Several articles on this site use the following technique for measurement of transformer performance, and the question arises, how accurate does the load need to be? Let’s set some limits on the range of ReturnLoss of interest. Measured ReturnLoss is limited by the instrument, and in the case of a VNA, its noise floor and … Continue reading EFHW transformer measurement – how accurate does the load need to be?
An online expert talking about compensation capacitors and EFHW ferrite cored transformers opined: If the evaluation is done solely by the effect on measured SWR, whether it is measured with a standard reflectometer or a VNA, then it is just as likely the capacitor is changing the losses in the transformer rather than actually adjusting … Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – capacitor loss
An online expert discussing broadband RF transformers recently opined “… if you measure k, the correlation of k and performance is excellent” whatever “performance” means. Presumably he means k as in the flux coupling coefficient of two flux coupled inductors, ie inductors with mutual inductance (meaning changing current in one inductor induces an EMF in … Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – the magic k factor
This article presents measurements of an EFHW antenna system using the transformer design worked up at 1:49 EFHW transformer using a Jaycar LO1238 core – design workup and bench measurements at 1:49 EFHW transformer using a Jaycar LO1238 core – measurement of losses. The antenna system Let’s take a system view, component views including bench … Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – measurement with antenna
Introduction This article presents a review of a EFHW transformer using a Jaycar LO1238 core, a pack of 2 for $8 at Jaycar stores (Australia). The LO1238 is a 35x21x13mm Toroid of L15 material (µi=1500). Boxed up, it is probably safely capable of about 5W continuous dissipation. The design is described at 1:49 EFHW transformer … Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – measurement of losses
Introduction There are several articles on this site describing EFHW transformers using the Jaycar LO1238 toroid, two particularly relevant ones are: End Fed Half Wave matching transformer – 80-20m – LO1238 variant; and Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement. This article presents a design workup … Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – design workup
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
It is easy to become focused on the behavior of a component, but don’t lose sight of the fact that it is but a component of a system where components interact, and the system response is the bigger / more complete picture. In the article MismatchLoss of severely mismatched EFHW transformer , a caveat stated … Continue reading MismatchLoss of severely mismatched EFHW transformer – system response
In an social media discussion about loss of EFHW transformers under mismatch conditions, one of the gathered experts said: It doesn’t even have to be highly complex Z. Just presenting an impedance other than 2450 sends the loss through the roof. The back to back transformer test is misleading unless the antenna presents something very … Continue reading MismatchLoss of severely mismatched EFHW transformer
Several readers have asked my thoughts on the ARRL EFHW kit. I have not built and measured the thing, but have done the first step in a feasibility study. The transformer design is not novel, it is widely copied and this may be one of the copies. The design is usually published without any meaningful … Continue reading Thoughts on the ARRL EFHW antenna kit transformer