A reader of my recent article Sontheimer coupler – transformer issues and the follow up articles giving better transformer designs asked whether the coupler use in the popular AT-100 ATU wouldn’t be a good solution. A quick Google search did not turn up any published design rationale or measurement data for the AT-100 coupler design. … Continue reading AT-100 ATU Sontheimer coupler using a single binocular ferrite core
At Ferrite cored RF chokes in Class-E RF power amplifiers a design was offered for a choke using a Fair-rite 2843000202 core (commonly sold as a BN43-202), and the point was made that some products sold as BN43-202 might be significantly different. Let’s look at the calibrated model estimates of choke impedance and core loss, … Continue reading Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues
Class-E RF power amplifiers have become quite fashionable in ham radio in the last decade or two. This article discusses a common issue with the design of the RF choke providing DC to the Class-E stage. Above is a circuit above is from (Sokal 2001) which explains the amplifier and gives guidance on selection of … Continue reading Ferrite cored RF chokes in Class-E RF power amplifiers
This article documents estimation of common mode choke impedance by three different measurement techniques. The test uses a small test inductor, 6t on a BN43-202 binocular core and a small test board, everything designed to minimum parasitics. This inductor has quite similar common mode impedance to good antenna common mode chokes. Above is the SDR-KITS … Continue reading NanoVNA-H4 – a ferrite cored test inductor impedance measurement – s11 reflection vs s21 series vs s21 pi
By broadband transformer, I mean a transformer intended to have nearly nominal impedance transformation over a wide frequency range. That objective might be stated as a given InsertionVSWR over a given frequency range for a stated impedance. eg InsertionVSWR<2 from 3-30MHz with 3200(+j0)Ω load. These are used in many things, including medium to high power … Continue reading On ferrite cored RF broadband transformers and leakage inductance
One often sees people ask for help in choosing a ferrite mix for a particular application. A recent thread on social media asks for help designing a unun for the 1.8MHz amateur band, and it has provided the opportunity for participation, even if the content was not good. An important early step in designing a … Continue reading Choosing a ferrite mix for a 160m unun rationally
EFHW-2843009902-43-2020-3-6kThis article applies the Simsmith model described at A simple Simsmith model for exploration of a common EFHW transformer design – 2t:14t to a ferrite cored 50Ω:200Ω transformer. This article models the transformer on a nominal load, being . Keep in mind that common applications of a 50Ω:200Ω transformer are not to 200Ω transformer loads, … Continue reading A simple Simsmith model for exploration of a 50Ω:200Ω transformer using a 2843009902 (BN43-7051) binocular ferrite core
In a recent online thread, a ‘new’ online calculator was touted: https://miguelvaca.github.io/vk3cpu/toroid.html . References without any qualification surely imply a recommendation. In the same thread, Roger Need compared his measurement of a FT50-43 with Calculate ferrite cored inductor (from Al) (one of a set of related calculators), and Ferrite permeability interpolations. Above, his calculation reconciles … Continue reading Yet another ferrite toroid calculator – but is it any good?
One of the magic ham recipes often proposed is to stack two ferrite cores of different permeability for an RF inductor, but an explanation is rarely offered, I have not seen one. An explanation Starting with some basic magnetism… The inductance of an inductor is given by . For a closed magnetic circuit of high … Continue reading Stacking two ferrite cores of different permeability for an RF inductor
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