PD7MAA’s BN43-202 matching transformer for an EFHW – full measurement set

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

PD7MAA’s BN43-202 matching transformer for an EFHW – measurement of a prototype

At PD7MAA’s BN43-202 matching transformer for an EFHW I gave an estimate of the core loss in PD7MAA’s transformer. This article reports measurement of a prototype built to his design.   Above is PD7MAA’s graphic for his transformer. It is a little confusing as an 11t wind will start and finish with ends as the … Continue reading PD7MAA’s BN43-202 matching transformer for an EFHW – measurement of a prototype

PD7MAA’s BN43-202 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

The magic of End Fed Half Waves / EFHW

I have noted recently the increasing popularity of the so-called End Fed Half Wave antenna, though the term often includes harmonic operation of the antenna. It seems that at the heart of common ham understanding of this antenna system is that some kind of two terminal feed device creates a scenario with current on the … Continue reading The magic of End Fed Half Waves / EFHW

nanoVNA-H – measure equivalent core loss resistance

A very common design of a n:1 transformer for EFHW antennas uses a 2t primary on and FT240-43 (or even smaller) ferrite core. In a process of designing a transformer, we often start with an approximate low frequency equivalent circuit. “Low frequency” is a relative term, it means at frequencies where each winding current phase … Continue reading nanoVNA-H – measure equivalent core loss resistance

End Fed Half Wave matching transformer – 80-20m – LO1238 variant

A reader of End Fed Half Wave matching transformer – 80-20m asked if a good transformer could be made with with a FT114-43 core. The original transformer above comprised 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 … Continue reading End Fed Half Wave matching transformer – 80-20m – LO1238 variant

End Fed Half Wave matching transformer – 80-20m – 2xFT240-43 variant

A reader of End Fed Half Wave matching transformer – 80-20m asked if a better transformer could be made with a stack of 2 x FT240-43 cores and using half the turns. The original transformer above comprised a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used … Continue reading End Fed Half Wave matching transformer – 80-20m – 2xFT240-43 variant

RF transformer design with ferrite cores – saturation calcs

Ferrite cored inductors and transformers saturate at relatively low magnetising force. #61 material example Lets work through an example of a FT50-61 core with 10t primary at 3.5MHz. Magnetic saturation is one limit on power handling capacity of such a transformer, and likely the most significant one for very low loss cores (#61 material losses … Continue reading RF transformer design with ferrite cores – saturation calcs