Antenna Project – HF QRP End Fed Half Wave

Homebrew HF EFHW antenna for low power SOTA, Parks and field day events. Using a 19.8 metre length of wire mounted as an inverted V, a non-resonant 6.8 metre counterpoise, this antenna is resonant in the 40/20/15/10m bands. At 19.8 metres long, the VSWR is less than 1.5:1 in the voice segments. If your primary operating mode is CW, you may wish to consider changing the length of the radiator. Note an antenna tuner (ATU) is not required for operation in 40/20/15/10m bands.

Materials:

• Winder/Insulator: 3 mm kitchen cutting board, purchased from a mainstream supermarket (hint, down down)
• Toroid: FT140-43 from Mini Kits S.A.
• Capacitor: 100pf silver mica rated at 500v
• Length of enamelled copper wire (select the appropriate wire size for your maximum operating power)
• 2 x S-clips
• 27m 22 AWG insulated copper wire. Select the appropriate wire for your operating power.
• BNC socket or an RF socket of your preferred choice
• 2 x crimp auto spade connectors
• 2 x small cable ties
• 2 x M4 20 mm stainless steel round head, hex screws
• 4 x M4 washers stainless steel
• 2 x M4 washers large
• 2 x M4 wing nuts
• 2 x M4 stainless steel nuts
• 2 x solder tabs
• 2 lengths of 2 mm hoochie cord
• Fabricate an end insulator: Use an old plastic coat hanger or use a section of the kitchen cutting board

49:1 Impedance Transformer – 2 turn Primary and 14 turn Secondary. Twist together the first two turns of the primary and secondary windings.

Cut a section of 3mm kitchen cutting board 165 mm x 100 mm. The two winding cut outs are 25 mm deep by 63 mm wide.

Drill 4 anchor holes with a stepped drill bit.

Secure the 49:1 toroid in place with two opposing cable ties

The BNC connector ground tab and the counterpoise wire tab are soldered together to form a common ground.

49:1 Impedance Transformer circuit diagram

Post update 10 October 2023 – I have changed the enamel wire to 18 AWG or 1 mm. The turns and impedance ratios remains as is. See this post.

Insulator/winder is 3 mm kitchen cutting board purchased from a local supermarket

Homebrew EFHW 49:1 Impedance Transformer for 40/20/15/10m bands using a FT140-43 toroid and 100 pf silver mica capacitor.

Antenna tie off using a S-clip. Radiator is a 19.8 meter length of plastic insulated 22 AWG copper wire.

Feedpoint – BNC socket and the anchor tie off using a S-clip, bottom right. Counterpoise wire bottom left.

Portable homebrew EFHW Antenna assembly

Portable homebrew EFHW Antenna assembly – Rear view

Homebrew inverted V portable EFHW antenna supported by a 7m telescopic pole – SOTA activation using 40m and 20m bands.

Extract of VK1AD SOTA Activator Log – Mt Cowangerong 28 February 2021. Radio FT817ND output power set at 5 watts.

28 Feb 21 VK1AD QSOs from Mt Cowangerong – Image courtesy of SOTA Maps

Time	Callsign	Band	Mode	Notes
00:03	VK5IS	14MHz	SSB	Ian s59 r57
00:04	VK1MA	14MHz	SSB	Matt s59 r43
00:05	ZL3QR	14MHz	SSB	s55 r55
00:06	VK1MIC	14MHz	SSB	Wade s51 r55
00:08	VK4CZ	14MHz	SSB	Scott s59 r56
00:10	VK4BXX	14MHz	SSB	s59 r54
00:14	VK5PAS	14MHz	SSB	Paul s59 r57
00:18	ZL2ATH/P	14MHz	SSB	Wynne s56 r58 S2S ZL1/WL-138
00:20	VK4KC	14MHz	SSB	Marty s59 r54
00:20	VK3PF	14MHz	SSB	Peter s55 r42
00:22	VK4SYD	14MHz	SSB	Rob s59 r57
00:24	VK4NH	14MHz	SSB	s59 r55
00:28	VK3KAI	7MHz	SSB	Peter s59 r58
00:28	VK2IO	7MHz	SSB	Gerard s59 r45
00:30	VK4EKA	7MHz	SSB	Dougal s58 r51
00:41	VK1MIC	144MHz	FM	Wade s51 r51

VK1AD SOTA Activator Log – Mt Cowangerong

Standby for an update in the next week. I will update this post with VSWR plots.

VSWR plot – 7 MHz to 28 MHz

Last Update: 10 October 2023