VHF radio frequency synthesizer control unit. Encyclopedia of radio electronics and electrical engineering

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When repeating the VHF FM radio receiver with a frequency synthesizer described in [1], taking into account corrections and additions [2], it turned out that the frequency synthesizer control unit can be significantly simplified. The new block contains fewer chips and no discrete transistors at all. Dynamic output of information is organized by software without the use of additional chips - code converters and shift registers. Its management is much simpler in comparison with the prototype [1]: it is carried out only by a rotary encoder with a built-in button.

The new block has a much wider frequency tuning range - 45...130 MHz (for the prototype 88...108 MHz) with a step of 100 kHz (for the prototype 50 kHz). It can work in conjunction with tuners VHF-1 (66...74 MHz) and VHF-2 (87,5...108 MHz) ranges, and with a local oscillator frequency both above and below the signal frequency. If the controlled local oscillator cannot be tuned in such a wide range, then when you try to go beyond it, the frequency-phase detector LM7001 will exit the frequency capture mode. In this case, the control of the knob encoder button is provided, pressing which will return the local oscillator tuning frequency to its operating range and, accordingly, restore the PLL mode of the frequency synthesizer.

The scheme of the proposed control unit is shown in fig. one.

Fig. 1

The basis of the block is the DD1 PIC16F628A microcontroller. In accordance with the program, it controls the frequency synthesizer and displays information about the tuning frequency on the four-digit green LED indicator HG1. The last setting of the radio is remembered when the power is turned off. The only control is the S1 encoder with a built-in button. The S1 button has two functions: fixed tuning to a specific radio station (in the author's copy - 100,1 MHz), as well as returning the frequency synthesizer to capture mode.

Fig. 2

All parts are installed on a printed circuit board made of 1,5 mm thick one-sided foil fiberglass. The board drawing is shown in fig. 2. The design used fixed resistors and capacitors - imported surface-mounted: tantalum C1 size "C"; C2 - "B"; C3-ceramic, R1-R3-1206; R4-R11 - 2010 (with a resistance of 0,22-1 kOhm, depending on the desired brightness of the indicator).

The nominal power of SMD resistors of size 1206 is 0,25 W, and of size 2010 is 0,5 W, so this resistor power is indicated in the diagram (see Fig. 1). These resistors were chosen because their length corresponds to the distance between the pads of the printed circuit board (Fig. 2), which, in turn, was adopted due to the need to place printed conductors between them. But the power dissipated on each resistor does not exceed 0,125 W, so surface-mount resistors can be replaced with C1-4 or C2-23 with a power of 0,125 ... 0,25 W.

The HG1 four-digit indicator can be assembled from four separate seven-element LED indicators with both a common anode and a common cathode by combining the same-name outputs of their elements, except for the common ones. Shaft encoder S1 - any with a resolution of 12 steps per revolution, preferably with a button, but in its absence, the button can be separate.

Voltage stabilizer 7805 (DA1) can be replaced by KR142EN5A. Microcontroller PIC16F628A (DD1) - PIC16F627 without changing the program. It is possible to use PIC16F819 with a built-in 8 MHz oscillator. In this case, it is acceptable to use a more accurate encoder (24 or more steps per revolution).

The board provides contact pads for outputting a voltage of 5 V from the output of the DA1 stabilizer, which can be used to power other components of the radio receiver, in particular, the LM7001J frequency synthesizer chip. But it is desirable to apply this voltage to analog nodes through decoupling filters, as shown in Fig. 9 in [3].

Adjustment begins with checking the correct installation. Then the DD1 microcontroller with a pre-recorded program is installed in the panel and the supply voltage is applied. On the display HG1 first appears the line "-" from the elements "G" of each digit, then the elements of all digits go out, except for the youngest. Next, turn off the power and turn it on again, but with the button of the encoder pressed. Again, the line "-" should light up, and then the value of the frequency of the fixed setting "1001" (in hundreds of kilohertz). Next, they check the frequency change by rotating the encoder in both directions and remembering the last tuning frequency when the power is turned off. As a result, when you turn on the power again, now after the line "-" the numbers of the frequency of the last setting should appear. This completes the adjustment - the outputs of the control unit DA, CL and CE can be connected to the corresponding inputs of the LM7001J chip (DA2 in Fig. 2 in [2]).

Microcontroller programs can be downloaded from ftp://ftp.radio.ru/pub/2012/11/lora.zip.

Literature

1. Nosov T. VHF FM radio receiver with a frequency synthesizer. - Radio, 2010, No. 6, p. 16-18.
2. Our consultation. - Radio, 2010, No. 7, p. 60.
3. Ryumik S. Developments of Japanese radio amateurs. - Radio, 2011, No. 10, p. 36, 37.

Author: E. Kondratiev

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