Two antennas for CB radio. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Two antennas for CB radio. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / HF antennas

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Sometimes radio amateurs try to "squeeze" as much output power out of their radio station as possible, while not paying due attention to the antenna (especially in portable radio stations). But the communication range largely depends on the operation of the antenna-feeder path, on how well it is matched with the transmitter output. The field strength indicator only provides an approximation of the antenna alignment. But with the help of an SWR meter, you can quite accurately tune the antennas, which will be described below. The SWR meter circuit can be taken from [1].

A simple helical antenna can be made on a polyethylene frame from a RK television cable. The workpiece diameter is 9 mm, but a cable with a diameter of 7 mm or more can also be used. Preparation for winding is performed as described in [2]. For winding, a PEV-2 wire with a diameter of 0,5 ... 0,7 mm and a length of 7 ... 7.5 m is taken. In this antenna, a wire with a diameter of 0,64 mm was used. The winding is carried out tightly, coil to coil. The end of the winding is fixed with a strip of insulating tape or "adhesive tape". An SWR meter is connected to the radio station, and an antenna is connected to its socket. The switch is moved to the "reflected wave" position, and in the "Transmission" mode, first 2-3 turns are unwound, and at the end of the setting - half a turn, achieving the minimum instrument readings. It is necessary to avoid the presence of metal objects near the antenna. The accuracy of the setting even depends on the method of fastening the wire (the end of the winding) and the material used (electrical tape, threads, etc.). Therefore, a piece of tape is not removed after the final adjustment. From above, the antenna is wrapped with 1-2 layers of colored adhesive tape ("adhesive tape") 10 ... 12 mm wide. Such isolation has practically no effect on the SWR of the antenna. The use of a protective sheath made of vinyl chloride tube dramatically increases the SWR, and it had to be abandoned.

Better results can be achieved if a telescopic antenna with a matching device is used in the radio station. The length of the antenna ("telescope") is 700 mm. A brass bushing with an M5 thread at the end must be inserted into its base. Thread length -12mm.

Two antennas for CB radio station

Ris.1

Schematic diagram of the matching device is shown in Fig.1. The L1 coil is frameless, wound on a mandrel with a diameter of 6 mm with a PEV-2 wire with a diameter of 0,8 mm and has 9 turns with a winding length. 12mm. Coil L2 contains 30 turns wound with PEV-2 wire with a diameter of 0,27 mm on a Plexiglas frame, made as shown in Fig. 2.

Two antennas for CB radio station
Ris.2

Trimmer core - with M3 thread, grade 30VCh, MP-100, made of carbonyl iron from SB-9a coils. Capacitors C1 and C2 - type KD, KM. All elements are mounted on a board made of one-sided fiberglass 1 mm thick (Fig. 3).

Two antennas for CB radio station
Ris.3

The board is placed in a cylindrical case, machined from Plexiglas. Its drawing is shown in Fig.4. A cut is made in the lid with a needle file for the board.

Two antennas for CB radio station
Ris.4

To tune the antenna, you need to carve another case with a cutout in the middle for tuning the coils. In the CP-50 connector, unscrew the top nut and cut the internal thread M9x1,25 (you can also take M8). Then the nut is screwed with the reverse side onto the case with a cutout, and the board with a piece of PK-50 cable is inserted. The cable braid is connected to a split washer, and the central wire is connected to the pin of the SR-50 connector. Connect the connector and the cylindrical body. The telescopic antenna is screwed into the housing cover and connected to the board with a piece of wire. The body and cover are connected with three M2 screws.

The antenna is tuned using an SWR meter. By shifting and pushing the turns of the L1 coil, the minimum readings are achieved in the reflected wave mode. By adjusting the L2 coil, the setting is refined. This can achieve SWR S1,1...1,2.

And the last thing to do is to transfer the configured matching device board to a one-piece case and make the final assembly.

For correspondence, it is advisable to enclose a stamped envelope in the letter (for residents of Belarus - an envelope without stamps).

Literature

1. Radio, 1996, No. 11.
2. Radio amateur, 1999, N5, p.42.

Author: M.Trotsenko; Publication: N. Bolshakov, rf.atnn.ru

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