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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Scanning mode in radio station ALAN-100+. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The radio station "ALAN-100+" and similar ones are among the most accessible and widely used. Unfortunately, they have a limited set of service options. For example, these stations do not have an automatic scan mode that stops on a channel where a signal is present. They are not designed to work in the Russian standard. To introduce it, in addition to changes in the radio station, it will be necessary to refine the front panel to install additional switches. If this is undesirable, you should use the already existing switch designed to turn on the 9th channel.

The proposed revision can also be carried out in those radio stations in which the changes described by the author in the article "Refining CBS radio stations" ("Radio", 1996, No. 12, p. XIV -XV) have already been made.

Scanning mode in radio station ALAN-100+
(click to enlarge)

Schematic diagram of the scanning node is shown in the figure. The device contains an RS-trigger on the elements DD1.1 and DD1.2, a multivibrator on the elements DD2.1 and DD2.2, electronic keys on the elements DD3.1 - DD3.4. In the upper position of the switch SA1 according to the scheme (mode "5", European standard), a high level is supplied to the input 1 of the DD1.1 element, and at the input 6 of the DD1.2 at this time it is low. In this case, the output of the element DD1.1 will be a low level, which will go to the control inputs of the keys DD3.1 and DD3.2. They will be in a high transient state, so relay K1 is de-energized, capacitor C4 is open, and the radio is in mode "5". A high level from the output of the element DD1.2 opens the transistor VT2 and the HL2 LED is on.

In the lower position of switch SA1 according to the diagram, the output of element DD1.1 will be high, the keys DD3.1 and DD3.2 will go into a conductive state and relay K1 will work. With its contacts, it will connect an additional capacitor C4 to the reference oscillator of the radio station. The frequency of the oscillations generated by the generator will decrease and the radio will go into "0" mode (Russian standard). The transistor VT1 will open and the HL1 LED will light up.

If the switch SA1 is set to the middle position, then the RS-flip-flop will remain in the previous state, i.e. the mode "0" or "5" will not change. But a high level will go to the inputs of the DD1.3 element, and a low level - at the output of this element - will allow the signal to pass through the DD1.4 element from the output of the comparator of the radio station's threshold squelch system (IC2 chip). If the output of the comparator is a low logic level, which means there is no signal in the channel, then the output of the DD1.4 element will be high (and the output of DD2.3 will be low) and the pulses from the multivibrator will begin to flow through the DD2.4 element to the control inputs of the keys DD3.3 and DD3.4. Thus, with an interval of 0.2 ... 0.4 s, the keys will close the "UP" button for a time of about 0.02 ... 0.04 s. This corresponds to a tuning time for all channels of about 8...15 s. If you move the SA1 switch to the middle position, the radio will enter the automatic cyclic scanning mode for all 40 channels. Depending on what position the switch was in before, scanning takes place in the "0" or "5" mode.

Automatic scanning occurs until a signal with a level exceeding a predetermined threshold appears in any channel. As soon as this happens, a high level will appear at the output of the radio comparator and the capacitor C2 will quickly charge through the diode VD1. A high level will appear at pin 13 of the DD1.4 element, and the passage of the multivibrator pulses to the control inputs of the keys DD3.3 and DD3.4 will be prohibited. Automatic scanning will stop and the radio will remain on the channel where the signal is detected, as long as the signal is present and even for 1...2 s after it disappears. This is done so that during transmission pauses the radio station would not immediately go into scanning mode. When the signal fails, capacitor C2 slowly discharges through resistor R4, which provides a delay. If the detected signal is of interest to the operator, it is necessary to move the switch to one of the extreme positions and the scanning will stop.

In the extreme positions of the switch SA1, the inputs of the element DD1.3 will be low. So the same will be at the output of the element DD2.4. The keys DD3.3 and DD3.4 in this case have a high resistance, therefore there is no automatic tuning. And so that when switching modes from "0" to "5" and vice versa, the scanning mode does not turn on, the R1C1 circuit is installed.

It should be noted that the described refinement does not disrupt the operation of the radio station in the manual tuning mode by channels. If there is no need for light indication of modes "0" or "5", then transistors VT1, VT2, resistors R7, R8 and LEDs HL1 and HL2 can be excluded.

Almost all parts of the device are mounted on a segment of a unified board. Resistor R1 and capacitor C1 are installed on the terminals of switch SA1 (on the board it is designated SW2). Relay K1 and capacitor C4 are located on the radio board, and LEDs, if necessary, on the front panel. The additional board itself can be attached above the main board at the location of the IC1 chip.

It is permissible to use parts in the device: microcircuits of the K564 series, transistors KT315, KT312, KT3102 with any letter indices, capacitor C2 - K50-6, K53, K52, the rest - KM. Diodes can be any small-sized pulse, relay K1 - RES49, RES60, REK37 with a response voltage of 7 ... 8 V.

A device assembled from serviceable parts does not require adjustment. By selecting capacitor C3, the most convenient scanning speed is set. As for the setting of the "0/5" modes and the installation of the relay, this was described in detail earlier (see "Radio", 1996, No. 12). It may happen that connecting the capacitor C4 to TC1, X1 will lead to a breakdown in generation. Then you need to use a larger capacitor C4 and connect it to another output of the quartz resonator X1.

The radio needs to be done a little refinement related to changing the functions of the switch on the front panel. This switch is double, but its sections are connected in parallel, so you must first disconnect them. To do this, carefully cut the printed conductors going to the switch. In this case, broken contacts between other elements will have to be restored with pieces of the mounting wire. Then the switch is soldered in accordance with the diagram and the device board is connected to the radio station.

Author: I. Nechaev, Kursk; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Civil radio communications.

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