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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple antenna current indicator. 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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Since when setting up and coordinating the elements of the antenna-feeder path, it is often more important to notice the growth or decline of the controlled value, the achievement of its maximum or minimum, there is no need to digitize it, to put it in line with some generally accepted units. Such "dimensionless measurements" are the functions of indicators.

The diagram of an indicator suitable for monitoring currents with a frequency of 25 ... 30 MHz is shown in fig. 23.

Here T1 is a high-frequency transformer, the primary "winding" of which is a wire with high-frequency current threaded through its ring core (M50 VCh2-14 K12x6x4,5 mm), and the secondary is 20 turns of wires evenly distributed over the core in plastic insulation. The detector is assembled on the elements VD1 and C1, the resistors Rl, R2 and PA1 make up its load. The pointer device RA1 is a digitized or "blind" microammeter with a total deflection current of 50 ... 150 μA.

The indicator is designed for inclusion in the antenna-feeder path of a transmitter with a power of up to 10W (at R1=R2=1...10 kOhm).

Simple Antenna Current Indicator
Rice. 23. Antenna current indicator

At high powers, the cross section of the transformer core will need to be increased (for a 100-watt transmitter - up to 0,5 ... 1 cm ^ 2; in this case, it will be necessary to increase the resistance of the resistors and, possibly, reduce the number of turns in the winding II of the transformer).

A large core (with a large internal diameter) may also be required to control the current in a "thick" antenna, for example, in a telescopic or helical antenna of a portable radio station.

The indicator can be made in the form of a single block. But it is often more convenient to work with a device that consists of two parts: a detector head "hanging" on the antenna wire, connected by a two-wire line to a microammeter. In order to avoid the possible influence of the communication line on the configuration of the electromagnetic field of the antenna, it can be made of a thin high-resistance wire or placed in it 100 ...

The indicator head is usually placed in the antinode of the antenna current. This not only makes the lead more sensitive, but also minimizes its effect on the antenna.

If the antenna current remains large enough, the germanium diode can be replaced with a silicon one - KD510A, KD522B, etc.

Publication: cxem.net

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