From May 2002 QST © ARRL

By Steve Ford, WB8IMY

Loop antennas have always fasci-nated me. From a common-sensestandpoint they seem impossible.

I mean, how can you have a short circuitat the output of your transceiver and callit an antenna? I’d call it bright flash,smoke, and stream of obscenities.

But the magic we call radio is neverso straightforward. Yes, a loop antennais unquestionably a short circuit at theoutput of your radio—if your radio pro-duced dc. Radio frequency energy, how-ever, is ac and it views a loop quitedifferently. A loop represents an imped-ance load to RF. The impedance valuedepends on the size of the loop, the fre-quency of the RF and other factors, but itis most definitely not a short circuit.

The October 1998 QST carried an ar-ticle of mine titled “One Stealthy Wire”in which I used a remotely tuned antennacoupler to match my radio to a random-wire antenna supported by a lonely mapletree in my back yard. If artists and musi-cians can go through creative “periods”when their muses suddenly decide to speakin different tongues, so can amateurs. The

One Stealthy DeltaThis HF antenna keeps a low visual profile while attracting plenty ofattention on the air.

Figure 1—A diagram of the Stealthy Delta.

The SG-237 tunerhangs on a woodprivacy fence, justbehind the tree trunk.

Do you seean antenna inthis picture?

Probably not!

From May 2002 QST © ARRL

maple tree is still here and so am I, butI’ve abandoned my single-wire period andhave embarked on the year of the loop. Orto quote Daffy Duck in the memorablecartoon, “I swear, your honor, I will neverpaint a malicious mustache on a work ofart again… I’m doin’ beards now!”

The Problem Remains the SameLittle else has changed in four years.

I still exist on a house lot the size of apostage stamp. The local squirrels haveeasements written into my deed. I stillhave a wife who distrusts my every moveand despises every antenna I attempt tocreate. When I wonder aloud about whereI can erect my next abomination, her re-ply is “Cleveland.”

I asked Dean Straw, N6BV, our resi-dent ARRL antenna guru, how I couldimprove my situation. The exchange wentsomething like this…

Dean: Put up a tower and a tribandYagi antenna.

Me: Do these things come with di-vorce documents?

Dean: How about a 100-foot dipole50 feet above the ground?

Me: Supported by what two tastefullydesigned 50-foot objects?

Dean: How about a vertical loop sup-ported by your tree?

That’s when the sweatsock-filled-with-nickels-of-inspiration struck meupside the head. How about a loop notonly supported by the tree, but in the tree?

The Stealthy DeltaA delta loop gets its classy moniker

from the Greek alphabet, namely the let-ter delta, or ∆. My Stealthy Delta is avertical wire triangle fed directly in themiddle of its base (see Figure 1). Formultiband HF operation the idea is tomake the triangle as big as possible. Italso helps to keep the base of the triangleabout 7 feet or so off the ground.

For my application each side of the tri-angle is 40 feet in length. Remember thatthe wire is continuous; that’s why they callit a loop. Using our wood privacy fence tohide the bottom wire, I strung the loop out20 feet to an insulator, up into the tree (toan insulator suspended by a Nylon rope),

down to another insulator on the other sideof the tree and then finally back to whereI began. Was it a perfect triangle? No. Wasit good enough for Amateur Radio androck n’ roll? You bet.

And now that it was strung, how wouldI feed the Stealthy Delta? I would needan antenna tuner for multiband opera-tion—that much was clear. With the tunerindoors I could use 450-Ω ladder linebetween the tuner and the feed point ofthe antenna. In my case, however, the lad-der line would have to take a torturousroute to reach the Stealthy Delta. It wouldhave to careen through the air and directlyover my wife’s sacred hedges and rosebushes. That was unacceptable (to her,anyway). The alternative was to use asubstantial length of buried coax, but co-axial cable is much too lossy in the faceof the high SWRs that would exist be-tween the antenna and the tuner.

If the mountain will not come toMohamet, Mohamet must go to the moun-tain. Or putting it in a ham context, if theantenna will not come to the tuner with-out unacceptable feed line loss, the tunermust go to the antenna. Borrowing an ideafrom my “One Stealthy Wire” article, Iinvested in a new SG-237 remote auto-matic antenna tuner from SGC Inc(www.sgcworld.com). I installed the tunerat the feed point, hiding it behind the treetrunk, and ran direct-bury coax and apower cable all the way back to the sta-tion. I buried most of the wires, except fora short run up the side of the house andinto the guest bedroom window.

How Does it Work?The SG-237 is RF activated. You trans-

mit and it finds a low SWR within a fewseconds. That low SWR is achieved at theantenna. With the good-quality coax I usedbetween the tuner and my radio, feed lineloss was kept to a minimum (a little over 1dB on 6 meters and much less on lowerbands). With my Stealthy Delta the SGCtuner can find an acceptable match withan SWR less than 2:1 on any amateur fre-quency from 80 through 6 meters. If I haderected a somewhat larger loop, I probablycould have operated the antenna on 160meters as well.

The privacy fencealso acts as ananchor for one of thelegs of the StealthyDelta.

The direct-bury coax makes a discreetjaunt into the bedroom window.

In terms of performance, the StealthyDelta is definitely superior to my singlestealthy wire. Even on 80 meters, whereit is way too short, the loop surprised me.During a recent RTTY contest I madeseveral contacts into Europe on 80meters, which I’ve never done before onRTTY from home. On 40 through 10meters I consistently receive strong sig-nal reports. I worked the XRØX and TI9MDXpeditions on RTTY after just a fewcalls and even managed to get through thepileup to work the PWØT group on 15-meter SSTV. Not bad for a wire triangle.

And best of all, the Stealthy Delta isvery stealthy indeed. The tree camouflagesmost of the antenna. The photos that ac-company this article were shot in Marchwhen the tree was bare and yet the antennais very difficult to see. Just imagine howinvisible it is when the tree is in bloom.

Will I stick with the Stealthy Delta?Certainly...for now. I can’t beat the per-formance and convenience, but I’m sureI’ll eventually think of something thatwill. Some day my “loop period” willgive way to some other source of annoy-ance for my wife and child…

“I swear, honey, I will never erectanother diabolical delta…I’m doin’rhombics now!”

You can contact the author at ARRL Head-quarters, 225 Main St, Newington, CT06111; sford@arrl.org.