Antenna for portable CB radio station. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / VHF antennas

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The magazine "Radio" has already talked about matching small antennas ("Radio", 1996, No. 4). This article describes a variant of an extended antenna for a portable radio station.

The general view of the antenna is shown in fig. one.

Here 1 - a pin made of elastic steel wire (piano) with a diameter of 2 ... 2.4 mm; 2 - adjustment and coordination device; 3 - pin part of the connector corresponding to the antenna socket of the radio station.

Schematic diagram of the matching device is shown in fig. 2.

P-loop L1C1C2 transforms the active resistance of the antenna system to 50 ohms. and the extension coil L2 lowers the resonant frequency of the antenna system to 27 MHz.

Coil L1 - frameless. It is wound with PEV-2 0,8 wire on a mandrel with a diameter of 6 mm. The number of turns is 9. And the winding length is 12 mm. Coil L2. containing 40 turns, are wound tightly in a row with PEV-2 0.41 wire on a frame with a diameter of 6 mm. As a frame, you can use a high-voltage resistor type C3-14-0,01. Capacitors C1 and C2 can be types KM, KG or KSO.

All elements are mounted on a single-sided printed circuit board 1 made of fiberglass with a thickness of 2,5 mm (Fig. 3. a. b). Dural corners 2 and 3 are riveted to its upper and lower ends. A socket from a ShR-type connector of a suitable diameter is attached to corner 2, and a SR-3-50PV type plug is attached to corner 74. in which the connection element with the coaxial cable was replaced with an insert made of high-impact polystyrene glued from two washers (Fig. 3. c) and a short tube fixing it in the plug housing (Fig. 3. d). The end of the tube protruding from the plug is screwed into the corresponding hole of the corner 3. A short conductor is soldered to the central terminal of the plug. In order to avoid damage to the coils and capacitors and to further strengthen the antenna pin socket, the printed circuit board is placed in a box (it is pushed from above), glued from sheet high-impact polystyrene 2 ... 3 mm thick (Fig. 3. e). The box is fastened to the printed circuit board with two screws (the thread is in the board).

(click to enlarge)

The correct tuning of the antenna can be checked by connecting an SWR meter (preferably a small one) between the antenna and the radio station: SWR should reach a minimum in the operating frequency range. If this minimum is shifted to the region of lower or higher frequencies (in multichannel radio stations this is easy to check), the number of turns of the L2 coil is respectively reduced or increased.

The SWR of the antenna is also affected by the setting of the P-loop. It is specified by shifting-pushing the turns of the coil L1. Experience shows that it is easy to achieve SWR in the middle of the operating frequency range with these procedures. less than 1.1. Antenna bandwidth in terms of SWR 1,5 - not less than 1.2 MHz.

As field tests performed on the Dragon SY-101 radio station showed, the efficiency of the described antenna, compared to the standard one, was 11 dB. which roughly corresponds to a twofold increase in communication range. Such a significant effect is also explained by inaccurate tuning (matching) of the standard antenna itself. So. inclusion of "spiral" Dragon'a through a device similar to the one described above, allowed to increase the signal level at the receiving point by 4 dB. True, in it C1 \u300d 2 pF, C180 \u1d 2 pF; coil winding length L15 - C mm; coil L2 - frameless, contains 0.8 turns wound tightly in a row with PEV-3,3 XNUMX wire on a mandrel with a diameter of XNUMX mm.

Author: Yu.Vinogradov, Moscow

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