Mark, the Ham Florida Man has been running a series of YouTube videos scorning the ever popular EFHW antenna. See his latest here. The basis of his concern is that the 49:1 transformer is inefficient, robbing power before it gets to the antenna. Probably true, no matter how much research Colin, MM0OPX, has put into making them more efficient.
Mark’s answer is a collaboration with an RF engineer in Belgium, Joeri Van Dooren, ON6URE, who writes about all sort of antennas that he sells through his own store. In particular, Mark suggests replacing EFHW antennas with End Fed Off Center Fed, EFOCF, antennas which use a 4:1 voltage balun, one with much lower losses than the 49:1. Mark is a very good spokesperson for Joeri, making all the right points. Interesting ideas that sound reasonable. Maybe I should try one?
My deployment options here in the HOA controlled Casa Easton Antenna Test Range are few. There are no tall trees on this property, and no tall vertical structures. The best I can, unobtrusively do is a telescopic mast about 20 ft (6 meters) tall. That’s one of the reasons I use an EFHW much of the time, in an inverted vee deployment. Using a 3 ft plastic fence post at each end and the mast in the middle and about 66 ft of wire, I can easily reach anything East of the Rocky mountains from Central Florida, and sometimes well beyond, with the 5w TR-45L, QMX or QMX+ (actually 3.8w out).
I like this antenna because I can effortlessly switch between 40m, 20m 15m and 10m with NO need for a tuner.
Can I get the same convenience and improved efficiency with an EFOCF?
Of the EFOCF antennas at Joeri’s store, the EFOC17 appears the best fit for my property. “Why the EFOC17 is the Better Choice for 40M to 10M Operation” makes all the sales points. Length of 17 meters fits. Band coverage 40m – 10m fits. Sounds great. Let’s build one. Yes, as you know, I prefer to build when I can. The sales page for the EFOC17 has enough details for construction. I already had a good 4:1 voltage balun and plenty of wire. A group of clamp-on ferrite bead chokes arrived after a few days. It didn’t take long to assemble and deploy.
I deployed just as I do my EFHW, this time with the 3.7m coax counterpoise laying on the ground.
A VNA sweep from 3Mhz to 30Mhz shows 4 resonance dips, NONE of them on the CW parts of ham bands I prefer (40m, 20m, 15m, 10m) let alone the ones mentioned in Joeri’s articles. Further, checking the individual bands I use, I found SWR measures, impedances and reactance well beyond the tolerance of my rigs and most well beyond being tunable with my Four State QRP tuner.
I captured VNA charts for individual bands, but will save the bandwidth of posting them here. A summary of the 4 bands I really want show the following SWR levels and only 2 will work with my radios without needing a tuner. Definitely not a useable antenna for my needs.
40m, 7.040 Mhz, 6.715:1
20m, 14.060 Mhz, 3.504:1
15m, 21.060 Mhz, 1.937:1
10m, 28.060 Mhz, 1.585:1
Noting that Joeri says “Antennas mounted higher or lower than 10 meters may exhibit different SWR values.” I tried a different deployment. An older (broken 4 times) mast was good for 4 about meters height. I hoisted the balun and coax on that mast, getting all 3.7m of choked coax off the ground, and ran the wire as a sloper to the 6m mast 17m away. While less than half way to 10m, it was much higher than the inverted vee.
The results were not much different. Note well the lack of anything near 20m, my most used band.
Unresolved question:
I can’t really expect Joeri to answer this question since I’m not using an antenna I purchased from him, only one that I think is similar to his.
Does this antenna really need to be 10m high (impossible here), or did I make some other blunder building it?
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