Digital scale with indication correction. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Digital technology
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The use of digital scales allows, at low cost, to significantly improve the accuracy of the reading devices of transceivers and receivers. One of the simplest options for constructing a digital scale is the option of measuring the frequency of a tunable local oscillator (GLO) [1, 2]. This method is often used in VHF transceivers. Measuring the frequency of the "stand" local oscillator, which carries the generated signal to the operating frequency (144, 430 MHz, etc.), and summing it with the frequency of the GPA and IF, requires high-speed and, therefore, expensive digital microcircuits. But they are not available to everyone. Therefore, often the digital scale provides an indication of only hundreds, tens and units of kilohertz of the GPA frequency. Indicators displaying units, tens and hundreds of megahertz are controlled by a switch associated with the range switch, but not related to the logic of the digital scale.
A certain inconvenience in this case is the need to select the frequency of the "stand" local oscillator such that the beginning of the range, for example, 144,000 MHz, corresponds to zero values of hundreds, tens and units of the GPA frequency. It is often difficult to fulfill this condition due to the inability to purchase quartz resonators for the required frequency. So, for example, on the two-meter range, when using a 10,7 MHz quartz filter and changing the GPA frequency from 11 to 12 MHz, the frequency of the "stand" quartz local oscillator should be 122,3 MHz. On the 70 cm band, its frequency should be 410,3 MHz.
The cardinal solution to this problem is to use a programmable counter on a 561IE11 or 564IE11 chip. This counter allows, when a combination of logical 2 (ground) and logical 4 (+ 8 V) is applied to its inputs Dl, D0, D1, D9, to write a number from 0 to 15 in each bit. At the same time, supplying 0 or 1 to the input of the counter "+1", you can add or subtract the recorded number from the measured frequency of the GPA. So, for example, the frequency of the quartz local oscillator in the two-meter range was 121505 kHz for the author. This was achieved by multiplying nine times the oscillations of a 13500 kHz quartz resonator from the UW3DI transceiver kit (40 m). In this case, the GPA frequency at the beginning of the range (Fd = 144000 kHz) will be:
Fgpd \uXNUMXd Fd - Fkv.g - Fpch,
where Fkv.g - the frequency of the quartz local oscillator "stand"; Fp - intermediate frequency. As a result, Fgpd = 144000 - 121505 - 10700 = 11795 kHz.
In order for the indicator to have zeros in place of hundreds, tens and units of kilohertz when tuning to a frequency of 144000 kHz, the number 205 must first be written into the counter. The desired combination is dialed according to the table.
Logic 0 corresponds to the shorting of the inputs D1-D8 of the counter to the case, and 1 - to the supply of voltage +9 V to the inputs.
A schematic diagram of the proposed digital scale is shown in the figure. Fragments of the scheme from [2] were used in its development. The scale as a whole is made traditionally, so we will report only its features. The circuit from C6R8 provides, when turned on, the installation of the K176IE4 dividers in the initial state. As switches SA1-SA12 it is very convenient to use small-sized switches VDM1-4 used in computer technology devices. They easily allow you to set the required numbers in the counters DD8-DD10.
(click to enlarge)
(click to enlarge)
The diagram (Fig. 1a) shows the option of connecting the high-order indicators of the 2-meter range. Pin 1 of the indicators is permanently connected to a + 9 V source, and pins 2 or 3 are supplied with + 9 V voltage through a switch, depending on the included 144 or 145 MHz range, respectively.
In the same place (Fig. 1b), with the preservation of the reference designations of the elements, the option of connecting indicators for the 70 cm range (432 or 435 MHz) is shown.
Structurally, the scale is made on a double-sided printed circuit board 150x57 mm in size using hanging conductors (based on the principle described in [1]). The VDM1-4 switches are installed on a separate board above the DD8-DD10 microcircuits and are connected to the last wires. LED indicators HG1-HG6 are conveniently mounted on 50x30mm plates with universal printed wiring and connected to the main board with a flexible cable.
If the GPA frequency does not exceed 14 ... 15 MHz, you can try to reduce the scale supply voltage to 7 V. This will reduce the current consumption to 150 ... 160 mA.
Literature
- The best designs of the 31st and 32nd exhibition of radio amateurs. - M.: Ed. DOSMF USSR / VHF transceivers "Graviton 144" and "Graviton - 432", p. 90-101.
- Chalyshev L. Amateur connected KV. receiver. - M.: Radio, 1982, N10, p. 17-21.
Author:A. Sablin (UA4FP), Penza; Publication: N. Bolshakov, rf.atnn.ru
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