3 Element Yagi Direction Finding Antenna for 70cm / 433MHz

Foldable 3 Element Tape Measure Yagi Antenna for Amateur Radio Direction Finding

• Very good F/B ratio for easy direction finding

• Ideal for Draussenfuchs [1] or Amateur Radio Direction Finding (ARDF)

• Light weight (around 70g, without cable)

• Easy printing

• Small packing size when folded

Radiation pattern

Dimensions

• Reflector: 34.6 cm length @ 0 cm

• Radiator: 30 cm length @ 12 cm

• Director: 28 cm length @ 23 cm

Needed Parts

• At least 33 cm plastic electro installation pipe (16 mm diameter) as boom

• At least 92.6 cm tape measure (width 12 mm, e.g. IKEA TRIXIG [2])

• 10 cm heat-shrink tubing WITH glue (15 mm diameter; variant WITH PCB can be 12mm)

• 75 cm heat-shrink tubing WITHOUT glue (12 mm diameter)

• Superglue

• 6 zip ties 100x2.5 mm (optional)

• 3D printed element holders (check variants below)

  • 2x holder for reflector and director (both use the same model so print twice)

  • 1x holder for radiator

• approx. 75 cm coax cable with BNC/SMA connectors

• Optional: 3D printed belt clip holder for Quansheng UV-K5/6 and K1

Variant with PCB

• For an easier cable connection a PCB for the radiator elements was made by DK4HAA for the draussenfuchs project [1].

  • Get gerber here: [3]

• If you do not have this PCB use the variant below.

• The distance between both radiator elements on the PCB is 0.9 cm, so one element must be (30-0.9)/2 = 14.55 cm long.

• Remove the paint from the measuring tape and solder it carefully to the PCB before assembly of the other parts. Take care to align the radials parallel to the PCB edge and as flat as possible on the PCB surface.

• Use the 3d files named "*WITH_PCB*" if you have this PCB.

• A rubber band can be placed around the PCB for extra stability if you like. Place it there before glueing the 3D printed parts on the boom.

  

Variant without PCB

• Cable connection is either done by

  • spot welding (normally used for welding batteries together, more robust but less common)

  • OR soldering (less robust but easy available)

• No PCB is used in this version.

• Remove all the paint from the measuring tape in the contact area.

• Do not solder the coax cable directly to the measuring tape, place a short flexible wire in between.

• The distance between both radiator elements is 0.4 cm, so one element must be (30-0.4)/2 = 14.8 cm long.

• Use the 3D files named "*WITHOUT_PCB*" if you don't have the PCB.

• Heat shrinking tube with glue must be 15mm diameter, 12mm is too small.

Model files depending on printer precision

• The default push through gap for the tape measure is 0.5 mm. Normal printers with 0.4 mm nozzles should be able to print this without issues.

• For more unprecise / printers with bigger nozzels model files with 1.75 mm are available for download, too. Choose this variant if you cannot push the tape measure through the gaps.

Build notes:

• Push the tape measure parts through the 3D printed holders and center them carefully

• Put strips of heat-shrinking tube WITH glue over the fins to keep the tape measure in place

  

• Use superglue (and zip ties) to fix the printed elements on the boom. Check correct positions at least twice before glueing.

• Cover (at least the outer edges) of the tape measure by heat-shrinking tube WITHOUT glue

• Connect cable

• Have fun and share your results!

Links:

[1] https://www.draussenfuchs.de

[2] https://www.ikea.com/de/de/p/trixig-massband-90546911/

[3] https://github.com/draussenfuchs/draussenfuchs.de/raw/refs/heads/main/ant/draussenfuchs.de_ant_gerber.zip