YO4HFU
PLL 4059 for VHF applications

 

If you need a simple PLL for your VHF:  beacon, repeater, radio link, FM broadcasting , frequency generator, NOAA receiver…here is one solution used many times by me.
No microcontrollers and specialized ICs are necessary, a classic PLL was designed.
Frequency range is between 30-200MHz, parameter limited by prescaler min/max frequency and maximum value of programmable divider. Two steps are available: 12,5KHz and 25KHz.
First download PLL schematic, in this way will be easier to understand my "story".

All components are easy to find. The heart of PLL is the 4059 CMOS programmable divider. I recommend HEF4059 manufactured by Philips (maximum clock ~15MHz at 10V).
LB3500 VHF prescaler circuit was reused from old car receivers with digital scale (frequency meter). In the last instance, LB3500 can be replaced by other prescaler, divider radio must to be 1/8 or 1/16 (in this situation 4013 divider with 2, is not used).
Reference oscillator uses a cheap 4MHz quart and 4060 oscillator/divider. Accuracy of frequency is adjusted using one trimmer capacitor. Of course, for high stability applications is recommended to use TCXO solution.

The frequency step between “channels” can be the new 12,5KHz or standard 25KHz. Performances are betters for 25KHz because 1,5625KHz reference signal is rejected more easy by output low pass filter.
Error signal (tuning voltage) is filtered by two RC low pass filters.  Internal “source follower stage” located in 4046, is used between low pass filters. After some experiments, the last passive RC low pass filter was replaced with one FET active low pass filter. Bellow is possible to see schematic diagram of active output stage. This modification is recommended!

4001 NOR gates and RC integrator are used to detect locked state of PLL. LED output is possible to be connected for switching OFF the transmitter when PLL is not ready and out-band RF signal is generated.
Inputs of 4059 divider are programmed using jumpers, DIP switches or BCD switches (more easy to use). Open position of switch represents logic level 1 (true).  4059 divider can be set between 3 (min) and 9999 (max).  Please see schematic diagram for details regarding switches position.
Multiple frequencies are possible to be selected using diodes matrix. In this way is possible to build a VHF receiver with scaning function or pre-programmed channels. Do not uses high speed scanning, enough time for PLL stabilization must to be ensured. I didn’t measure the necessary time for locked condition.

Central frequency of VCO must to be adjusted in order to obtain “locked “indication and around 4V of tuning voltage. Harmonic content of RF signal needs to be low , in order to ensure correct operation of LB3500 prescaler. Use a simple low pass filter in front of prescaler if the RF signal is rich with harmonics. This advice is useful when you use any IC prescaler. Recommended signal amplitude is around of 150mVrms (maximum 0,6Vrms).

 


PLL 4059 VHF Schematic (2007)
Active FET Low Pass Filter modification
Channel selection with diodes matrix

PCB version - hand drawing


 


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