RDF Butterfly Antenna – Radio Direction Finding Antenna

$40 $45

Small form factor, light weight, hand held radio direction finding antenna. An overall size of 11×14 inches (including antenna) and around 100g without battery, makes fox hunting more fun. Current draw is approximate 15mA.  A 9V battery weights in average between 30g to 45g.

Great for walking around, in parks or where you don’t want to carry a big antenna with you. Works on a regular 9V battery with on-board battery holder, BNC connector and 3D-Printed handle.

The operation is quite simple. An electronic switch, formed from two diodes alternately forward-biasing (switching) one of two antennas to the feed line attached to the input of an FM receiver, tuned to the desired frequency of interest. Antenna switching is done at and audio rate at approx.  1KHz. If one antenna is closer to the interference source, it receives the wave at a fraction of a second earlier then the other antenna. This accomplishes a phase difference between the signals received by the antennas. This switching action imposes a phase modulation which will be heart as a tone coming from you receiver.

When rotating the antenna perpendicular to the signal direction, both antennas receive the signal simultaneously thus no phase difference occurs and the audio tone disappears.

Simply, it works by nulling rather then peaking the signal.

Available as a kit or assembled. Assembled version needs to have antennas installed to keep shipping as low as possible.

Kit assembly can take between 30 minutes to 1 hour depending on skills.

*Battery not included*