Measures... relay. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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Radio amateurs often have difficulty setting up the equipment, and the testers that are at hand do not allow measurements. In such cases, the simplest devices designed by radio amateurs of the 30s will help. Modern details will allow us to simplify their design.
To adjust the boundaries of the receiver range, to check the passage of the RF signal, you can literally assemble a signal generator in a day, the heart of which will be nothing more than an ordinary electromagnetic relay (Fig. 1).
Fig. 1
A few words about how it works. When the power is turned on, relay K1 periodically interrupts the current in the battery-coil L1 (L2) circuit. The ripple current contains a wide range of harmonic oscillations, covering audio and radio frequencies. The last, modulated low-frequency components of the current, are selectively separated by a tunable circuit L1 (L2) - C1 and are fed through an isolation capacitor C2 to the antenna input of the receiver or one of the RF amplification stages. Next, switch S2 selects the desired frequency range.
The device is equipped with a scale and an arrow on the handle of a variable capacitor. It is possible to calibrate the scale of the device according to the scale of the factory receiver, receiving on it the signals coming from the device. Coils for the ranges of medium and long waves can be used ready-made or made independently on paper frames, inside which pieces of a ferrite rod with a magnetic permeability of 600 or 400 are inserted, the diameter of the rods is 8 mm, the length is 25 mm. Winding is carried out with PELSHO-0,1 wire; the number of turns is 90 and 300, respectively.
And here is another design of the device, which will allow you to determine suitability, understand the conclusions, and set the transformation ratio of an existing transformer. It works on the principle of a measuring bridge and is assembled according to the circuit shown in Figure 2. In it, the pulsating current, thanks to the relay K1, passes through the potentiometer R1, to the extreme terminals of which the ends of the two windings W1, W2 of the investigated transformer T1 are connected. While the bridge is not balanced, the buzzer relay signal is heard in the BA1 telephone. Rotating the potentiometer knob, achieve the minimum audibility of the signal. At this moment, for the number of turns in the windings W1 and W2, the resistances of the arms of the potentiometers R' R'', as well as the angles of deviation of the pointer of the instrument U1 and U2, the following formula is valid:
W1/W2 = R'/R'' = f1/f2
If the bridge is not balanced during the measurement, this indicates that the transformer most likely has a fault.
This device uses a high-resistance telephone and a wire potentiometer of the PP-2 type or another with a resistance of 50 ... 100 Ohms, with a power of about 1 W. Use a protractor to calibrate the instrument scale in degrees.
If desired, both devices can be combined together in one housing, since they contain common elements - a power source and a power switch, a relay. By introducing a toggle switch into the combined device, common elements can be switched for one or another work.
Take low-power DC relays, with an actuation voltage of 3 ... 3,5 V, such as RES-9 with a passport RS4.524.203, RES-10 - RS4.524.304, RSM-2 - Yu.17I.81.58. For their normal operation, one battery type 3336 "Planet" is sufficient.
Author: P.Yuriev
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