04-02-2019, 12:56 AM
Hello everyone,
I have used the module with the AD9833 that Andy had mentioned in this thread. From my experience it is good enough to be used for LW and MW frequencies. I would not use it above 2MHz though, at this frequency the generated sine wave starts to shown the individual steps it's made up of.
The reason why I designed this project is that I wanted to have a stable frequency generator that I could set to deliver certain frequencies that fall into the 9kHz raster of the MW broadcasting band. Especially I needed frequencies that were also multiples of the number 10. The background is that I have several US AM Stereo receivers like the Carver TX11a with PLLs that have a 10kHz tuning step, so I had to find frequencies that can be divided by 9 and by 10 to fit into both the EU and US frequency raster. Such frequencies are ...1080, 1170, 1260, 1350kHz and so on. As it was near impossible to find suitable crystals or even ceramic resonators for these frequencies I decided to use a DDS.
The project consists of the small DDS board with the AD9833 and an Arduino "Mini Pro" that controls the DDS chip. This Arduino board also generates a 25Hz sine wave which is required by AM Stereo as a pilot tone to tell the receiver that it is receiving an AM broadcast in stereo. This is being generated by PWM and subsequent low pass filtering of one of the Arduino outputs.
The design allows the user to select one out of 10 or 16 fixed frequencies that I can program into the Arduino routines by means of a BCD or Hex encode switch.
I would post the code here, but attachments do not seem to work for me, so please send me a PM if your interested in the project. There is also a PCB design available for it...
Semir
I have used the module with the AD9833 that Andy had mentioned in this thread. From my experience it is good enough to be used for LW and MW frequencies. I would not use it above 2MHz though, at this frequency the generated sine wave starts to shown the individual steps it's made up of.
The reason why I designed this project is that I wanted to have a stable frequency generator that I could set to deliver certain frequencies that fall into the 9kHz raster of the MW broadcasting band. Especially I needed frequencies that were also multiples of the number 10. The background is that I have several US AM Stereo receivers like the Carver TX11a with PLLs that have a 10kHz tuning step, so I had to find frequencies that can be divided by 9 and by 10 to fit into both the EU and US frequency raster. Such frequencies are ...1080, 1170, 1260, 1350kHz and so on. As it was near impossible to find suitable crystals or even ceramic resonators for these frequencies I decided to use a DDS.
The project consists of the small DDS board with the AD9833 and an Arduino "Mini Pro" that controls the DDS chip. This Arduino board also generates a 25Hz sine wave which is required by AM Stereo as a pilot tone to tell the receiver that it is receiving an AM broadcast in stereo. This is being generated by PWM and subsequent low pass filtering of one of the Arduino outputs.
The design allows the user to select one out of 10 or 16 fixed frequencies that I can program into the Arduino routines by means of a BCD or Hex encode switch.
I would post the code here, but attachments do not seem to work for me, so please send me a PM if your interested in the project. There is also a PCB design available for it...
Semir
