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
A correspondent asked about the use of a Jaycar LO1238 ferrite core in VK3IL’s EFHW matching unit for 40m and up. The LO1238 implementation would use 3t primary and 24t secondary on the core. If the transformer is simply used without an ATU between it and the radio, and we assume that the antenna system … Continue reading End fed matching – VK3IL design on LO1238
This article describes my build of a Radio-Kits SWR meter (v1.1) and post implementation review. Advertised features: HF coverage – 1.8-30MHz Displays VSWR, forward power, reverse power and supply voltage Peak reading power meter Bar graph or numerical format Reverse power alarm with adjustable threshold Auto turn on in presence of RF – sensitivity about … Continue reading Radio-Kits SWR meter – build and review
(Grebenkemper 1987) describes a directional coupler that has become very popular, especially in commercial implementation. The simplified circuit above from Grebenkemper’s article illustrates the key elements of the directional coupler. An important detail of the design is that the primary of the right hand transformer appears in shunt with the antenna load, and the magnetising … Continue reading Grebenkember’s original Tandem match
A recent online posting gave unequivocal recommendation for the Coil32 Inductance Calculator for application to a ferrite toroidal HF current balun. Always interested in these things, I tried to download it to evaluate it but there was rigmorol to create an account and aware that I have never downloaded a calculator that handled that specific … Continue reading Coil32 inductance calculator
An online poster recently sought to design a broadband 9:1 transformer for HF. Choosing a BN43-2402 balun core, he planned to use a 2t primary and 6t secondary for a nominal 50Ω input. He subsequently posted measurements of the prototype. What might we expect… is it a good starting point. A first approximation at the … Continue reading BN43-2402 balun example
The OCF short vertical dipole for HF has become popular, particularly disguised as a flag pole for low impact installations and encouraged by claims of outstanding performance. The antenna was described in QST and a commercial version was available at time of writing. The rationale for the design is that it is a short dipole, … Continue reading OCF short vertical dipole for HF
I saw a recent discussion where the blind were leading the blind on the dimensions of a twisted two wire line for Z0=50Ω for use in a balun. The poster had used an online calculator which used the well known log function for estimating Z0 of an air spaced two wire line… the calculator, like … Continue reading Z0 of two wire line