A simple SSB mini transceiver for 160 meters. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Direct conversion technology quickly gained popularity among radio amateurs due to the combination of high technical parameters with the utmost simplicity of circuit solutions. However, the known designs are quite difficult to manufacture.

A simple transceiver with fairly good parameters is proposed, containing a minimum of details. The design uses separate circuit solutions of the RA3AAE transceiver [1]. Its sensitivity is at least 5 μV; the power supplied to the terminal stage at a supply voltage of 12 V is 400 ... 500 mW. With an increase in the supply voltage of the terminal stage to 24 V, the power increases to several watts, but at the same time it is necessary to put a KT606 transistor in the terminal stage, and KT907 in the final stage.

The circuit diagram of the transceiver is shown in the figure. It uses a reversible SSB modulator-demodulator.

(click to enlarge)

ON RECEPTION (RX) the signal from the antenna through the normally closed contacts of the relays K1 and K2 and the capacitor C14 is fed to the radio frequency input of the SSB modulator-demodulator. The mixer also receives the voltage of the local oscillator, made on the transistor VT5 according to the scheme with capacitive feedback. The local oscillator operates at the frequency of the received signal, both when receiving and when transmitting. Next, the low-frequency signal is fed to the input of the universal ULF, which operates both during reception and transmission and is made on transistors VT6, VT7 with direct connection. Diode VD 10 is used to connect a microphone to the universal ULF input in transmission mode.

ON TRANSMISSION (TX) the supply voltage is applied to the relays K1, K2, the preamplifier (made on transistors VT1 and VT2) and the final stage on transistors VT3 and VT4. At the output of the final stage, a U-shaped low-pass filter (LPF) is installed, which, during transmission, is connected to a matched antenna by the contacts of relay K2.

SETTING UP THE TRANSCEIVER start in receive mode. First, the sliders of all tuning resistors (R10-R12, R16) are set to the middle position. Then, rotating the tuning core of the coil L13 and selecting the capacitance of the capacitor C27, we obtain an overlap in the local oscillator frequency of 1830 ... 1930 kHz.

On the collector of the transistor VT7 there should be 0,5 Upit., Which is achieved by selecting the resistance of the resistor R21. Then, in the evening or at night, when a large number of radio stations are operating, we connect the antenna and, rebuilding the local oscillator with capacitor C26 (tuning), we try to receive one of the powerful stations. If this fails, we rotate the trimmer resistor R16, setting the value of the high-frequency voltage necessary for optimal operation of the mixer. This achieves the maximum volume of the received station in the phones. Next, we rotate the tuning core of the L6 L7 coil, achieving maximum volume when receiving weak signals. On this, the transceiver setup in the receive mode can be considered complete. We connect the equivalent of the antenna to the output of the transmitter (a 75 Ohm resistor with a power of at least 2 W) and measure the high-frequency voltage across this resistor. In this case, it is necessary to apply a signal to the microphone input of the universal ULF from a low-frequency generator or microphone.

You can also unbalance the mixer by setting the slider of the resistor R11 or R12 to one of the extreme positions. By adjusting the circuits LI C4 and L3 C8, we achieve the maximum voltage on the equivalent. If self-excitation occurs, chokes L2 and / or L4 should be shunted with resistors of small ratings (selected experimentally). Next, we balance the mixer using resistors R11 and R12, achieving the absence of a carrier at the output of the transceiver in the transmission mode. In this case, there should be no signal at the microphone input of the universal ULF. Having received the maximum carrier suppression in the transmit mode, we again switch the transceiver to receive and, listening to the signal of the GSS or another analogous local oscillator used in the transceiver, we achieve maximum suppression of the upper sideband (VBF) using the tuning resistor R10. The easiest way to do this is when listening to an unmodulated carrier by detuning the local oscillator of the transceiver down in frequency by 1...1,5 kHz relative to the frequency of this carrier [1].

Sometimes, for better suppression, you have to select the capacitance of the capacitor C17 of the high-frequency phase shifter within 240 ... 390 pF or select the resistance of one of the resistors of the low-frequency phase shifter (R13 or R14), and then repeat the adjustment again. A mixer adjusted at reception will also suppress the EBP at transmission. Any RF germanium or silicon diodes can be used in a single-way mixer. The following types of diodes give the best results: KD514, KD503, D311, GD507. Capacitances of separating and blocking capacitors are not critical. An air dielectric capacitor is used to tune the local oscillator. Relays K1, K2 are small-sized, with a response voltage of 9 ... 12 V. The winding data of the coils are given in the table.

Notes:
1. Coils L6 and L7.L12 and L13 - on the same frame.
2. As coils L2, L4, L8 and L9, ready-made chokes of industrial production were used.

All parts of the transceiver are mounted on five printed circuit boards with a maximum "ground" area.

Literature

1. Polyakov V.T. Radio amateurs about the direct conversion technique. - M., Patriot, 1990, 24s.
2. Komarov S. Simple single-band telegraph transmitter. - Radio, 1982, No. 7, pp. 25-26. Radio amateur 1/94 p.45-46.

Author: V. Artemenko, Kyiv; Publication: N. Bolshakov, rf.atnn.ru

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