AD9850 module based HF and 2m DDS VFO

A VFO which can generate LO in HF and VHF bands is described in this post. The VFO will be useful for antenna analyzer. This VFO is also planned to be used in a high power signal source for HF & VHF SWR + Power Meter testing. AD9850 module available of the Ebay makes things simpler.

AD9850 DDS Module pinout

AD9850 Module Schematic

The AD9850 DDS module has 2 sine outputs - one filtered output and another is unfiltered. The filtered output is has an 70MHz elliptic low pass filter. The AD9850 DDS module uses a 125MHz DDS clock. The filtered output can be used to generate 0 to 30MHz output. VHF output (2m) falls in the 3^rd Nyquist Zone (2^nd Image) . For example to generate 145MHz, program the DDS for (145MHz - 125MHz) = 20MHz. However, to generate the VHF output, we need to add a bandpass filter, which allows 140MHz to 150MHz output. The bandpass filter should have notches at 125MHz and 187.5MHz.

Example VHF Bandpass Filter for 2m