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.
- 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.
Extract of VK1AD SOTA Activator Log – Mt Cowangerong 28 February 2021. Radio FT817ND output power set at 5 watts.
|00:03||VK5IS||14MHz||SSB||Ian s59 r57|
|00:04||VK1MA||14MHz||SSB||Matt s59 r43|
|00:06||VK1MIC||14MHz||SSB||Wade s51 r55|
|00:08||VK4CZ||14MHz||SSB||Scott s59 r56|
|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|
|00:28||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|
Standby for an update in the next week. I will update this post with VSWR plots.
Last Update: 11April 2021