SOTA – Lightweight Portable 2m – 70cm Dipole Antenna

Antenna Construction Project

Lightweight portable QRP 2m & 70cm half wave dipole for SOTA or an emergency antenna for the 2m and 70cm Go-box.

Parts:

• Section of nylon kitchen cutting board 50 x 30 mm x 7 mm (2 inch x 1 1/8 inch x 1/4 inch)
• 2 x 495 mm 6 section telescopic antennas with M3 holes,
• 2 x M3 screws 15 mm long with nuts
• 3 x solder tabs
• BNC panel socket with M3 holes
• 2 x M3 screws 10 mm long
• Balun – Toroid core T37-0 Tan (100 to 300 MHz) or T37-17 Blue/Yellow (20 to 200 MHz)
• Copper wire – 6 bifilar turns of  0.72 mm (21 AWG) winding wire

2m 146 MHz Portable Dipole Antenna Parts

Center insulator can be mounted over a telescopic pole, on camera tripod or hang it from a tree branch.Balun T1 toroid – T37-0  6 bifilar turns of 21 AWG copper wire (ignore the five turns shown in the diagram)

Toroid balun diagram not to scale

2m portable antenna collapsed length 280 mm (11 inches)

For operation on 144 to 148 MHz, extend each telescopic element to its full length 495 mm (19.5 inches). Center frequency is 146.5 MHz.

Lightweight 2m 146 MHz portable half wave antenna

Center insulator assembly

BALUN – Balanced to Unbalance

BNC socket and balun

VSWR scans with the horizontal antenna 2 metres above ground level. Feedline for the test is LMR195.

VSWR scan at 146.5 MHz, 4 MHz wide

VSWR scan at 146.5 MHz, 2 MHz wide

At 432 MHz the extended antenna is 3/4 wave length (3rd harmonic)

Antenna extended to full length – VSWR scan at 432.5 MHz, 2 MHz wide

Bottom view – Folded for storage in a small container – 110 mm x 70 mm (2 3/4 x 4 3/4 inches).

Top view

Last update: 25 June 2019

 

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