The j value

I have noticed growing use of new lingo for reactance on hammy online forums… the term j value is replacing Reactance in the ham vernacular (though of course j does not distinguish Reactance from Susceptance). A well-designed ferrite transformer operated in the HF spectrum is close to ideal, so if it steps R by 2, … Continue reading The j value

nanoVNA – evaluation of a voltage balun – RAK BL-50A

In this article, I will outline an evaluation of a ‘classic’ voltage balun, the 1:1 RAK BL-50A voltage balun, specified for 1.8-30MHz. These were very popular at one time, but good voltage baluns achieve good current balance ONLY on very symmetric loads and so are not well suited to most wire antennas. Above is a … Continue reading nanoVNA – evaluation of a voltage balun – RAK BL-50A

Measurement of recent ‘FT240-43’ core parameters

This article reports measurement of two ‘FT240-43’ cores (actually Fair-rite 5943003801 ‘inductive’ toroids, ie not suppression product) purchased together around 2019, so quite likely from the same manufacturing batch. IIRC, the country of origin was given as China, it is so for product ordered today from element14. The measurements are of 1t on the core, … Continue reading Measurement of recent ‘FT240-43’ core parameters

A Smith chart view of EFHW transformer compensation

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

(How) does this balun work?

I was sent a pic of a balun and asked to explain how it works. With no other detail than the pic, it is difficult to supply a complete answer. Nevertheless, an analysis of what is presented follows. Last update: 6th November, 2020, 5:39 PM

SND implications of variations on the untuned small loop at MF/lowHF

Three recent articles developed an explanation of the YouLoop-2T at MF/lowHF: Small untuned loop for receiving – simple model with transformer ; A transmission line 1:4 impedance transformer ; and Towards understanding the YouLoop-2T at MF/lowHF . The first and third articles explained the concept of signal/noise degradation (SND) statistic, and gave graphs of the … Continue reading SND implications of variations on the untuned small loop at MF/lowHF

WIA 4:1 current balun – further measurements

I mentioned in my article WIA 4:1 current balun that the use of a single toroidal core in the above graphic compromises the balun. This article presents some simple measurements and analysis that question whether the balun works as so many users think. The popularity of the balun derives from the work of VK2DQ and … Continue reading WIA 4:1 current balun – further measurements

4:1 current balun – identifying bad ones

Correspondents have informed me that the balun dealt with in article 4:1 current balun – review and fix and variants are very common. This article gives a checklist of common issues and some basic measurements using an antenna analyser that should reveal some issues without breaking into a sealed assembly. Introduction Baluns are commonly employed … Continue reading 4:1 current balun – identifying bad ones