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
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
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 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
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
This article describes a Guanella 1:1 current balun which has high common mode impedance (Zcm) and low Insertion VSWR. It is for application on antennas that have low VSWR50 on at least some bands, especially if they would be used without an ATU on some bands. The purpose of the balun is to minimise common … Continue reading A low Insertion VSWR high Zcm Guanella 1:1 balun for HF
My article G3LNP balun explored the operation of the G3LNP 4:1 balun on a 200Ω asymmetric load and found it exhibited extreme Insertion VSWR on what should have been an ideal impedance transformation but for the asymmetric element. The balun is in fact a Voltage Balun and cannot be expected to work properly on asymmetric … Continue reading G3LNP balun with symmetric ‘matched’ load
A reader of A Demagnetisation Risk Index for a sensorless brushless DC drive asked whether the inductance of a sensorless brushless DC motor could be measured with one of the inexpensive LC meters available on eBay. Motor inductance line-line typically ranges from several µH up towards 100µH. Importantly, the fundamental frequency of flux change in … Continue reading Inductance of sensorless brushless DC motors
Walt Maxwell (W2DU) described a simple common mode choke or 1:1 current balun using ferrite sleeves slipped over a coaxial cable. Maxwell gives the choking impedance of two of his recommended chokes in Fig 21-3 from (Maxwell 2001). He does not give any detail of how he arrived at the curves, and in correspondence declined … Continue reading Common mode impedance of W2DU baluns
I have written some recent articles about or relevant to PD7MAA’s BN43-202 EFHW matching transformer. At about the same time a discussion started on and through that discussion, one ‘online extra expert’ stated that my analysis was bogus (dictionary meaning: not genuine, faked, a misrepresentation). This article presents detail that was not included in the … Continue reading PD7MAA’s BN43-202 matching transformer for an EFHW – full measurement set