I recently purchased a copy of W7EL's new EZNEC for Windows antenna modeling program and shortly after was hit with an urge to cut wire. I started playing with an old idea I had several years back on how to get the maximum gain with the minimum amount of wire. Rhombic antennas are wonderful for gain but I don't live on a farm; and so I always keep coming back to the Extended Double Zep design. A compact design that looks great on the PC is an EDZep wire with a parasitic reflector behind each of the two major power nodes. It is effectively two yagis phased side-by-side. This design would not fit in my yard with the supports I have available for the direction I want to aim it. A design with only one reflector would be feasible if I put it in the place of my wire yagi antenna. Also, I wondered if the imbalance to the feed line caused by having only one parasitic reflector would create a problem of RF interference in the digital ham shack.

Every thing looked good on paper, so down came the dual yagi antenna and up went the SUPER ZEP. The dimensions shown are for a 15 thru 20 Meter Super Zep. It is aimed at Western Europe from Oregon and 33 feet above the ground.
The driven element is a full sized 15 meter EDZep. A tuner (with balanced output) at the radio is used to match the feed line (open ladder or TV twin lead) from the center-fed wire. Drop the feed line down or away from the antenna at 90 degrees for as far as possible. Keep the feed line away from metal objects if possible. The line may be attached directly to the balanced line output posts of any tuner. CLICK for DETAIL If that is not possible, construct (or purchase) a 4:1 voltage balun and connect the step-up balanced side of the transformer to the twin lead and connect a short run of coax to the unbalanced side. (See construction notes on the NB6Zep antenna.) You connect the other end of the coax to the unbalanced output connector on the tuner. This technique is useful for bringing twin lead from the outside into the shack through a window or other entry. Make a loop at the balun transformer to keep rain out of the device. CLICK for DETAIL
The antenna tunes up nicely on 10, 12, 15, 17 and 20 meters. On 10 and 12 meters the antenna has gain but does not function as a beam due to the multiple lobes for these frequencies. For these frequencies, the major lobes are not perpendicular to the wire and adding a reflector would not be practical. On 17 meters the antenna functions as a double zep antenna with gain broadside to the wire. (A reflector could have been added for 17 meters, put that's another project...) It is important to line-up the reflector wire ends with one end or the other of the driven wire (as shown).

The performance so far has been exactly as predicted. (Modeled gain is based on a dipole at 1/2 wave above ground.) Switching from the NB6Zep to the Super Zep antenna is like turning on a light switch when it comes to signals from Europe on 15 and 20 meters! Contacts to W2 land from Oregon have been more difficult since replacing the wider beamed yagi wire. However, the DX signals over the pole are easy to find through the East Coast QRM. This is a good indication that the design is working as planned. There was no RFI detected in the shack by the slight imbalance in the feed line. I believe I now have achieved the ultimate gain antenna to Europe for my situation (until that urge to cut wire hits me again)...

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