A correspondent asked whether I had a tool similar to An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03) to assist in the design of a ferrite cored Ruthroff 1:4 balun for HF. In fact, the problem is the same as the one discussed in the article above, and the … Continue reading A Simsmith model of a Ruthroff 1:4 voltage balun – 2843009902 (BN43-7051)
A very common design of a n:1 transformer for EFHW antennas uses a 2t primary on and FT240-43 (or even smaller) ferrite core. In a process of designing a transformer, we often start with an approximate low frequency equivalent circuit. “Low frequency” is a relative term, it means at frequencies where each winding current phase … Continue reading nanoVNA-H – measure equivalent core loss resistance
An online expert recently advised: …The spec for type 43 makes it clear that it should never be used for HF unun construction. It is specifically engineered with a complex permeability that makes the core lossy on most HF frequencies. Since an unun is not a TLT (transmission line transformer) but rather an autotransformer, a … Continue reading An online expert on the unsuitability of #43 for HF UNUNs
The so-called End Fed Half Wave antenna system has become more popular, particularly in the form of a broadband matching transformer in combination with a wire operated harmonically over perhaps three octaves (eg 7, 14, 21, 28MHz). The broadband transformer commonly uses a medium µ ferrite toroid core, and a turns ratio of around 8:1. … Continue reading End fed half wave matching – voltage rating of compensation capacitors
A correspondent asked about the use of a Jaycar LO1238 ferrite core in VK3IL’s EFHW matching unit for 40m and up. The LO1238 implementation would use 3t primary and 24t secondary on the core. If the transformer is simply used without an ATU between it and the radio, and we assume that the antenna system … Continue reading End fed matching – VK3IL design on LO1238
David, VK3IL posted EFHW matching unit in which he describes a ferrite cored transformer matching unit that is of a common / popular style. Above is David’s pic of his implementation. It is a FT140-43 toroid with 3 and 24t windings and note the 150pF capacitor in shunt with the coax connector. The popular belief … Continue reading End fed matching – analysis of VK3IL’s measurements