VHF radio frequency synthesizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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VHF radio frequency synthesizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Frequency synthesizers

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When working on the design of a VHF radio station, I faced the task of building a simple frequency synthesizer 144 - 146 MHz.

Looking through the designs of different synthesizers, I came across the synthesizer of Mikhail Kislinsky (RX9CBI). I really liked this design for its simplicity, the absence of scarce components. However, I was not satisfied with the control using the switches. Therefore, I decided to finalize the scheme, introduce a number of additional features into it. In the process of finalization, the circuit diagram was changed only cosmetically, it is still based on the RX9CBI circuit, and the program had to be completely rewritten.

So what's new:

unlike the original scheme, control is carried out using four multifunctional buttons,

sound confirmation of pressing buttons is introduced,

frequency indication was introduced using a liquid crystal indicator from an imported phone,

a variable frequency step has been introduced, with the frequency can be changed in steps of 25/100 kHz or 5/20 kHz,

A microphone amplifier is included in the circuit.

As in the original design, the operation mode with a frequency spacing of 600 kHz through a repeater was left.

(click to enlarge)

Brief explanations for the scheme.
J3 - contact for connecting the frequency increase button by 25 kHz (+25)
J4 - contact for connecting the button to reduce the frequency by 25 kHz (-25)
J6 - contact for connecting the frequency increase button by 100 kHz (+100)
J7 - contact for connecting the button to reduce the frequency by 100 kHz (-100)
the second contacts of the buttons are connected to the "common" wire of the synthesizer.

Simultaneously pressing the +25 and -25 buttons switches the synthesizer to repeater mode. In this case, the letter "P" appears in the leftmost digit of the indicator. Pressing these two buttons again returns the synthesizer from repeater mode to normal mode and the letter "P" in the left digit of the indicator disappears.

Pressing the +100 and -100 buttons simultaneously switches the tuning step. After that, buttons J3 and J4 tune the synthesizer to +5 and -5 kHz, respectively, and buttons J6 and J7 to +20 and -20 kHz. Pressing again returns the synthesizer to 25/100 kHz tuning mode.

On switching on: the repeater is switched off, the frequency is 145300 (common channel in Tambov), the tuning step is 25/100 kHz.

Contacts J9, J10, J11 - LCD connection from "Panaphone."
Contacts J12, J13 - control of pressing buttons. A piezo buzzer from Chinese phones is connected here.
Contact J14 - switching reception - transmission. Transmission - log. "0".
Contact J15 - microphone input.
Contacts J1, J2 - synthesizer power supply.
Contact J5 - output "capture". Can be used to block the transmitter when the PLL is not locked.
Contact J8 - synthesizer output.

The synthesizer is made on a single-sided printed circuit board with jumpers. This is done due to the fact that in amateur conditions it is difficult to make a double-sided board with hole plating. It's easier to solder a few jumpers.

VHF radio frequency synthesizer

The program for self-production of a synthesizer can be taken here.

I express my deep gratitude to M. Kislinsky (RX9CBI) for his help in working on this design.

Author: A. Denisov, Tambov; Publication: N. Bolshakov, rf.atnn.ru

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