Small efficient 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

FT82-43 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

Is |s21| measurement of a common mode choke meaningful to antenna systems?

A common theme among online experts is to measure, or ask for measurement of a common mode choke connected between the centre conductor of a VNA’s tx and rx ports. That raises the question of whether |s21| with both ends shorted is meaningful, whether it in any useful way characterises the choke as a component … Continue reading Is |s21| measurement of a common mode choke meaningful to antenna systems?

An RF choke for a 1.8-30MHz coax power injector – LF1260 core

This article describes a prototype RF choke (RFC) for use in a power injector for 50Ω coax over range 1.8-30MHz. Power injector / extractors are often used to connect power and / or signalling on a shared common RF coax feed line to accessories such as remote antenna switches and ATUs. Design criteria are: Insertion … Continue reading An RF choke for a 1.8-30MHz coax power injector – LF1260 core

End Fed Half Wave matching transformer – 80-20m

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

End fed half wave matching – voltage rating of compensation capacitors

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

On winding configuration of EFHW matching transformers

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 3 x FT240-52 matching transformer for an EFHW

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

A low Insertion VSWR high Zcm Guanella 1:1 balun for HF – more detail

This article expands on the detail behind A low Insertion VSWR high Zcm Guanella 1:1 balun for HF. Choice of core Online experts all have a preferred core material, but there is a dearth of measurement data to show the difference in actual use. If someone recommends a particular core material and cannot provide measured … Continue reading A low Insertion VSWR high Zcm Guanella 1:1 balun for HF – more detail