resonant wavemeter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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When setting up various amateur radio equipment, a resonant wavemeter can provide invaluable assistance. It not only detects the signal emitted by the elements of the device, but also allows you to determine its frequency. The author offers a description of the design of such a device in this article.

To tune the local oscillators of receivers, as well as master oscillators, frequency multipliers and output stages of transmitters, you can use a resonant wavemeter, whose operation is based on receiving energy from the circuit and determining the signal level at a given frequency. By bringing the wavemeter circuit closer to the circuit under study, the signal level is controlled and the circuit is tuned to resonance. As the signal increases, it is enough to increase the distance between the wavemeter and the circuit, the connection between them will decrease. At the same time, minimal losses and minimal detuning are introduced into the circuit, so it does not require further tuning.

The proposed wavemeter has a cylindrical body. In the center of the cylinder there is a capacitor of variable capacity, the axis of which is brought out and a sight is fixed on it, moving along the cylindrical surface. The scales are located on the side surface of the cylinder parallel to the circumference of the base. The replaceable circuit coil is placed at the end of the cylinder, and an indicator is placed at the other end (Fig. 1).

The wavemeter uses a direct-frequency capacitor, in which the stator plates occupy a sector of 90 °, and the rotary ones have a special shape. This made it possible to expand the angle of rotation of the sight to 270°. The coil socket is located in the unused sector 270...360°, closer to the edge of the butt, and therefore does not interfere with the rotation of the reticle.

To improve the frequency reading accuracy, a narrow band is required and, consequently, a high quality factor of the circuit, so the detector is connected to the output from 1/3 of the turns of the circuit coil.

The convenience of the proposed wavemeter lies in the fact that its measuring circuit can be brought closer to the minimum distance to the adjustable contour, since the coil protrudes forward. This allows you to detect a weak harmonic signal. The length of the scales for all ranges is the same, which makes it easier to read the frequency. Due to the use of a direct-frequency capacitor, the scales are linear in frequency. At the same time, the adjustable contour, the wavemeter scale and the measuring microammeter fall into the field of view. In the absence of a direct-frequency capacitor, a conventional KPI can be used. In this case, the scales will be non-linear and shorter in length.

On fig. 2 shows the scheme of the wavemeter: L1 - coil of the measuring circuit; C1 - direct-frequency variable capacitor; RA1 - M4248 microammeter with a total deflection current of 50 μA; VD1 - a diode that performs the function of a detector. The sensitivity of the wavemeter to weak signals can be increased by using a germanium high-frequency diode.

The body of the wavemeter is made of a duralumin tube with a diameter of 65.. .70 mm and a height of 70 mm (Fig. 3). From the ends, disks made of organic glass, getinaks or fiberglass (Fig. 4) are inserted into the pipe, fixed to the cylinder with three M2 screws each. A variable capacitor is fixed on one disk with screws, the axis of which is brought out through a hole in the disk.

On the axis of the condenser at an angle of 90°, a strip of duralumin (Fig. 5) is fixed with nuts, to which a sighting device (Fig. 6), made of organic glass 1–1,5 mm thick, is riveted. When the condenser rotor rotates, the sight moves along the lateral cylindrical surface, on which the scales are parallel. A microammeter RA2 is glued to the other end disk with BF-1 glue.

Replaceable coils are inserted into sockets located on the edge of the upper end of the cylinder. Coils with three leads are placed in plastic cylinders with a diameter of 20 mm from old quartz resonators. A hole is drilled at the base of the quartz cylinder, where the third leg is screwed along the MOH thread. The diameter of the frames of all coils is 12 mm. The coils are fixed on the base of the cylinder with BF-2 glue. The design data of the coils are given in the table. The coils are wound with tension, and after adjustment they are fixed with varnish. Ring inscriptions are made on the cylinders indicating the range number. With the help of five coils, the frequency range from 10 to 180 MHz is covered.

After manufacturing, the wavemeter must be calibrated. To do this, the wavemeter circuit is brought closer to the generator output, an antenna is connected in the form of a piece of wire 30 ... 40 cm long, the generator is tuned to the appropriate frequency and, by rotating the rotor of the wavemeter capacitor, maximum readings are achieved. On a wavemeter scale made of thick paper, they make a risk and inscribe the frequency value. In the same way, all wavemeter ranges are calibrated at the required intervals. By changing the number of turns of the coils, the adjacent ranges are overlapped by 10...15% After calibration, the scale of the wavemeter is covered with mylar film.

When working, the wavemeter circuit is brought closer to the adjustable circuit and, by changing the capacitance of the wavemeter capacitor, the position corresponding to the maximum readings of the indicator is found. The frequency value is read on the wavemeter scale. After adjusting the tuned circuit to the maximum readings, increase the distance between the wavemeter and the circuit to reduce the signal level and adjust the circuit again.

Author: A. Zibitsker, Tashkent, Uzbekistan

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