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.

Some VFO Projects at VK2FC