secondary winding of the transformer Tr2 is fed to the diodes D3 - D6 of the balanced modulator. They are also supplied with voltage from a reference quartz oscillator (T4) with a frequency of 1730 kHz. The quartz filter (Pe2 - Pe5) highlights the upper side band. The received signal through the amplifier (T5) is fed to the diode mixer (D7, D8), where it is mixed with the signal of the second quartz oscillator (T6), which has a frequency of 10 MHz. The total frequency voltage of 11,73 MHz is allocated by the L8C12 circuit and, after amplification in a cascade on the transistor T7, is fed to the control grid of the L2 lamp, which acts as a second mixer. The third grid of this lamp receives a signal with a frequency of 132,5 MHz from a frequency multiplier assembled on the L1 lamp. The anode circuit of the mixer is loaded on a three-circuit filter. The L15 C32, L17C37 circuits are tuned to a total frequency of 144,23 MHz, and the L16C35 circuit is a rejector for the frequency of the third local oscillator.

A power amplifier is assembled on the L3 lamp operating in AB mode. The peak power of the transmitter is 2,5 watts into a 75 ohm load.

Details and construction

The data of coils and chokes are given in the table. Coils L1 - L12 and inductor Dr1 are wound on frames with a diameter of 8 mm, inductor Dr2 - on a frame with a diameter of 6 mm. The rest of the coils are frameless. The inner diameter of the coils L13 - L17 is 7 mm, L18 - 10 mm. The Tp1 transformer is wound on a K20X12X5 toroidal core made of 2000NN ferrite. The primary winding contains 500, the secondary - 200 turns. The Tr2 transformer uses an OL 12 / 20-6,5 core made of E-340 steel, the primary winding consists of 600, the secondary - of 800 turns (with a tap from the middle). For all windings of both transformers, wire PEV-1 0,12 is used. Trimmer capacitors, with the exception of C40, KPM, C40 - an air-ceramic tubular capacitor from broadcast receivers. Its initial capacitance was reduced to 0,7 pF by filing off a part of the silver layer with an abrasive bar.

Permanent capacitors KM or KLS. The quartz resonators of the filter and the reference oscillator (Pa1 - Pe5) were selected according to the method described in the article "Crystal filter for SSB" ("Radio", 1966, No. 7, p. 19). The frequencies of the quartz resonators used in the generators (Pe6, Pe7) may differ from those indicated (provided that there are no combination frequencies lying near the main signal band). It is only necessary that their sum correspond to the two-meter range, and the frequency of the Pe6 resonator should not be lower than 8-10 MHz (otherwise it is difficult to filter the high-frequency generator signal).

The transmitter is made in the form of two blocks - transistor and tube. The transistor block is assembled on a printed circuit board. For better suppression of the SSB carrier signal, the elements of the 1730 kHz generator and the balanced mixer are covered with thin brass screens. The lamp block is made on a box-shaped chassis made of brass with a thickness of 0,5 mm. Such a chassis makes it possible to make the "earth" leads of the parts minimal in length by soldering them directly to the chassis. This eliminates the risk of self-excitation.

For the same purpose, the chassis is divided into compartments by partitions. The baffles extend over the lamp panels in such a way that they separate the anode and grid circuits of the lamps. The signal from the transistor block is connected to the lamp block by a coaxial cable 200 mm long. The length of the cable can be increased, while it is necessary to reduce the capacitance of the capacitor C 29.

The resistances of the base resistors indicated in the diagram are calculated for transistors with a coefficient Bst = 40-60. For other resistance coefficients, they must be proportionally changed. The crystal filter before installation in the transmitter must be adjusted according to the method given in the mentioned article "Crystal filter for SSB".

Setting up the transmitter start with the lamp block. By selecting resistors R26 and R31, the anode current of lamps L2 is set within 20-25 and L3 - 12-16 mA. A resistor with a resistance of 75 ohms and a power of 2 W is connected to the output of the transmitter. Using a wavemeter, tune the L13C23 circuit to a frequency of 66,25 MHz. In the same way, the L14C27 circuit is tuned to a frequency of 132,5 MHz. To improve the accuracy of tuning, the connection of the wavemeter with the contours should be minimal.

Next, a lamp voltmeter is turned on in parallel with the load resistor, a standard signal generator is connected to the control grid L3 (its frequency should be equal to 144,23 MHz), the lamp L1 is removed from the socket and the output circuit is adjusted with capacitor C40 to the maximum voltmeter readings. By connecting the GSS through a small capacitor to the third grid of the L2 lamp, by rotating the rotors of the capacitors C32, C37, the maximum voltmeter readings are achieved. By setting the GSS frequency to 132,5 MHz, the L16C35 circuit is tuned to the minimum voltmeter reading. After that, the L15C32 and L17C37 circuits are again tuned to a frequency of 144,23 MHz. This adjustment stage is carried out with the transistor unit turned off.

Put the lamp L1 in place and turn on the power of the transistor unit. Quartz oscillators on transistors T4 and T6 are tuned using cores to the maximum voltage at the taps of the coils L10, L12.

They rebuild the GSS at 11,73 MHz, connect it through a capacitor to the base of the T7 transistor and achieve resonance in the L9C14C29 circuit, focusing on the maximum voltmeter reading at the transmitter output. After that, a GSS signal with a frequency of 1730 kHz is applied to the base of the transistor T5 and the L5C11 and L8C12 circuits are tuned. The L3C8C9 circuit is tuned with the 1 kHz generator turned on. In all cases, the GSS output voltage is maintained at a level at which the voltage at the transmitter load does not exceed 5-6 V.

If an amateur has an SSB transmitter for 20,14, 10 or 2 meters, then there is no need for a transistor unit. In this case, the signal from the HF transmitter is fed to the grid of the L1,5 lamp. Its amplitude should not exceed 7 V. The frequency of the PeXNUMX quartz resonator in this case must be changed so that the total frequency of the KB transmitter and the selected quartz harmonic corresponds to the frequency of the two-meter range.

The described transmitter operates on a fixed frequency. In competition conditions, there is a need for a smooth change in frequency, at least in part of the range. This can be done if the third local oscillator is made according to the tunable quartz circuit.

The transmitter showed good results in field and stationary conditions.

Author: V. Vylegzhanin (RA3DCN), Istra, Moscow Region; Publication: N. Bolshakov, rf.atnn.ru

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