The End Fed Half Wave antenna (EFHW)for SOTA portable operation…from bits and pieces in the Junkbox…
Whilst leisurely chasing activators this morning, I also took the opportunity to rummage through my Junkbox to see if I had all the bits and pieces to make an end fed half wave antenna for the 40M band. My main antenna for 40m at the home station is a Butternut HF2V, and is a good performer for SOTA chasing work, but I intend to activate a few summits in the near future, and although I’m well equipped for VHF, I need a good portable antenna for my planned activations.
I did a bit of research on the EFHW during the previous week, looking at what was written on the Internet about the antenna and what kits, if any, were available and at what cost. I found a few, but decided that the best way forward was to knock one up with the stuff I had on hand…
There’s not much to them, and the whole thing took me about 2 hours to assemble.
The VK5LA EFHW Tuner
Firstly, The circuit – There seemed to be a fair variation on the theme in terms of components used but ultimately, it’s just a tuned circuit set to resonate at the frequency of interest. Matching – some used link coupling of the tuned circuit, some with a tap up a few turns from the earthy end of the inductor. I went with this…
Hand drawn Circuit
Quite a few of the circuits used the Yellow toroid but I didn’t have one so I used a T50(Red) one that I had on hand. 24 Turns was about average for the schematics I gleaned and the tap 3 turns in from the earthy end seemed to be standard. The capacitor was one I had on hand that came from the board of a 70’s am transistor radio that was long ago junked.
Wiring diagram
I had a small black plastic Jiffy box on hand so I mounted everything in it and soldered it up as per the above diagram. The red banana plug socket on the side was added just in case if I need it for later. The black banana plug socket is for a counterpoise wire if desired. I found that I didn’t need one when testing, I think because I’m using a tap on the inductor L1. Dead simple!
A peek inside…
I then cut a 21.6 m length of light weight hook-up wire for the 40M band and attached a banana plug to one end and a lug to the other. I attached the lug end to the tip of my 9 meter high Squid Pole that I had set up in the front yard, and the other end to the Tuner and FT817 via a short BNC to PL259 lead set up on a table.
Table top portable…in the front yard!
To be perfectly honest, I wasn’t really expecting it to work, I plugged it in and turned the FT817 to the 40m band and selected LSB…the dial was down at the bottom of the band and to my surprise I heard a few stations as I tuned up to around 7.1 MHz. Well, “here goes nothing” I thought as I began to turn the variable cap on the tuner, all of a sudden the noise sharply increased and a smile emerged on my face! I knew then it was working and a brief “VK5LA testing” on a clear frequency allowed me to adjust the SWR to nothing on the Rig with the Variable capacitor at around 1/2 mesh…pretty well where it should be…
The complete EFHW 40M antenna packs down to a small package…
Now the acid test! did it work? could it make contact? It seems that it was certainly hearing ok, with a lively 40m band jumping out at me…I was about to find out as heard the bleat of my SOTAgoat alert on my iPad, letting me know that Alan, VK3HRA/P on VK3/VC-002 Mt Donna Buang was calling CQ on 7.103 MHz. I tuned to his frequency, and he was a good signal, very readable at 56…To my delight, Alan came back with a 58 for me for my first EFHW contact.
I’m certainly impressed by the EFHW antenna, and I’m looking forward to giving it a run out on a summit in the very near future…in the mean time, I’ll try different configurations like an inverted L and V, and perhaps as a vertical, to see how it goes. I might even adapt it by making the wire “linkable” for 10/15/20/40 like the Link Dipole that others swear by.
Experimenting is the essence of Ham Radio!!!
Andy – VK5LA
VK5LA - Andy's Amateur Radio Adventures... 