A review of transformer design 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 is uniform, and the effects of distributed capacitance are insignificant. Above is a commonly used low frequency equivalent … Continue reading RF transformer design with ferrite cores – initial steps
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
Commercial products often have power ratings that bear checking. There are common some key properties that are relevant: where loss is high, core loss tends to dominate; the specific heat of ferrite is typically quite high; the capacity to dissipate heat is related to many factors. Last update: 14th April, 2024, 1:36 PM
The article Estimating the magnetising or core loss in a ferrite cored RF transformer discussed a first cut approach to determining the minimum magnetising impedance from a core loss viewpoint. This article considers the effect of magnetising impedance on VSWR. For medium to high µ cored RF transformers, flux leakage should be fairly low and … Continue reading Estimating the Insertion VSWR in a ferrite cored RF transformer
The article End fed matching – design review and many later ones set out a method of estimating the magnetising or core loss in a ferrite cored RF transformer (such as often used with EFHW antennas). There are two elements that are critical to efficient near ideal impedance transformation over a wide frequency range, low … Continue reading Estimating the magnetising or core loss in a ferrite cored RF transformer
A prototype broadband transformer for a End Fed Half Wave operated at fundamental and first, second, and third harmonic is presented. The transformer comprises a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to … Continue reading End Fed Half Wave matching transformer – 80-20m
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
The popular End Fed Half Wave is all things to all men, but this article compares an End Fed Half Wave, Inverted L, and Half Wave Dipole with some common parameters: frequency: 7.1MHz; flat top length: 20m; Height above ‘average’ ground (σ=0.005, εr=13): 10m; lossless balun / matching device. Key differences: ground connection: Inverted L … Continue reading End Fed Half Wave / Inverted L / Half Wave Dipole
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