THE $4SPECIAL by Joe Tyburczy, W1GFH
THE $4
Sure, you can find "all-band wire antennas" for sale in the back pages
of Ham magazines costing $150 or more. But beware: Marconi spins in his
grave everytime a ham buys an aerial instead of building it!
Look, the plain and simple truth is that wire antennas for the HF bands
were intended to be hand-made and not store-bought. Untold generations
of intrepid Radio Hams have fashioned their own equipment out of spit
and baling wire. In this world of microprocessor controlled micro-rigs,
this may be your only chance to build something and actually see it work
on the air. Think about it.
Another bonus of "rolling your own" antenna is that it costs you next to
nothing. Don't be intimidated by SWR, either. Your rig will not blow up
and kill you. Most modern rigs will politely refuse to transmit into a
really bad match. A perfect 1:1 SWR is for sissies, anyway. All *real*
hams have conducted perfectly good QSO's at 3:1, and even 10:1 at some
time or another. Anyhow, I recommend a tuner. This, you can buy over the
counter with a clear conscience.
I am a big believer in balanced line vs. coax. The basic "W1GFH $4
SPECIAL" shown below is a variation of the type of exceptional skyhook
I've been using for years. I've tried the commercial 450-ohm ladder
line, but prefer 300-ohm TV twinlead, and the cheaper the better.Forget
all that crap about impedance, wavelength, and velocity factor. What you
really need to concentrate on is getting an interesting set of antenna
insulators.
Back during the disco era when I first got on the air, I got a pair of really cool antique pyrex antenna insulators from a flea market table in Derry, NH for 25 cents each. They looked like the kind Hiram Percy Maxim used in 1910, and seemed able to pull in exotic DX all by themselves. The other day I found out that Radio Shack wants $5 apiece for insulators made from some kind of white plastic crap. So I improvised my own by sawing up pieces of an acrylic adjusting rod from a discarded miniblind. I think Hiram would've been proud of me. The tuner was an MFJ-949C I got at a swap meet for $15 a long time ago and has connections for balanced lines on the back. A link-coupled balanced tuner arrangement like the Johnson Matchbox would be better, but use what you have. The idea is to get on the air with a decent signal for cheap, just like they did in the early days of ham radio! I had a 65ft. per leg version of this antenna working in Masssachusetts, and it'd tune up on all bands 80-10. At my Burbank, California QTH, I used a 35 ft. per leg version, and it tuned up on 40-10. By the way, you'll notice it's an inverted vee --- a real advantage if you don't have room for a full-on dipole in your yard. If you still don't have room, bend and angle the legs to fit the space you've got. Antennas gently bent into Z-shapes still work fine!THE MAGIC OF TWINLEAD The feedline comes straight in thru a window sash. The nice thing about the 300 ohm twinlead is that the small stuff only needs about 2" separation from metal objects in its path. (OK, so TV Twinlead won't take a kilowatt, but the 450 ohm stuff you can obtain at ham stores will. You just need to be more careful with routing it)
You can get a 4:1 balun to make the transition from the balanced line to a length of coax, so you can bring the coax into the house via a properly sealed-up feedthough hole to avoid winter drafts if you'd like. If you really want to get nutty, try using 110VAC lamp cord ("zip" cord) as a feedline. Yeah, it'll work as a crude balanced line, believe it or not. Impedance varies, but is usually "close enough" to work. Improvise. Experiment. Play. Take notes of what works and what doesn't. This is what ham radio is all about. Many of you will recognize this antenna as the venerable "double zepp" aerial, a variation of the "end-fed Zepp" -- the skyhook responsible for the dramatic Hindenberg tragedy in Lakehurst, NJ. It seems the blimp's radio op decided to work a little DX while waiting for landing clearance. He sent out a few CQ's. Unknown to him, the ladder line had twisted in the breeze, shorting the bare conductors. A brilliant spark flared up, and....well, that's another story altogether. To see an "end-fed Zepp" version of this antenna, click here. Alas, I never had the height to make this antenna perform the way it should. The one in Mass. was up 50 ft. and worked terrific DX. The one I have now is only up 30 ft. and gets average results. It won't outdo a yagi at 100 feet, but what will? And for $4....who can complain?!
ADDENDUM: November, 2002 Since writing this article, I've gotten a lot of questions. Many are curious about the end-fed Zepp. I suggest you go to L.Cebik's fine page on this subject for an explanation of the practicalities of such an antenna:
http://www.cebik.com/gup/gup12.html The other question deals with feedline lengths. Is there any 'ideal' length? Yes and no. Some feedline lengths will present an extremely high impedance to the tuner on certain bands. Each installation is different, but here are some rough guidelines that may help:
Start by trying a feedline listed in the lengths below. It may take some trimming or adding of feedline to work well on the range of bands you want to cover. The worst possible feedline lengths are shown in brackets:
If Ant is 120 ft per leg it will cover 160 thru 10 meters. Feedline of 40-70 or 150- 190 feet suggested. [Avoid lines around 120 or 240 ft]
If Ant is 65 ft per leg it will cover 80 thru 10 meters. Feedline of 25-40, 80-100 or 140-160 feet suggested. [Avoid lines around 60, 120, or 180 ft]
If Ant is 33 ft per leg it will cover 40 thru 10 meters. Feedline of 40-50, 70-80, 100-110 or 130-140 feet suggested. [Avoid 30, 60, 90, 120 ft]
