AD9833 DDS Reference for a 12-18 MHz PLL Oscillator

This homebrew project is a 160-40 meter band SSB/CW transceiver. It has a PLL with a AD9833 DDS reference. The design allows a 1.5 Hz resolution, low noise and flexible frequency management like in most modern transceivers. The photo below shows the control unit. It has a ATMEL microprozessor and a 128x64 pixel graphic display. The above circuit board shows the VCO, PLL and the 10.7 MHz IF receiver with a tunable crystal filter (0.5-3 kHz bandwidth).

The heart of my 160-40m transceiver is the PLL. The AD9833 DDS is the reference oscillator. The VCO frequency is divided by the factor of 16. The result is compared in the phase/frequency comparator 74HC4046 with the output frequency of the AD9833 DDS. The output signal of the phase comparator is filtered in a TL071 operational amplifier low pass filter. The resulting output voltage drives the BB201 varactor diode of the VCO. The AD9833 was chosen because of its low supply current of only 5 mA.


See the circuit diagram of the PLL here.