After being asked to activate a particular park on the air, I was told that an end fed half wave antenna would work well for portable operations. So with that information I began researching how to build an EFHW for 40-10m. I’ve build single band dipoles for these frequencies, but I wasn’t sure about how to go about this.
The main part of this antenna is a 49:1 balun. It is a transformer that has a 7:1 turns ratio, and isn’t too tough to make. So follow me as I lead you on a photo journey of how I built my 40-10m EFHW.
Measuring to find the center for the SO-239. 
After drilling I used silicone to seal the holes for water tightness. 
I used copper for where the wires will be soldered into the box. 
This is the finished box part 1. The wing nut is where the antenna will attach.
I cut about 136 feet of wire for the antenna. This can be shortened later when it comes time to trim and tune the final product.
Winding the toroid was the next challenge. It wasn’t as difficult as I thought it would be. I followed Steve Ellington from Youtube. Two wraps with twisted wire and then 14 wraps with the long length wire. I used a drill and a vice to wind the two lengths of wire together. Watch Steve wind his transformer. He explains it much better than I can. Solder it into the junction box as shown in the image with a 100pF 15kV cap from tip to ground on the SO-239.
Testing this with my RigExpert AA-170 was a joyous occasion. I was quickly able to loop the end of the wire about 12 inches and zip tie the end together so I could string it up with paracord. 40m, 20m, and 15m were 1.7:1 SWR. 10m was 2.2:1 in the CW portion and 2:1 or below for the voice portion. I consider that a win!
PARTS LIST:
1 4” X 4” X 2” PVC Junction Box (LOWE’S)
1 500 Ft. roll 14 AWG Solid (LOWE’S)
A few feet of 15 AWG Magnet wire Remington p/n 15SNSP.125 (DIGI-KEY 2328-15SNSP.125-ND)
1 Ferrite Toroids / Ferrite Rings 43 Toroid 12.7mm 61mm
p/n 5943003801 (Digi-Key 1934-1592-ND)
1 100pF +/-10% Capacitor 15kVDC p/n HVCC153Y6P101MEAX (DIGI-KEY BC5419-ND)
1 SO239 chassis mount female connector (Amazon sells these)
Various stainless steel nuts, bolts & eye hook
