Frequency synthesizer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Frequency synthesizers

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The synthesizer is designed for a transceiver with a single frequency conversion and generates a frequency grid in 61 hertz steps for 9 amateur bands. The frequency indication is accurate to 100 hertz. On bands of 10 MHz or less, the local oscillator frequency is higher than the receive frequency by the value of the intermediate frequency, and on bands of more than 10 MHz it is lower. The value of the intermediate frequency is written to the K573RF5 chip during its programming and can be any from 0 to 13 MHz. The design is made on 4 boards. Board A1 is a processor module and a local oscillator control module; A2 - local oscillators and phase detector; A3 - keyboard and display; A4 - encoder. The processor module through the input-output ports of the PD7, DD8 microcircuits provides full control of the synthesizer.

The program is written in the assembler of the KR580IK80A processor, so it can be used instead of the Z80. The local oscillator control module includes a divider with a fixed division ratio DPCD and a divider with a variable division ratio DPCD. DPDKD is made on DD9, DD10 microcircuits and divides the frequency of 1 MHz, stabilized by quartz, to the reference frequency of 244 Hz, which is fed to one of the inputs of the phase detector. DPKD is made on microcircuits DD11...DD16. The DPKD should also include a 193IEZ counter located on the local oscillator board. The binary frequency code from the processor module is supplied to the presetting inputs of the DPKD counters. From the output of the DPCD, the signal is fed to the second input of the phase detector.

The signal from the output of the phase detector (DD1, DD2.1, DD2.2, VT1, VT2) is fed through a low-pass filter (R6, R8, R9, C1 ... C4) to the varicaps of seven local oscillators. Of these, only one is enabled by the DD3 decoder. The input of this microcircuit receives the binary code of the range from the processor module. The transceiver uses this code to select a band filter. Nine decoder outputs correspond to nine amateur bands. Since there are only seven local oscillators, some of them are used on two bands if the frequencies required from the local oscillators on these bands are close. The correspondence between ranges and local oscillators is set by jumpers.

The diagram shows the position of the jumpers for an intermediate frequency of 5,5 MHz. In reality, the local oscillator generates a frequency four times higher than the required one and the frequency grid step is equal to the reference frequency applied to the phase detector, i.e. 244 Hz. The divider by 4 on the DD4 chip lowers this frequency to the required one, reduces the frequency grid step to 61 Hz, and also stabilizes the output signal amplitude. When using the reference frequency of 244 Hz, it was possible to achieve an acceptable synthesizer tuning speed. So, changing the frequency from one end of the amateur band to the other is carried out in less than 1 second. And with normal detunings less than 10 kHz, this happens unnoticed by the operator. On the elements DD2.3 and DD2.4 assembled signal shaper "LOCK". The signal is used to indicate that the actual output frequency of the synthesizer matches the display readings.

Synthesizer circuit. Picture 1

Synthesizer circuit. Picture 2

The operator controls the synthesizer by means of the keyboard, encoder shaft and the gear switch button. The keyboard can be conditionally divided into three groups. The keys of the first group Al ... A7 control the signals at pins 3, 2,1, 40, 39, 38, 37 of the DD7 chip of the Al board. When you press any of these keys, the logic level on the corresponding output is reversed. This allows you to use this group of keys, for example, to turn on the attenuator, VOX system, CW mode. Another group of keys consists of two (-> and <-), pressing which leads to a quick tuning of the synthesizer up or down in frequency. The third group includes 10 multifunction keys. They are used to issue a command, to select a range, or as numbers from 0 to 9.

Ris.3

Table 1. List of elements of local oscillators #1 ... # 7, the values ​​\u5,5b\uXNUMXbof which are indicated on the diagram, for an intermediate frequency equal to XNUMX MHz

The inductors L are wound with PEV 0.5 wire on frames 5 mm in diameter with ferrite cores.

Let's take a look at each team. To select a range, press the "D" key and the key with the desired range. Setting any frequency from the keyboard is done by pressing "F" and entering the frequency value using the keyboard in numeric mode. To store the current frequency in one of the 10 memory cells, use the "IN" key and one numeric key indicating the number of the memory cell. Retrieving the frequency from the memory occurs after pressing the "OUT" button and one digital one - with the cell number. Before giving the scan command, the values ​​of the boundary frequencies of the scanning range are entered into the memory cells with numbers "0" and "9". To issue a command, the "S" button is pressed. After a small turn of the encoder, scanning stops. If you give the command again, the process will start from the interrupted place. The synthesizer's memory has 8 memory locations used as a stack.

The current frequency is written to the stack automatically in the following cases: when a new range is selected, when a frequency is retrieved from a cell, when a frequency is set from the keyboard. Returning the frequency from the stack is done by pressing the "W" key. By repeatedly pressing "W", you can view all the frequencies in the stack. Turning the detuning on and off is done with the "R" key. If detuning is enabled at the far left of the display, the "-" sign is lit. All of the following commands only work when detune is enabled. The exchange of places of the current reception frequency with an additional reception frequency is performed by the "A - B" key. The exchange of places of the current reception frequency with the transmission frequency is carried out by the key. "R-T". With the "TR" key, you can make the transmit frequency equal to the receive frequency.

You can read about the requirements for the design of the synthesizer in the Radio magazines for 1990 NN 1, 2, 3. The setup should begin with checking the printed conductors for integrity and for the absence of short circuits between them. This operation should be carried out with particular care in the processor module. Since it is almost impossible to determine the malfunctions in the processor module with an oscilloscope or a tester, it is recommended that the DD2, DD5 ... DD8 microcircuits be placed on panels or peppers by soldering to first determine their performance. When repeating the design, please note that on the A1 board, pin 15 of the DD14 chip is connected to pin 7 of DD15. This is not a typo.

After "revitalizing" the synthesizer, most likely you will have to adjust the tuning ranges of the local oscillators. To do this, on each amateur band, the values ​​\u1b\u9bof the lowest and highest frequencies are entered from the keyboard. In this case, the voltage on the heterodyne varicaps should be in the range from XNUMX to XNUMX volts and the "LOCK" LED should be off. Otherwise, you will have to pick up the elements marked with asterisks in the diagram.

Ris.4

The mechanical part of the encoder consists of a shaft and a cover (made on a lathe from steel), two bearings, a grover, a washer and a nut. With a frequency grid step of 61 hertz and with 30 holes on the shaft drum, one turn of the encoder changes the frequency of the synthesizer by 30x4x61 - 7320 hertz.

The author has the opportunity to distribute a printout of the program and will respond to letters with enclosed envelopes.

Author: A. Suharuk, Kovel; Publication: N. Bolshakov, rf.atnn.ru

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