Homebrew VFO Projects
Amateur Radio Station VK2FC
Si5351A based VFO
This VFO is based on the Si5351A Etherkit breakout board from NT7S. It's fitted with the TCXO option as the reference.
Etherkit Si5351A Module
Arduino Nano & Si5351A
Motherboard and Filters
Complete Assembly
The motherboard is home made and my original version has an AD9850 module located in the same location as the Etherkit module. The usual 2 x 16 LCD display and a connector on one end of the board for additional I/O functions if required.
This version of the VFO is configured with a 41-43MHz output from CLK0 and a 9MHz BFO output from CLK2.
Below is a spectrum analyser display of the 9MHz output from CLK1 before and after filtering to remove harmonics. I used a 2 stage lowpass filter for this output. Click on the image for a closer view.
Below is a spectrum analyser display of the 41-43MHz VFO output from CLK0 before and after filtering to remove harmonics.  I used a 3 stage bandpass filter for this output. Click on the image for a closer view.
9 MHz BFO Carrier from Si5351
41 MHz VFO Carrier from Si5351
An AD9851 VFO
I think it is important to have as 'clean' an oscillator signal as possible to minimise unwanted mixing products appearing at the output of a mixer
Page last updated 13 April 2018
This VFO is intended for use in a 6 metre SSB radio project that utilises a 9 MHz I.F. Frequency
I have purchased a few of those AD9850 DDS modules from China via eBay and used them in a couple of VFO projects. I had noticed that some sellers offer AD9851 modules so thought I'd purchase a couple.  Unfortunately each time I ordered the AD9851 type the AD9850 version would eventually arrive in the mail. The best I could do was to receive a refund as the sellers were not able to supply the item they advertised. The same sellers continue to advertise AD9850 as AD9851 and get away with it!

On one occasion I was lucky and managed to order and receive the AD9851 module.  I have fitted one of the modules onto my VFO motherboard and set it up to operate as a 41-43 MHz VFO. I may use this one too in a six metre radio project one day. The images below show the output of the AD9851.