A reader of End Fed Half Wave matching transformer – 80-20m asked if a good transformer could be made with with a FT114-43 core. The original transformer above comprised 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 … Continue reading End Fed Half Wave matching transformer – 80-20m – LO1238 variant
A reader of End Fed Half Wave matching transformer – 80-20m asked if a better transformer could be made with a stack of 2 x FT240-43 cores and using half the turns. The original transformer above comprised a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used … Continue reading End Fed Half Wave matching transformer – 80-20m – 2xFT240-43 variant
Ferrite cored inductors and transformers saturate at relatively low magnetising force. #61 material example Lets work through an example of a FT50-61 core with 10t primary at 3.5MHz. Magnetic saturation is one limit on power handling capacity of such a transformer, and likely the most significant one for very low loss cores (#61 material losses … Continue reading RF transformer design with ferrite cores – saturation calcs
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
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
I have noted recently the increasing popularity of the so-called End Fed Half Wave antenna, though the term often includes harmonic operation of the antenna. It seems that at the heart of common ham understanding of this antenna system is that some kind of two terminal feed device creates a scenario with current on the … Continue reading The magic of the End Fed Half Wave antenna / EFHW
A reader of EFHW transformer measurement – how accurate does the load need to be? asked whether the discussion applies more generally, in particular to the loads used for calibration and measurement with a VNA. In this article, unless stated otherwise, reference to |s11| and ReturnLoss are to those quantities expressed in dB. Note that … Continue reading NanoVNA – how accurate does the LOAD need to be – part 1?