Antenna Project – Rabbit Ears 2el 2m Telescopic Yagi

Saturday 23 November 2019 – I had planned to participate in the WIA VHF-UHF field day, however the forecast temperature is 33 degrees C (hot) and we have a thick red dust haze (hot northerly winds blow red dust from central Australia) which isn’t good for the respiratory system. So the plan for today is to construct a lightweight PVC hand-held telescopic 2 element 2m (145 MHz) yagi using two pairs of TV rabbit ear antennas as the driven and reflector elements. Approximate directional gain is 5dB.

Materials

• 1 metre length of 21.6 mm PVC water pipe, inside diameter is 18 mm (cut to length later). You can use a variety of lightweight materials for the boom.
• 1 * Plastic end cap – boom end cap at the handle end
• 1 * 1 metre length of RG58AU/CU Mil Spec coax – trim later
• 2 * telescopic TV rabbit ear antennas 80cm long (31.5 inches) online purchase
• 4 * solder tabs
• 1 * short length of solid copper wire
• 2 * M3 20 mm screws, nuts and washers
• 2 * M4 35 mm screws, nuts and toothed washers
• 1 * 50 ohm 4 hole BNC chassis socket and a solder tab
• 2 * M3 10 mm screws, nuts and flat washers
• 1 * 55 mm length of 20mm x 3mm aluminium bar
• 5 * cable ties
• 1 * 510 mm x 6mm dowel

2el 2m yagi dimensions @ 145 MHz. Start with the following dimensions and adjust the length of the telescopic elements evenly for a low VSWR.

Metric dimensions

Imperial dimensions

2 element 2m yagi antenna in the extended position, element spacing is 406 mm (16 inches) 0.2 wavelength (λ).

2el 2m yagi – top view

2el 2m yagi – underneath view

Telescopic driven element – top view

Driven element – underneath view. RG58AU/CU coax is soldered directly to the solder tabs.

Feed point – mounted in a cut out section of the 21 mm PVC pipe. The driven element is secured to the boom using a M4 * 35 mm long machine screw.

Reflector element – two elements are joined by two solder tabs and a short length of copper wire to form a continuous element.

Reflector element – mounted in a cut out section of the 21mm PVC pipe. The plastic mount is secured to the boom using a M4 mm * 35 mm long machine screw.

2el 2m yagi – elements in the collapsed position, next is the BNC socket mount

BNC socket mount – 20 mm x 3 mm aluminium bar bent to form an L-bracket

BNC chassis mount and aluminium L-bracket

BNC socket mount assembly

BNC socket secured to the boom at the reflector end – pass the M4 screw through the reflector mount and the aluminium L-bracket.

RG58AU/CU Mil Spec coax soldered to the BNC panel mount

Adjust the driven element length for your favourite 2m frequency. I plan to set my version to 145 MHz midway between 144 and 146 MHz.

Example: VSWR @ 146 MHz

VSWR – 146 MHz @ 4 MHz wide

Adjusted for 145 MHz – make the driven element a slightly longer on each side

VSWR – 145 MHz @ 4 MHz wide

With the operating frequency set, fold back the driven elements and mark the boom at the tip of the telescopic elements with a permanent marker. You now have a permanent reference for the length of the driven element. (Update 27 November 2019) Next make up a 510 mm (20.07 inches) length of 6 mm (1/4 inch) dowel as a measuring stick for each half of the reflector elements. Measure from the center of the PVC pipe. When not in use, store the dowel inside the PVC pipe, don’t forget the end caps. 🙂

Using a permanent marker, mark the length of the driven element on the boom. 🙂

510 mm length of 6 mm dowel. You can also scribe a mark on the dowel to the length of the driven elements.

510 mm length of 6 mm dowel stored inside the PVC pipe

Hand-held 2el 2m yagi antenna complete. Boom length is 730 mm, you can adjust the length to your own requirements.

I plan to use this 2el 2m yagi antenna for 2m SOTA activations on 144.2 MHz SSB and 146.5 MHz FM simplex. 5 dB directional gain is approximately 3 times the input power.

Have fun constructing your own hand-held 2el 2m telescopic yagi antenna. Total weight is 250 grams (8.8 ounces).

Last update: 27 November 2019