An end fed half wave antenna for RaDAR

I finally decided to try an End Fed Half Wave Antenna (EFHWA) and was pleasantly surprised!

Just before 14:00 on Saturday 14th of July 2012, I heard Barrie ZS6AJY, first present on the CW Net, frequency, 7020 kHz CW. I called him at 2.5 Watts working into the 20.5m long EFHWA in Inverted Vee form, the middle hoisted into a tree. No radials (Except the short coax and FT817ND were lying on the ground). Barrie heard me! He gave me a report of RST 579! Just before I said goodbye (Running on long last charged rechargeable penlight batteries) I went to the lowest power setting (Around 500 mW) and Barrie said signals were much the same! I think this proves, beyond any doubt, that the EFHWA does work with a simple impedance matching network at the feedpoint. AWESOME!!! The RaDAR “One contact per kilometer moved” (Single band 40m) can now become a reality!

For details on this antenna, see http://www.earchi.org/92011endfedfiles/Endfed40.pdf

I built my matching network into a small conduit box. I had stripped a 4:1 balun for the hardware and was OK with the idea having a spare 4:1 balun. In fact the conduit box was part of this excellent balun built by Dirk, ZS1X. I had no toroid in my junk box and this was the only logical way to go. The coax capacitor (See the article) was made from RG58cu, a little more bulky but served the purpose well. I mounted the conduit box onto a light chopping board. As can be seen in the picture, the chopping board serves the purpose of winding up the 20.5m wire too. Note the vee’s cut into both sides of the board. I use cable ties to hold the tent pegs in place too so they don’t get lost in transit (Or cause rattles). All antenna hardware in one place! There is a mod to be done, not seen in the picture but replacing the tent pegs with flourescent plastic green ones which is ideal for night time operations in the field. The chances of loosing a tent peg are much reduced. It’s not safe to loose these items in the field anyway.

The antenna itself can take on many forms. Inverted vee, inverted L or simply as a sloper, the far end tied to a high point. These various configurations would have an effect on the radiation angle. Certainly, this antenna performs well as an NVIS antenna!

I normally carry a length or two of nylon rope to string the antenna to a high tree branch or similar. I normally look for a reasonable sized rock and tie it to one end. Using the “Underarm” method, it’s easy to then get the rope up and over a tree branch with reasonable accuracy. Depending on how cluttered the branch is with sticky smaller branches determines the size of the rock. It has to fall through on the way down!

Although the EFHWA does not require a counterpoise (In effect, the short coax feed and radio are a conterpoise), getting the antenna into a tree may require a counterweight!

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