VHF FM radio Aurora Millennium. Scheme, description

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VHF FM radio "Aurora Millennium". Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / radio reception

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"Aurora Millennium" is a superheterodyne VHF FM receiver with a low intermediate frequency, assembled on three microcircuits, three transistors and one diode assembly.

The Aurora Millennium receiver is assembled from inexpensive and readily available components. It uses a number of non-standard circuit solutions that improve its consumer properties. In the author's version, the receiver is housed in a housing from a three-program loudspeaker "Aurora" (1971), which determined its name.

The circuit diagram of the radio receiver is shown in figure:

(click to enlarge)

The high-frequency part of the receiver is assembled on a kkha058 microassembly according to a simplified switching scheme. A non-standard solution here is to use, instead of the usual multi-turn variable resistor in such cases, two conventional single-turn ones, such as sp3-4am. A 47k resistor is used for coarse tuning, and a 4k7 resistor is used for fine tuning. Since single-turn variable resistors are much more reliable than multi-turn ones, this increases the reliability of the receiver as a whole. In addition, tuning the receiver with two knobs - "rough" and "fine" - is much more convenient. This idea was taken from the scheme of one of the domestic portable TVs.

With a coil of 7 turns, the receiver covers the VHF-1 range. To rebuild it to the VHF-2 range, you need to reduce the number of coil turns to three.

From the output of the microcircuit, the signal through the volume control goes to the voltage amplifier assembled on one of the six inverters of the k561ln2 microcircuit. Resistors connected between the input and output of the inverter create a DC feedback, thereby transferring it to a linear mode (the logic element "miraculously" turns into an amplifier with a high-resistance input). The capacitor obsoletes the AC feedback so as not to reduce the gain. The idea of such a solution was taken from the article by I. Smirnov and V. Stryukov "Direct amplification receiver ... on a logic microcircuit" from one of the "Radio" issues for 1982 (I don't remember the number).

Next, the signal is fed to a power amplifier assembled on three germanium transistors. Such a simple scheme should not confuse anyone - it really works, and it works well! It should be noted that since the amplifier is single-ended and operates in class A mode, the output transistor should be set to very large heat sink! In the author's version, the p215 transistor was used from the frame scanner of the ULPCT TV together with a standard heat sink (it almost does not heat up with it). The amplifier circuit is taken from the book by V.G. Bastanov "300 practical advice" (M: Moskovsky Rabochiy, 1992), advice number 69.

The power supply of the receiver is made according to the standard scheme based on the voltage stabilizer chip kr142en5a. It supplies the power amplifier with +12V unregulated voltage, and all other receiver stages with +5V stabilized voltage. To protect the receiver from increased voltage in the network, a "transformer tandem" was used, described in V. Kopanev's article "Protection of a transformer from increased voltage in the network" (Radio, # 2, 1997, p. 46.). The ECE KBL06 type diode bridge used in the power supply was taken from a damaged power supply from the 286th PC. It can be replaced with kts402a.

In the author's version, the receiver is assembled by surface mounting on a board made of foil fiberglass. The conclusions of the parts that are connected to a common wire according to the scheme are soldered to the foil, the rest of the connections are made with wires. This idea is taken from the article by V. Polyakov "Spurious communications and pickups in amateur radio structures" (Radio, #2, 2001, p.53 - 55). The high-frequency part is made separately in the housing from the damaged television channel selector SK-D-1, while surface mounting was also used.

The use of a power amplifier operating in class A mode, a sufficiently high-quality dynamic head of the 2gd-38-100 type (from a tube TV) and a large wooden case made it possible to ensure good bass reproduction and abandon the tone control. Despite the relatively low output power (about 1 W), in terms of sound quality (including bass), the receiver is not inferior to portable radio tape recorders of well-known companies.

Scheme in *.SCH format (2,3 kb)

Publication: N. Bolshakov, rf.atnn.ru

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