Label generator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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The described generator provides a wide range of signal harmonics, extending up to 500 MHz with a resolution of 100 kHz, 1 or 10 MHz. It can be used to calibrate scales and measure the sensitivity of radio receivers, and can also be used in conjunction with a swept frequency generator to form marks.

The scheme of the device is shown in fig. 1. On the logic element DD1.1, a master oscillator is assembled at a frequency of 10 MHz, stabilized by a ZQ1 quartz resonator. Its circuit is quite traditional for CMOS oscillators, however, an L1 choke is installed in series with the resonator. Without it, the generated frequency in such a switching circuit is higher than the nominal one.

Two ten-day frequency dividers on DD2 and DD3 microcircuits are connected to the generator output. The KR1554 series has KR1554IE6 counters with the required conversion factor, but the author failed to purchase them, so the dividers are assembled on binary counters that are part of the KR1554IE23 microcircuit. The elements of the DD3 chip provide a reset of the counters when they reach state 10 and the corresponding conversion factor. The choice of counter inputs and outputs for taking a signal from them is mainly due to the convenience of PCB layout.

Element DD1.2 - buffer. From its output, pulses with a frequency selected by the SA1 switch (100 kHz, 1 or 10 MHz) are fed to a shaper made on elements DD1.3 and DD1.4. Element DD1.3 inverts pulses with a delay of approximately 3 ns. Therefore, with a positive drop at the output of the element DD1.2, a high logic level is set at the inputs of the element DD1.4 for the delay time, generating a low logic level pulse of the same duration. Such pulses have a wide frequency spectrum with a resolution determined by their repetition frequency, which, as mentioned above, can be 10 MHz or 1 kHz.

Capacitor C6 serves to eliminate the constant component in the output signal, and elements C7 and R4 sharpen the pulses somewhat and even out their spectrum.

The generator supply voltage is 8 ... 12 V, and the voltage supplied to the microcircuits is 5 V, it is stabilized by the DA1 stabilizer. The output impedance of the generator is slightly less than 50 ohms due to the shunting of the resistor R5 by the output resistance of the element DD1.4. If there is a need for an output resistance of 50 ohms, you can increase the resistance of the resistors R4 and R5 to about 75 ohms, while it is necessary to control the output resistance by known methods.

The generator is assembled on a printed circuit board made of fiberglass with a thickness of 1,5 mm (Fig. 2). On the side where the elements are installed, the foil is preserved and divided into two parts along the dashed line. Its lower part plays the role of a common wire, the upper one - the power bus. Holes other than those marked in fig. 2 crosses, meaning soldering to the foil of a common wire, are countersunk on the installation side of the elements to exclude possible contact with the leads of the parts. A quartz resonator in a glass case is fixed on the board with a wire bracket soldered into the holes of the board. To connect to a battery or power supply and solder the output cable, pins with a diameter of 1 mm from the 2PM connector are soldered into the printed circuit board.

The KR1554LA3 chip is quite unique for use in the driver of this device - it can be replaced equivalently only with other microcircuits of this series that perform the functions of NAND or NOR (in the latter case, the unused input of the DD1.1 element should be connected to a common wire), or to its imported analogue - 74AC00. You can try to replace it with KR531LA3 or KR1531LA3, but the results of such a replacement are not obvious. The KR1554IE23 chip without processing the printed circuit board is replaceable by K555IE19 or KR1533IE19, in this case, K3LA555 or KR3LA1533 should be put in place of DD3. In place of DD2 and DD3, one K555IE20 chip or two any counters with a conversion factor of 10 - K155IE2, K155IE6, K155IE9, K155IE14 and their corresponding chips of the K555, KR1533, KR531, KR1531 series are quite suitable.

The generator used resistors MLT-0,125; capacitors - KM-5 or KM-6, C3 and C4 - leadless K10-17v or other similar ones. In their absence, it is permissible to install KM-5 or KM-6, shortening, as far as possible, their conclusions. Switch SA1 - VDM1-2, throttle L1 - DM-1,2.

If the generator has all CMOS chips, you can use a 6 V stabilizer - KR1157EN6, KR1180EN6 with any index, as well as the 7806, 78M06 or 78L06 series. If the generator is built into a device with a suitable supply voltage, it is not necessary to install the DA1 chip.

Setting up the device is reduced to setting the frequency of the master oscillator by selecting the capacitance of capacitors C1 and C2 and, if necessary, the inductance of the inductor L1. It should be controlled by a frequency meter connected to the output of the DD1.2 element so that the input capacitance and resistance of the device do not change the generator load. The frequency stability of the marker generator is actually determined by the stability of the quartz resonator within the operating temperature range of the device.

The spectrum of the output signal of the generator is very wide. On fig. 3 shows the dependence of the level of the spectral components on the frequency with the appropriate discreteness of the labels set by the switch SA1.

Up to a frequency of 100 MHz, the amplitude unevenness is not more than 3 dB, which makes it possible, by supplementing the generator with an attenuator, to use it to measure the sensitivity of radio receivers with sufficient accuracy. At higher frequencies, the drop in the amplitude of the tags is about 10...12 dB for every 100 MHz.

Author: S. Biryukov, Moscow

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