There seems to have been a revival in use of the so-called End Fed Half Wave antenna. The prospect that a small radio such as the FT817, a magic match box and 10m of wire makes a good 20m field station appeals to many a SOTA enthusiast. Let us model a scenario with a FT817 … Continue reading Thinking about SOTA, EFHW and EMR safety
A reader of EFHW transformer measurement – how accurate does the load need to be? asked whether the discussion applies more generally, in particular to the loads used for calibration and measurement with a VNA. In this article, unless stated otherwise, reference to |s11| and ReturnLoss are to those quantities expressed in dB. Note that … Continue reading NanoVNA – how accurate does the LOAD need to be – part 1?
A correspondent asked whether I had a tool similar to An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03) to assist in the design of a ferrite cored Ruthroff 1:4 balun for HF. In fact, the problem is the same as the one discussed in the article above, and the … Continue reading A Simsmith model of a Ruthroff 1:4 voltage balun – 2843009902 (BN43-7051)
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
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
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
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
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