SWR meter for VHF band. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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An increase in the signal frequency leads to an increase in losses in the feeder line. Therefore, it is very important to achieve the best match between the transmitter and the antenna system, namely the minimum standing wave ratio (SWR).

The proposed SWR meter can measure up to the centimeter range in lines with a wave impedance of 50 ohms.

The SWR meter on strip lines described in [1] has a frequency range limitation from above due to the peculiarities of its design, although the circuit design does not impose such a limitation.

The circuit diagram of the proposed SWR meter is similar to that described in [1] and is shown in fig. 1 (differences in the ratings of individual parts).

Ris.1

A feature of the proposed device is the design of the detector part of the SWR meter, which made it possible to extend the measurement range up to 1 GHz.

The author omits a description of the physics of the formation of standing waves in connecting lines, mathematical calculations of the values ​​of the incident and reflected powers for a matched and non-matched line, the principle of measuring SWR based on measuring certain values ​​of the incident and reflected waves, the fundamentals of designing microwave devices and the technological requirements for to them, and refers interested readers to the well-known literature [2,...6].

Design

The body of the detector head of the SWR meter consists of two parts (Fig. 2): U-shaped base 1 and cover 2 (material - bronze).

Fig.2 (click to enlarge)

The design of directional couplers 3 (L1 and L2) is shown in Fig.3.

Ris.3

Center conductor 4 (L2) is soldered directly to connectors XS1 and XS2. Glasses 2 (5 pieces) and four glass beads 4 are soldered into the cover body 6. Diodes (VD1; VD2), capacitors (C1; C2) and resistors (R1; R2) are placed in cylindrical glasses 5. The diode leads are passed through the glass beads channel and soldered directly to the taps.

The body of the detector head of the SWR meter, directional couplers, and the central conductor are polished before assembly (in the case - only the inner surface with a diameter of 15 mm; the outer surface with a purity of Rz 20) and coated with silver.

Assembly order

First, install all the parts related to the cover of the detector head. Then, one of the XS connectors with a soldered center conductor is fixed at the base of the head, then the second connector and soldering is carried out. After assembling the base and cover, they are connected using 6 M3 screws, and connectors XS1 and XS2 are fixed in the cover.

Before assembly, rinse the detector head with alcohol and dry. Work in cotton gloves, after degreasing the skin of the hands.

Details

Requirements for radio elements are standard for microwave technology. Capacitors C1 and C2 are through. In the author's version, frameless diodes AA113A are used. It is possible to replace with other types of diodes depending on the required upper cutoff frequency. In this case, it is possible to use a different method of their fastening! Connectors XS1 and XS2 are of silver-plated design; their type is determined by the outer diameter of the cable.

Notes

1. When using a cable with a characteristic impedance other than 50 ohms, the diameter of the center conductor is calculated using the formula:

Zo=138lgD/d

where: Zo is the wave impedance of the line, D is the inner diameter of the screen of the coaxial line of the detector head, d is the diameter of the central conductor. The values ​​of the resistors R1 and R2 are brought into line with the characteristic impedance of the cable.

FROM THE EDITOR. It is possible to simplify the design of the proposed SWR meter by using a coaxial line with a square screen section and a round central conductor. The calculation of the line dimensions can be performed based on the formula:

Zo=138lg1,08D/d

where: Zo is the wave impedance of the line, D is the inner side of the square screen of the coaxial line, d is the diameter of the center conductor.

2. It is necessary to accurately maintain the dimensions of the parts, the type of connection, as well as the mounting dimensions.

3. For convenience, the detector head can be structurally combined with the indicator part in a common housing.

4. If the radio amateur does not have ready-made glass buses at his disposal, then you can use suitable sizes by dismantling them from metal-paper capacitors.

Literature

1. I.Ya.Milovanov. SWR meter on strip lines. Radiohobby, No. 6, 1998 With. 16.
2. Radio, television, electronics, N 1,1985, XNUMX. (NRB).
3. S.G. Bunin, L.P. Yaylenko. Handbook of a shortwave radio amateur, ed. 2, per. and add., Kyiv, Technique, pp. 221,243.
4. S.M. Alekseev. VHF amateur radio equipment. State. energy publishing house, M., - Leningrad, 1958, p. 131.
5. M. Levit. A device for determining SWR, Radio, 1978, N 6, p.20.
6. Technical description and diagram of the electrical circuit radio station "Len".

Author: Ivan Milovanov, UYOYI, Chernivtsi; Publication: N. Bolshakov, rf.atnn.ru

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