Saturday, April 11, 2015


The original article is being published by VU3ELR , OM SHASHI. he was one of the instrumental organizers for the Ham Fest India 2014 at Hyderabad.
Read the article published in the HFI2013 suverniours. The ino files and ckt is missing but article might inspire you.

How open source can be beautiful and smart.have a   look.


Sasi – VU3ELR

A few  years ago, many  of us  faced  the problem  of constructing  a stable vfo  for  RM 96s, with limited  or no access  to calibration equipment I  had aligned my VFOs with  great  difficulty. With the lack of availability of Styroflex capacitors and NPO capacitors it has become very difficult to make a stable vfo. Being a starter, home-Brewer, I used to search the net for many alternative ideas to make a stable rock bound vfo and finally landed up with no progress as I got QRL with my professional activities.

Although QRL, I never stopped thinking of a good stable vfo that could be used with my RM- 96. I went surfing the net for various solutions and did a little work on some DDS circuits. There are number of circuits available using AD9850, AD9851, Si570..Etc controlled by PIC and other chips. All these circuits are found to be programmed using ASM, Micro C. They need some knowledge in the languages if we intend to do any minor changes to work for our applications. With little bit of working knowledge on these DDS VFOs, I finally thought of developing a DDS VFO that can be programed/modified by an average  Home-Brewer.

Like a lot of Hams, while browsing for electronics on eBay I came across some of these super inexpensive DDS modules being sold  that could be  shipped from China (for about Rs.500/-) These modules are  are far cheaper than the DDS 9850  chip which costs around Rs.1300. .  OM Paddy, VU2PEP initiated the idea and encouraged me try out a DDS with this module I had no second thought and immediately   started working on it and ordered a pair of modules and received the same in less than a weeks’ time

The Circuit:

Before embarking  on this circuit I would like to say that none of these ideas  are mine  and are  taken various references  and sources available  from  well defined circuits of pioneers in home brewing. In this circuit, I have paired my Home-Brew Arduino Uno with AD9850 module purchased online from  on EBay, a 16X2 LCD display, Rotary encoder, and a few other small parts put together making a very descent DDS VFO capable of any frequency between 1Mhz and 30Mhz.  The easiest way to manage the AD9850 is with an Arduino Uno.  A little quick work with a proto-board and I had a nice working VFO.  The schematic shown below is a little rough and I tried my best to make you understand. The circuit is a straight forward and simple  and with a little knowledge on Arduino IDE, The VFO is easy to brew  as short notice “ before you complete your Coke” you can have the up and running  HI

A word about Arduino:

Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for amateurs, designers, hobbyists and anyone interested in creating interactive objects or environments. Arduino can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators. The microcontroller on the board is programmed using the Arduino programming language and the Arduino development environment. Arduino projects can be stand-alone or they can communicate with software running on a computer. The boards can be Home-Brewed or purchased a preassembled and the software can be downloaded for free. The hardware reference designs are also available under an open-source license; you are free to adapt them to your needs.

If you need to know more about the Arduino platform you should check out the official site at  I have been playing with the Arduino for only a couple of months and I already found it to be a fantastic development platform.

PCB Layout and Arduino sketch:

As the source code is unable to put on paper, the required PCB Gerber Files and the Arduino sketch is available on request via mail The low pass filter is directly taken from RM-96. The values of T1, C1 and C2 will change as per the desired operating frequency.


I specially thank OM Paddy, VU2PEP for initiating the idea and giving me a support to complete the circuit. I would also like to thank VU2BVB, VU2CJV, and VU2ZAZ and may others for their valuable feedback and literature.

So, finally there’s no reason why you too cannot have a economical and a efficient  DDS VFO for peanuts  without slogging  and compete  with hams running commercial transceivers and work most of the digital modes which was beyond the working of a homebrewed analog vfo. This DDS VFO can be used as a plug-in replacement for the VFO many  old commercial and valve transceiver like the HW101 SB102 etc and also as useful  signal source for the bench, or as an LO for a direct conversion transceiver … the possibilities are endless!

Happy Home-Brewing.

 The wheel is borrowed from the VU3ELR. If you like it make it. All credit (and blame) goes to him.