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
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
I have written many reviews of published EFHW matching transformers, and in most cases the reviews have reported estimated or measured losses that are appalling and not disclosed by the ‘designers’. Why is it so? I am asked, why is it so? Up front, I do not know the answer definitively, but let me offer … Continue reading Common failings of EFHW matching transformers
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
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
Barry, K3EUI, posted some interesting measurements of his MyAntennas EFHW which he described with some useful detail: I have been experimenting with a “MYANTENNA” 130 foot long “end-fed” with the 49:1 UNUN* I replaced their 130 ft antenna wire with a heavier gauge #12 stranded insulated wire (I had a few hundred feet).* This is … Continue reading K3EUI’s MyAntennas EFHW on 80m
Reviewing consistency of measured and model data, the first posting was based on an incorrect model parameter (aol), the article is now revised for the correct value, apologies. End Fed Half Wave matching transformer – 80-20m described a EFHW transformer design with taps for nominal 1:36, 49, and 64 impedance ratios. Keep in mind that … Continue reading End Fed Half Wave matching transformer – 80-20m – model and measurement
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
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