My antenna…
If you have read any of my previous amateur radio related posts you may by now be well aware that I don’t have the best of antennas.
To be perfectly honest it’s a bit difficult to gauge just how much of that is mere perception due to relatively poor conditions these past 12 months but, compared to more efficient resonant wire antennas or exotic beams, my end fed wire is at best what they call a ‘compromise’ design.
This antenna is known variously as the ‘no counterpoise antenna’ or an ‘end fed Zepp’ - it is physically a long wire radiating element fed with a balanced feed line. It is usually constructed from either a 50ft or 25ft length of twin feed line (bell wire or speaker wire can also be used) where one of the wires is cut at the mid point and removed. The longer wire forms the radiating element and the remaining twin lead is the balanced feed line. My current installation employs a raditor of some 40ft with a 20ft feed line (having been sized to fit into the limited space available).
In this configuration it is an unbalanced antenna fed with a balanced feedline which results in the feedline also radiating. The most interesting property of this design however is the radiation pattern: For all frequencies that the antenna will load up on, the distributed current maximum stays at or near the center of the antenna where the twin lead stops and the single conductor (radiator) continues. This gives the antenna a radiation pattern very similar to that of a resonant half wave dipole, except that unlike a half wave dipole antenna being used as multi band antenna, the radiation pattern and current distribution remains intact over the full range of frequencies tunable for the antenna! This means nice low angle radiation with decent gain over a broad range of frequencies (using a tuner) without having to adjust the antenna length. Well so says the theory at least!
As you can see - on the face of it, according to the theory, this should be a good multiband, compromise antenna. It has the additional benefit of being end fed which for my setup is the only option when it comes to feeding an antenna. However, I will be reserving judgement for now because I am still not entirely convinced that it is working as well as the theory suggests it should.