Dual band antenna amplifier. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Dual band antenna amplifier. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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In the VHF bands (144 and 430 MHz), to work with dual-band radio stations, radio amateurs often use dual-band antennas with vertical polarization ("cactus" or industrial production: Diamond, Sirio, Anli, etc.), powered by one cable. To improve reception in the VHF bands, antennas are equipped with antenna amplifiers, so in this case a dual-band amplifier is needed. It is not advisable to use a broadband amplifier, for example, from television antennas, since this can lead to crosstalk distortion. Much better results can be obtained if selective amplifiers are used, for example, such as in [1,3]. If they are combined into a common design, you get a dual-band antenna selective amplifier.

The device consists of two nodes: the amplifier itself and the power supply module. The amplifier circuit is shown in fig. 3. On transistors VT1 and VT2, amplifiers are assembled for the ranges of 430 and 144 MHz, respectively. The supply voltage is stabilized by the DA1 stabilizer. Diodes VD9 and VD10 reduce the voltage to 3,5 V, which is recommended for the transistors used. If other transistors are used, these diodes can be omitted.

(click to enlarge)

If the supply voltage is not supplied to the amplifier, the signal from the antenna through the contacts of the relay K1.1, the capacitor C1 and the contacts K2.1 goes to the output socket XW2. When power is applied (through the drop cable), the relays will operate and connect the input and output jacks to the amplifiers.

The input signal of the 144 MHz range through the L2C4L3 low-pass filter goes to the input circuit L4C6 of one amplifier, and the signal of the 430 MHz range through the high-pass filter C2L1C3 goes to the input circuit L5C5 of the second amplifier. Diodes VD1 - VD8 protect transistors from transmitter signals. After amplification, the signals are fed to the adder, assembled on the transformer T1, and then to the output. The layout, assembled according to this scheme, provided a gain of 12 ... 14 dB in the 144 MHz range and 9 ... 10 dB in the 430 MHz range. To obtain greater gain, transistors with a greater steepness must be used.

Coils L1, L2, L3, L6, L7 are wound with PEV-2 0,4 wire on a mandrel with a diameter of 4 mm and contain 2, 3, 3, 7 and 12 turns, respectively. L4 and L8 are wound with PEV-2 0,9 wire on a mandrel with a diameter of 4 mm and contain 5 (retraction from the first turn) and 7 turns, respectively.

Choke L10 - DM-0,2 with inductance 10...40 μH. Transformer T1 is wound on a ferrite ring with an outer diameter of 5 mm. The winding is carried out with a double-folded wire PEV-2 0,2, the number of turns is 10. Relays K1 and K2 are REK-43 with a response voltage of 5,5 ... 6 V.

The voltage to the antenna amplifier is supplied via the drop cable through the power module (Fig. 4). It provides a supply voltage of 7 ... 8 V in the receive mode and automatically turns off the amplifier in the transmit mode. The module is connected between the transceiver input and the drop cable. It contains a voltage regulator on a transistor VT1, a rectifier on diodes VD1, VD2 and a key on a transistor VT2.

In the initial state (shown in the diagram), the SA1 toggle switch is open, so the antenna amplifier is de-energized and the signals go bypassing the amplifying stages. When the SA1 toggle switch is closed, a voltage of 6,5 ... 7 V is supplied to the amplifier, and its relays are triggered. When the transceiver switches to transmission mode, its signal is rectified and fed to the base of the transistor VT2. It opens, the voltage at the base of the transistor VT1 decreases to almost zero and the amplifier power is turned off - the transceiver output will be connected directly to the antenna, bypassing the amplifier stages.

At the end of the transmission, the transistor VT2 will close and the power will again be supplied to the antenna amplifier.

The power supply module is connected to a stabilized power supply with a voltage of 12 ... 15 V, for example, to the same one that powers the transceiver itself.

PCB drawings

Literature

Nechaev I. Antenna amplifier of the range of 2 meters. - Radio, 2000, No. 1, p. 62, 63.
Nechaev I., Lukyanchikov N. UHF in the Mayak radio station. - Radio, 2000, No. 9, p. 63,64.
Nechaev I. Two designs for a VHF radio station. - Radio. 2000, no. 11, p. 62,63.

Author: I. Nechaev (UA3WIA), Kursk

See other articles Section Civil radio communications.

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