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
QST publishes a design by W0SJ for a nominal 50:450Ω EFLW matching device from 160-10m using the following circuit. The article is ‘in-brief’ as technical stuff that will not interest most hams is published privately on a members-only page. This article is based on the information in the QST article alone (ie not on the … Continue reading W0SJ matching transformer for an EFLW (Laird 28B1540-000)
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
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
End Fed Half Waves have certainly captured the minds of QRP aficionados, and there is a steady stream of ‘designs’ appearing on the ‘net. A recent article by PD7MAA describes such a transformer using a BN43-202 balun core for up to 20W PEP from 7-29MHz. Above is PD7MAA’s graphic for his transformer. It is a … Continue reading PD7MAA’s BN43-202 matching transformer for an EFHW
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
A correspondent having read End fed matching – design review raised a similar design by PA3HHO which uses a#43 ferrite toroid as part of an end-fed matcher, see Multi band end-fed (English). Further to End fed matching – PA3HHO design review , this article has a solution to PA3HHO’s “original 40/20/10 version” using FT140-43 with … Continue reading End fed matching – PA3HHO design review #2
Measuring an RF inductor This article walks through practical measurement of a ferrite toroidal inductor using an antenna analyser. To be relevant practically, lets use an example from N4SPP’s end fed wire antenna on 3.6MHz. His coupling transformer uses a two turn winding on an FT240-43 core for the nominal 50Ω connection to the antenna … Continue reading Exploiting your antenna analyser #10