Saturday, May 14, 2011

My Favorite Cheap HF Antenna, The W3EDP

station
The station, my "Killer Watt" SW-40, Emtech ZM-2 Tuner, and W3EDP antenna, ready to play!

There's a good bit of info on the interwebs about the W3EDP:


Here's what it looks like (kinda) - but the info's a little off.
Here's some good info, but no pictures
A slew of experiences from a popular ham radio forum
Another Blog article, looks like he may have done some modeling of the antenna too!
I call mine the improved W3EDP because of some theory that I learned about end fed antennas in general, and about the W3EDP in particular.

Some time ago, on QRP-L, there was a great post about the W3EDP By W6JJZ
It was epic in my understanding, especially this part:
To understand the W3EDP, instead conceive of the short side as
one side of a feedline that's been separated or pulled apart from
the other side of the feedline.

Now in your mind move the short side so that it's parallel to the
first 17 feet of the long side and anywhere from several inches
to a foot or so away. What you have is a section of feedline.

I added the emphasis.
A W3EDP is an end-fed zep! Well, I guess you should say that a classic W3EDP is a pragmatic zep, because the matching section of line goes wherever you want, as a mislabeled "counterpoise."
To improve the design, I made a W3EDP antenna in Zepp formation. I took some 450 ohm ladder line (Wireman #553) and used it for the first part of the 85' wire, and all of the 17' wire, adjusting for velocity factor. Then I took 68' (85-17) of "Silky" antenna wire (Wireman #523) and attached it to one side of the ladder line. I put a red banana plug on the 'long' side, and a black one on the 'short' side.

closeup
The banana plugs, notice that I've added some string through the solid parts of the insulation for stress relief.

I used buttons for insulators.
far_end
you can see the button on the end, it's from old army surplus pants. They make the best insulators because they are durable, unobtrusively colored, and suitable for modification (you can make the holes bigger with a pocket knife)

When rolled up, the antenna is compact and easy to store
W3EDP_ready
Ready to store.

boxedup
in the box!
It goes anywhere!

That's my account of this wonderful antenna, I hope you can build one. I've used this one to talk to people all over the place. The silky wire means it bends well without kinking, you can also get good result with speakerwire, but using speakerwire means you will have to tear the wires apart. You could just make two at once, and give one to a friend!

HV FN ES 73!
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