I have written several articles on design of high ratio ferrite cored transformers for EFHW antennas. Having selected a candidate core, the main questions need to be answered: how many turns are sufficient for acceptable InsertionVSWR at low frequencies and core loss; and what value of shunt capacitance best compensates the effect of leakage inductance … Continue reading A Smith chart view of EFHW transformer compensation
The article End Fed Half Wave matching transformer – 80-20m laid out a design for a EFHW transformer based on the readily available FT240-43. This article builds an NEC model for an EFHW antenna at 3.6MHz incorporating a realistic model of the above transformer. NEC provides for a NT card characterising a two port network … Continue reading FT240-43 matching transformer for an EFHW – NEC model at 3.6MHz
The article Small efficient matching transformer for an EFHW laid out a design for a small EFHW transformer. This article builds an NEC model for an EFHW antenna at 3.6MHz incorporating a realistic model of the above transformer. NEC provides for a NT card characterising a two port network using Y parameters. Y parameter model … Continue reading Small efficient matching transformer for an EFHW – NEC model at 3.6MHz
EFHW exploration – Part 1: basic EFHW explored the basic half wave dipole driven by an integral source as a means of understanding that component of a bigger antenna system. The EFHW can be deployed in a miriad of topologies, this article goes on to explore three popular practical means of feeding such a dipole. … Continue reading EFHW exploration – Part 2: practical examples of EFHW
The so-called End Fed Half Wave (EFHW) has become very fashionable amongst hams. The idea of end feeding a half wave antenna is hardly new, and there is widespread use of the broad concept… but from online ham discussion, it can be observed that the things are not well understood and indeed, there is magic … Continue reading EFHW exploration – Part 1: basic EFHW
At PD7MAA’s BN43-202 matching transformer for an EFHW I gave an estimate of the core loss in PD7MAA’s transformer. An online expert questioned the analysis and later measurements, and proposed his own transformer design as evidence. Notably, his transformer uses #61 material and a larger binocular core, a Fair-rite 2861006802 with 2t for a nominal … Continue reading WW1WW’s matching transformer for an EFHW
At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. I have been offered input VSWR curves for such a configuration, … Continue reading Small efficient matching transformer for an EFHW
A published design for an EFHW matching device from 80-10m uses the following circuit. Like almost all such ‘designs’, they are published without supporting measurements or simulations. The transformer is intended to be used with a load such that the input impedance Zin is approximately 50+j0Ω, Gin=0.02S. Analysis of a simple model of the transformer … Continue reading FT82-43 matching transformer for an EFHW
The net abounds with articles on broadband transformers (ie untuned) for matching End Fed Half Wave (EFHW) antennas to 50Ω. One of the aspects that is common to most designs is that the turns of the primary winding are wound ‘bifilar’ with the start of the secondary winding, indeed the twist pitch is often very … Continue reading On winding configuration of EFHW matching transformers
Ellington describes in a Youtube video his high power matching transformer for an EFHW, he rates it suited to 500W CW. Like almost all such ‘designs’, they are published without supporting measurements or simulations. The transformer is intended to be used with a load such that the input impedance Zin is approximately 50+j0Ω, Gin=0.02S. Analysis … Continue reading Ellington 3 x FT240-52 matching transformer for an EFHW