A big congratulations to Gabriel who sat the test today at MP. Having easily passed and quickly submitted the required paperwork, he is now the proud holder of ZL3LOL !
Martyn has made a QRP balun for an endfed, so with the weather being perfect for outdoors antenna testing, we interrupted the coffee drinking to test said balun out. A length of wire, a bit shy of ½ λ on 40m was strung out at a low level between trees. Initially, no “short side” to the dipole was added ( I hate the term counterpoise – ED ), with the coax braid expected to provide the “other side” of the antenna. On Martyn’s NanoVNA, a dip showed around the second harmonic, but no fundamental was evident. A ferrite toroid was found ( how convenient ), and 12 turns of the coax feedline wound through it, placing it right up close to the 1:49 transformer for the endfed. A wire of around 1.9m was attached to make up the “short side” of the near endfed (NEF?) and magically, the fundamental resonance made itself known.
Frequency was a little high, so the long side of the antenna was extended. This bought 40m within range. 20m was a little high – this is a common problem, in that higher frequency “harmonics” tend to resonate above the mathematical harmonic frequency, and therefore put them slightly out of the desired spot. Interestingly, the change in resonant frequency with height changes, affected the high frequency more. Creating a small loading coil in the long side of the dipole, will affect the higher frequency more than the lower, and therefore can be used to bring both frequencies into the desired working area – an experiment for another day.