The RDF42 pseudo doppler radio direction finder;
This RDF42 is my latest development, featuring:

All important settings stored in 32 presets.
One knob controls all settings, using the built-in or remote encoder/switch.
Soft commutation, +/- 1 degree processing accuracy.

An instruction video can be seen here:



  • Professional soft switching for highly reduced noise floor.
  • Works as a Pseudo Doppler as well as an Amplitude direction finder.
  • High sensitivity: Suitable for weak signals.
  • Accuracy in good conditions, using a UHF doppler array: 2,2 degrees averaged.
  • Wide frequency range, 30MHz-1GHz depending on antenna array.
  • Several antenna array designs available.
  • Dual mode: Adaptive Averaging mode for mobile applications, Burst mode for catching very short transmissions.
  • Quality weighing of measurements, using the best measurements to generate a stable long time average.
  • Automatic Adaptive Averaging continuously optimizes the amount of averaging in the current situation.
  • Best measurements are automatically sent over USB to computer in order to plot bearing lines on map. (mapping program available)
  • Clear 128×64 pixel display, perfectly readable even in bright daylight.
  • On screen symmetry indicator, gives instant insight of multipath distortions.
  • Bearing pelorus showing the four last measurements plus long time average.
  • Digital display of long time average and quality factor.
  • Automatic display freeze below set squelch point.
  • Elevation indicator for airborne sources. (not suitable for short signal bursts)
  • Antenna test mode.
  • Built-in audio amplifier with volume control.
  • Built-in speaker.
  • Runs on 12V power supply or car battery, consuming less than 200mA.
    (8V up to 14V dc, Minus pole connected to mass)
  • Reverse polarity protected.

The RDF42 fundamentally works the same way as the RDF41 does, the big difference however is the possibility to adjust and store all important parameters.
This enables optimized performance in a very wide spectrum of direction finding activities.
For working principles please see the RDF40 and RDF41 page.

We’ll zoom in now on the adjustable parameters of the RDF42.