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
Transmit performance of 2m hand held transceivers reported relative field strength measurements for some transceiver / antenna combinations. This article documents a more careful measurement of the absolute field strength of one combination, and application of that knowledge to the other results. Measurements of field strength were done with Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter … Continue reading Transmit performance of 2m hand held transceivers – absolute gain estimates
This Feb 2012 article has been copied by request from my VK1OD.net web site which is no longer online. The article may contain links to articles on that site and which are no longer available. Many designs have a ‘balanced output’ or an option of a ‘balanced output’, but what does that mean, and are … Continue reading Balanced ATUs and common mode current
This article documents my build of Lou Destefano’s (VK3AQZ) RF Power Meter kit. The power meter is based on probes using an AD8307 logarithmic detector. Above, the RF Power meter with two probes. (The ferrite sleeves were not part of the kit.) Last update: 9th December, 2014, 8:39 AM
My friend Richard found himself located on the margins of coverage of the local 2m repeater where multi path reception was the main problem, a but a little lift in signal would also help. This begs a small Yagi solution. Last update: 23rd October, 2016, 10:20 AM
A reader of Why the preference for Guanella 1:1 current baluns for HF wire antennas asked if a similar model can be built for a Ruthroff 4:1 balun. Hams tend to insist that the Ruthroff 4:1 balun cannot be represented by transmission line elements, but they are quite wrong. Last update: 9th November, 2014, 8:57 … Continue reading A SPICE model for a Ruthroff 4:1 balun.
I am often asked why I recommend a Guanella 1:1 balun with high choking impedance for most HF wire antennas over voltage baluns and 4:1 current baluns. This article explores the topic using SPICE models for a voltage balun, 1:1 current balun, and 4:1 current balun. Last update: 6th February, 2016, 7:15 AM
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
A lot of radios are made today to use an electret microphone which has a higher output than common dynamic capsules and may require a preamp to comfortably obtain sufficient audio. This article describes a microphone + preamp intended as a drop in replacement for an electret capsule. An electret capsule contains an integral FET … Continue reading A simple preamp for dynamic capsules to suit radios using electret microphones
Hams impoverished for space to erect a ‘full size’ antenna for HF pursue a range of options and end fed wires figure highly. New hams who heard the maxim that ‘any antenna is better than no antenna at all’ will try to use bed frames, window frames, balcony railings, anything metallic to get on air. … Continue reading End fed wires – new hams love ’em