Loading ...
Sorry, an error occurred while loading the content.

Direct upconversion WSJT Source

Expand Messages
  • AC TALBOT
    I ve added a new dimension to the WSJT generator / LF DDS source.    A new PIC based DDS design can now generate quadrature outputs for direct upconversion
    Message 1 of 2 , Nov 7, 2011
    • 0 Attachment
      I've added a new dimension to the WSJT generator / LF DDS source.    A new PIC based DDS design can now generate quadrature outputs for direct upconversion in an I/Q upconverter.   This opens up possibilites for beacon sources right up to into the top microwave bands. 
       
      http://www.g4jnt.com/OpticalComms/LF_DDS_Beacon_Source.pdf   has been updated and Annex B to that document gives details of the IQ source using a 16F870 PIC that can generate frequencies between  -10kHz   to  +10kHz
       
      At this moment, I'm transmitting a JT65B beacon signal; on 1296MHz using the IQ output to drive an AD8346  800 - 2400MHz I/Q upconverter.  The simple synthesized LO source driving this was restricted in the spot frequencies it can generate, so while pondering on how to generate a 'nice simple' round number frequency I realised that by programming the DDS with negative numbers, in two-complement, it will generate negative frequencies (automatically swapping the phase on the I/Q outputs to do so).   Although the maths said it would all work properly, it was still rather impressive seeing the DDS work backwards
       
      The DDS internal maths all works properly with two's complement, and the WSJT code generators are just as capable of sending the negative values (typically starting xFF, 0xFE etc ) on the serial interface as normal positive ones.  
       
      Andy
      www,g4jnt.com
       
    Your message has been successfully submitted and would be delivered to recipients shortly.