Working portable, I have been using my old and trusty commercially made W3DZZ. Indeed, it has been serving me nicely over the years. Being basically a dipole it has been performing as one could expect a dipole would perform. No more, no less, no problems, no complaints. For portable activity it´s, however, a bit heavy and cumbersome. The traps are heavy as is the balun, the wire is meant for permanent istallation and thus sturdy and it needs a coax (RG-58) which add weight to what you have to carry around. Something more nimble and more lighter with about the same performance would be nice.

The portable operations I aim for is primarily the Portabeltesten and some future SOTA activations. In both cases I need to be able to quickly switch between two bands; in the first case between 80 and 40 meter and in the latter case between 40 and 30 meters. A trapped end-fed half-wave dipole seems to be the ideal solution. Such an antenna/wire can be made very light and any coax is of course not needed.

The first task was to construct two traps; one for 30 meter and one for 40 meters. As I will be working at qrp-levels and as everything has to be as light as possible I made them of PVC-pipes 40 millimeter in diameter and from RG-174 coax. Instructions how to do you can find here. After quite a few attempts I ended up with 7,4 turns for the 30-meter trap (10.120 MHz) and with 10,25 turns for the 40 meter trap (7.020 MHz).

Each trap has to be tuned to the frequency you are aiming at. One can´t rely on some instructions specifying the number of turns. Even if you use RG-174, as I did, you can´t be certain it´s the same stock that I used. You have to tune them yourself! This is my way of implementing Marc´s suggestion how to tune a trap.

We are dealing with an end-fed half-wave dipole so you of course also need a tuner to match the high impedance at the end of the dipole to the 50 ohms of your tranceiver. As I need to quickly switch between two bands I have made a tuner with two variable capacitors and a switch. The tuner is based on the ideas of AA5TB.

The antenna in invertet-vee configuration supported by a 12 meter SpiderBeam Mast. It´s quick and easy to raise the mast with the wire attached. A whole lot easier than hoisting the old W3DZZ!

Of course you don´t have to buy a SpiderBeam Mast. The antenna is so light you can use any kind of resonably long fishing pole you can buy in your local shop for sport-fishing equipment.

On the lower band – 80 meters on the 40/80 meter antenna and 40 meters on the 30/40 meter antenna – the trap will act as an inductor and thus shorten the antenna/wire. A fraction of the transmitted power will be lost as heat in the trap, but the effect will hardly be noticeable. It´s just a matter of parts of an S-unite at the receiving station´s end. The advantage of having a shorter and easier to erect antenna far outweighs the disadvantages