Metering Out the Mini W3EDP

Last spring at one of our ham campouts (read about it here), I was surprised that the 21' tall Mini W3EDP antenna I was using worked so well on 80 meters.  By all rights, it just shouldn't have been that good.  To get a little more understanding of this thing, I took an hour last weekend to hang it from a limb (well clear of the trunk and everything else) and look at what it's doing with an SWR, resistance, & reactance meter.

Resistance as measured here is essentially radiation resistance, i.e., electrical energy being converted into radio waves, while reactance is (being non-technical here) push-back from the antenna that looks like resistance but that doesn't contribute to sending radio waves.  The whole situation's complex.  (joke! you laugh now!)  Will call them R and X for the rest of this post.

First though, a description of the antenna.  Inspired by a design at thewakesileave.com, I built a slightly more robust antenna.  It consists of a 16.75' piece of 22 gauge wire (anything similar will do) soldered to one side of a 3.5' piece of 450 ohm window line.  Wait, cut it a few inches longer and tie to an insulator at the top.  Suitable lugs were added to the other end of the window line, which attaches to a 4:1 balun.  Be sure to hook the antenna leg to the "hot" side of the balun, and the short ladder-line only leg to the ground side.  (I'm using this LDG voltage balun, though this similar current balun is probably a marginally better choice.  Same price.  If I had to do it over again...  But either should work.  Or roll your own, it'll work too.)  A length of coax cable attaches to that, which goes to your antenna tuner.  Yes, this design requires a tuner.  At least the rest of the antenna is cheap.  I'd show a picture, but it's kind of a mess visually, and this description is even better if you're building one.

In actual use so far, I've hung a 17' ground wire off the HF radio (or SWR meter here).  Might do better on the low bands to hang a 34' wire as well, and let the radio waves figure out which path they want to take.

Back to the antenna testing.  Hung it from a tree limb with the balun near ground level.  Used a stake to keep the bottom end from swaying in the breeze.  Swept through each of the HF and adjacent ham bands (160 & 6m), and tabulated the R and X at the bottom and top of each band.  Whenever there's a pair of numbers, it's for the bottom–top of band.  Results and notes:

• 160m was hopeless, with sky-high SWR and R; X however was 0.  huh.
• 80m was OK.  SWR in the 7-ish range, R from 270–31 ohms, X 121–61.  Not ideal, but OK.
• 60m was a little better.  SWR 3.0–2.8 , R 25–6, X 21–19.  It'll sorta work.
• 40m much better.  SWR 2.0–1.6, R 114–59 ohms, and X = 0 across band.
• 30m is good, SWR 2.0–2.1, R 114–59, X 0–27.  Could work (barely) without a tuner.
• 20m is weird but good.  SWR 4.2–4.6, R 300-ish ohms, X = 0.
• 17m is OK.  Such a narrow band, just took 3 numbers: SWR 6.9, R 337, X 92
• 15m is great: SWR 2.0–1.7, R 25-ish ohms, X = 0.  This at least partially explains how I made that one voice contact to Washington state last WFD on just 5 watts.
• 12m will tune, but it's meh: SWR 3.1-ish, R 65-ish, X 53-ish.
• 10m is a little better: SWR 2.4–4.7, R 286–145, X 73 across the band.
• 6m is OK for the low parts of the band: SWR 2.4–4.7, R 144–129, X 0–104

Not too surprisingly, CB will work here too (still need the tuner), with SWR in the 5-ish range and X fairly low.  That's a nice bonus, and I'll have to try it out on a future campout.

I've seen various suggestions to hang the ground wire off the ground leg lug at the balun, so I tried these too.  In general, they gave similar but lower SWR and X values.  I suspect it was just some RF getting damped out on the ground, a net loss of radiated power.  I'll be grounding a the radio.

Anyway, yeah, it works!  At 21' total length, it's easy to hang in a tree.  (How many times have we seen people spend hours trying to hang something wondrous and complicated at a remote campsite?)  It does require a tuner and decent coax, but it works fine at QRP power up to at least a full hundred watts.  Is it the perfect antenna?  No, but none are.  What is surprising is that it performs fairly well all the way down to 80 meters.  It's a good antenna to get started on (cheap! DIY!), and a great antenna to take camping.

So what is this thing?  It's a Zepp.  It's a heavily adapted version of the original W3EDP.  It's a mini-G5RV with the ground arm chopped off, then hung up vertically by the remainder.  I wouldn't even want to see what an antenna modeling program would make of this thing. But most of all, what it is is something that works.