DMV converter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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The converter allows you to use old-style TVs, as well as 3rd and 4th generation TVs that do not have an ACS unit for receiving UHF.

The converter allows you to view television programs in the decimeter range from the 21st to the 60th channels with conversion to the meter range from the 1st to the 12th channels. The converter is connected to the antenna input of MB TV.

Schematic diagram of the converter is shown in fig. 1. It consists of RF amplifier, mixer, local oscillator.

The radio frequency amplifier is assembled on a microwave transistor VT1 type KT3198B, the converter is assembled on a K174PS4 chip, which is specially designed for use as a mixer.

As a local oscillator, a KT3128A transistor is used, connected according to a common base circuit.

The UHF signal coming from the antenna, selected by the C1, L1, C2 circuit, is amplified by the VT1 transistor, and from the L2, L3 circuit it goes to the D1 chip, where it is converted into meter range frequencies.

The local oscillator operates at frequencies from 421 MHz to 560 MHz. i.e. covers 139 MHz, which allows you to convert any of the UHF channels in the range from 477 MHz to 789 MHz into a meter.

So, for example, to convert the 21st channel into a meter, it is enough to tune the local oscillator to a frequency of 421 MHz, we get 477 MHz - 421 MHz = 56 MHz, i.e. 1st channel, similarly on other channels, while on other channels you can get up to 5 channels of the meter range (see table 1).

Table 1

The converter is powered by a stabilized power supply 9...12 V. Current consumption - no more than 30 mA.

Structural data of the coils are shown in Fig. 2, a drawing of the printed circuit board on a scale of 1: 1 - in Fig. 3.

The converter uses resistors of the C1-4-0,125 type; capacitors C1, C2, C3, C9, C10 - type KD-2, capacitors C4, C5, C6 - type K10-7B, capacitor C7 - type KT-23 8/30 pF, capacitor C8 - from the VHF receiver unit "Ocean" .

The details of the converter are placed on a single-sided printed circuit board made of foil fiberglass 1 mm thick. The converter is placed in the housing of a standard ACS unit. The local oscillator stage is separated from the rest of the converter by a tin partition.

Fig. 4. Adjusting the converter comes down to tuning the local oscillator to the desired frequencies.

At the maximum capacitance of the capacitor C8, by slowly rotating the capacitor C7, the reception of the 21st channel is achieved on the 1st channel, and at the minimum capacitance of the capacitor C8, by the slow rotation of the capacitor C7, the reception of the 60th channel is achieved on the 12th channel.

With this setting, all channels of the decimeter range fall into the conversion band of the converter.

Literature

1. Radio. - 1989. - No. 2. - P.26. 35.

Authors: V. Korobeinikov, Borisov; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Телевидение.

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