DDS VFO for the FL-50B Transmitter
The operator of the 1960s Yaesu FL-50B transmitter has the option of using the internal
crystal oscillator, or an external VFO. Yaesu intended that the VFO
in the matching FR-50B receiver could be used as the transmitter VFO. However, VFO stability
problems inherent in the design and construction of this receiver's switched-range VFO
tend to rule out its use for transmit purposes in the 2020s.
I'm willing to accept and work around the rather unstable VFO in the
receiver. However, in fairness to the operator at the other end of my
CW contacts, I have designed and built a DDS VFO for use with the FL-50B
transmitter. My design is based on the work of Paul
The DDS VFO can be seen in the above photo, to the
right of the transmitter.
Here are a couple more photos of the VFO (click on the thumbnail image to
The program runs on an Arduino 'Nano' board, which controls a Si5351
synthesiser. You will notice that the VFO enclosure includes several unused components such as switches,
sockets, and a spare signal buffer/amplifier that are not used in the
current design. They are there to make expansion easier at a later
I'm happy to share the design and software used in this project. The
Arduino code can be downloaded from:
you would like more information, please send me an email, and I'll update
this page accordingly. If you can see improvements to the design,
please let me know!
Digital Board Circuit Diagram
Power Supply Circuit Diagram
Signal Buffer Circuit Diagram
Development of the software was initially carried out using the Arduino
Integrated Development Environment (IDE). This worked perfectly
well. Later, my sons showed me how use Visual Studio Code with the
'Arduino' and Microsoft
'C/C++' extensions. I love Visual Studio Code! My sons
then showed me how to use Git for code
control, and the Xaver Hellauer Clang-Format extension for obtaining
consistent program formatting.
With so many wonderful programming tools available, it's a great time to be
learning how to program -- even at the age of 68! My Arduino 'sketch' (program) is available for download
from GitHub at:
A hardware development and test environment was specifically made for this DDS VFO
project, and similar
projects. Here's a photo of the set-up. It contains enough switches and expansion potential to permit the development of a multiband
transceiver, with full processor-controlled rig control.