End fed matching – design review

A correspondent asked me to review an end fed matching unit that uses a FT82-43 ferrite transformer to transform the high impedance of a 40m end fed half wave down to approximately 50+j0Ω. His design uses a primary (radio side) of 3t and secondary of 24t. Last update: 17th September, 2015, 8:43 AM

End fed wires – another matching case study

A reader of my article End fed wires – new hams love ‘em asked about the performance of the matching transformer described at (Osborne 2014). (Osborne 2014) gives the transformer design above using a FT82-43 ferrite toroid with three turns on the primary. The concept is to adjust the antenna length and C1 for a … Continue reading End fed wires – another matching case study

On winding configuration of EFHW matching transformers

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

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

A low Insertion VSWR high Zcm Guanella 1:1 balun for HF

This article describes a Guanella 1:1 current balun which has high common mode impedance (Zcm) and low Insertion VSWR. It is for application on antennas that have low VSWR(50) on at least some bands, especially if they would be used without an ATU on some bands. The purpose of the balun is to minimise common … Continue reading A low Insertion VSWR high Zcm Guanella 1:1 balun for HF

Analysis of a certain dipole animation – OCF implications

A correspondent having read Analysis of a certain dipole animation questioned the validity of the lossy transmission line model of the dipole, citing the case of an OCF half wave which has an approximately resistive feed point. Since the OCF lacks the symmetry exploited in earlier study, we must consider each half of the OCF … Continue reading Analysis of a certain dipole animation – OCF implications