Project: PC Controlled 2-250 MHz RF Source


Featured on the cover of QEX, January 2000


Design Services Performed:


 This demonstration project was designed to prove out a wide range, high resolution hetrodyned RF source concept. Using two PLL's and a DDS synthesizer this source has 1 Hz resolution over the full 2 to 250 MHz output range. The PLL modules are 500 to 750 MHz, VCO based designs that are hetrodyned to get the output frequency range. Excellent phase noise and spurious response performance is also achieved using the DDS driven PLL approach. Also included in the design is a novel output leveling circuit which provides -15 to 15 dB output range with 0.5 dB accuracy over the entire frequency range. The source is really a virtual instrument with all it's functions being controlled by a PIC Microcontroller via an ActiveX enabled PC control program. Communications to the PC is via a speedy 19.2 k Baud RS232 link operating in a 4 byte packet mode for speed reasons.

  • 2-250 MHz output range with 1 Hz resolution.
  • -15 to +15 dBm output range (leveled).
  • Full frequency and output amplitude e-calibration built in.
  • PC Control via an ActiveX enabled virtual front panel.
  • RS232 communication (or USB) link to the PC.
  • On board PIC Microcontroller.
  • Spurious responses below -60 dBc.
  • Harmonics below -40 dBc.
  • Phase noise = -96 dBc/Hz at 10 kHz offset.
  • Wide band signal path, no switching from 2-250 MHz (7 octaves).
  • Shielded, modular design.


A full PCB set was published with the design. Above is the top and bottom of the Mixer / Output stage. High performance was achieved using a very basic 2 layer design mixing surface mount and through hole components as required to optimize the cost.



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