Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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In the last year and a half, the interest of radio amateurs in the 1260 MHz band has noticeably increased. The easiest way to master it is converters or transverters to the 144 or 430 MHz band equipment already available to radio amateurs. The converter offered to the attention of readers is designed to convert signals from the 23 cm range into signals from one of these ranges.

When conducting radio communications on the amateur 1260 MHz band or to receive signals from amateur radio IC3, converters are often used that convert signals from this band to signals in the 430 or 144 MHz band.

On fig. 1 shows a 1260/430 MHz converter circuit.

(click to enlarge)

The RF input circuit is formed by a strip line L2 and a capacitor C5. On the transistor VT3 (2T3132A-2), an URF is built, the bandwidth of which is 30 ... 40 MHz, the gain is 9 ... 11 dB, and the strip line L7 and capacitor C16 serve as an element of frequency selection.

The local oscillator operating at the frequency of the odd harmonic of the quartz resonator, determined by the setting of the L1C4 circuit, is assembled on a transistor VT1. The frequency multiplier and amplifier are made on transistors VT2 and VT4, respectively. To isolate the signal of the required harmonic of the generator, they use resonant circuits L4C10 and L8C18, also made on the basis of strip lines. The converter mixer is a double-gate field-effect transistor VT5.

The supply voltage of the mixer is stabilized by the integral stabilizer DA2, and the remaining nodes are powered through the integral stabilizer DA1. Diodes VD1-VD4 are used to protect the device from powerful transmitter signals.

The device works like this. The input signal is fed to the RF amplifier, after which it is fed to the first gate of the VT5 transistor, and the local oscillator signal to the second. The IF signal (430 MHz), obtained as the difference between the frequencies of the RF and local oscillator signals, is selected by the L10C24C25 circuit and through the L11C27L12C30L13 low-pass filter, which has a cutoff frequency of about 460 MHz, is fed to the output of the device.

The overall gain of the converter is +11...14 dB. The device is powered by +12...20 V.

In the absence of some parts, as a replacement in the device, you can use: DA1 microcircuits - KR1157EN801A (B), KR1157EN802A (B), D A 2 - KR1157EN501A (B), KR1157EN502A (B); transistors VT2, VT4 - KT382A, KT3120A, VT3 - KT3101A; quartz resonator ZQ1 - PK212; capacitor C28 - K50, tuned capacitors - KT4-25, pass capacitor - K10-53, KTP, permanent non-polar capacitors K10-17V; tuned resistors - SPZ-19, constant - MLT, R1-4, R1-12.

Coil L1 is wound with PEV-2-0,8 wire on a mandrel with a diameter of 4 mm and contains 4 turns (winding length 7 ... 8 mm) with taps from the 1st and 3rd turns. Coils L10 - L13, containing 3, 1,5, 2,5 and 1,5 turns, respectively, are wound with the same wire on a mandrel with a diameter of 3 mm. Coils L3, L5, L6, L9 are wound with wire PEV-2-0,2 on mandrels with a diameter of 3 mm and contain 8-10 turns. The design of the resonators L2, L4, L7, L8, made in the form of a bracket made of a copper plate (preferably silver-plated) with a thickness of 0,2 ... 0,4 and a width of 5 mm, is shown in Fig. 2.

The installation of most parts is made by surface mounting on a printed circuit board made of double-sided foil fiberglass. On one side of the board (Fig. 3) there is a crystal oscillator, a frequency multiplier and an amplifier, and on the second (Fig. 4) - UHF, a mixer and a low-pass filter.

(click to enlarge)

The board is installed in a metal case (Fig. 5) 25 - 30 mm high and soldered to it along the perimeter from both sides. Coaxial connectors and a pass-through capacitor C31 are installed on the case, the case of which must be soldered to the device case. Installation of parts must be carried out after installing the board. The case is closed with lids on both sides.

The local oscillator of the 1260/430 MHz converter uses a quartz resonator at a frequency of 23,8 ... 24,1 MHz. The generator operates at a frequency of 214 ... 216,9 MHz (9th harmonic of a quartz resonator). The frequency multiplier is tuned to the 4th harmonic of the generator (856 ... 866 MHz) by resonant circuits L4C10 and L8C18. In this case, the converted RF signal can be received in the frequency range 430...440 MHz. When using a broadband receiver, you can use quartz resonators with frequencies other than those indicated.

When using the converter in conjunction with a 144 MHz receiver or transceiver, a 25,6 MHz quartz resonator (9th harmonic) must be used. In this case, the multiplier and amplifier are tuned to the fifth harmonic of the generator (approximately 1150 MHz). Accordingly, it is necessary to proportionally increase the number of turns of the coils L9, L10 and change the parameters of the low-pass filter elements (the capacitance of the capacitors C27, C30 and the inductance of the coils L11-L13 must be tripled).

Setting up the device comes down to tuning the circuits with trimmer capacitors to the appropriate frequencies. With the help of capacitors C3, C4, stable operation of the generator at the frequency of the quartz resonator is achieved. Capacitors C10, C18 and resistor R4 receive the maximum level of the local oscillator signal at the second gate of the transistor VT5 (by the maximum gain of the mixer). Rebuilding the capacitors C5, C16, C24, C25, achieve the maximum transfer coefficient of the converter. Tuning is carried out by ear, using a beacon of the 1260 MHz band as a control signal, or a radio station in this band, taken some distance away to attenuate the signal.

Author: I. Nechaev (UA3WIA), Kursk

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