This article describes a small matching transformer built and measured by Luis, CT2FZI, using a Fair-rite 2643251002. Above is the transformer with 100pF compensation capacitor across the input, and two resistors to make up a 3300Ω load in combination with the VNA port. Last update: 10th June, 2021, 5:16 PM
A chap recently posted some advice on construction of a dual ratio transformer for EFFHW antennas, advice with an informative pic, but without measurement evidence that it works well. Pictured is a dual UnUn. I made this for experimenting. It’s both a 49 and 64 to 1 UnUn. The 49 to 1 tap uses the … Continue reading Shorting winding sections of a ferrite cored EFHW transformer
This article offers a simple Simsmith model for the Small efficient matching transformer for an EFHW. Above is the model topology. D1 is a daemon block which essentially, calculates key values for the other blocks based on exposed parameters and the named ferrite material complex permeability data file. The prototype used a Fair-rite 2643625002 (#43) … Continue reading Small efficient matching transformer for an EFHW – a Simsmith model
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