I have written online and in many many emails that a very common failure of VNA measurements of components is the test fixture, and the standout problem is most often the length of connecting wires. This article works a couple of theoretical designs based on a validated model and experience of building and measuring many … Continue reading VNA measurement – small is beautiful
Overheating balun cores – an explanation discussed a scenario where an operator reports unstable VSWR after 30s of ATU adjustment. Where the antenna system incorporates ferrite elements, a possible / likely explanation is that loss in a ferrite core has been extreme and raised core temperature to the Curie temperature at which it quickly loses … Continue reading Overheating balun cores – how much power does it take?
Correspondents raise instances of damage to baluns with me from time to time, and there is a steady stream of reports online. One of the very common reports is of something unexpected happening while adjusting an ATU, after perhaps 30s of power applied, VSWR suddenly becomes unstable, changing for some unknown reason, and attempts to … Continue reading Overheating balun cores – an explanation
Correspondents raise instances of damage to baluns from time to time, and there is a steady stream of reports online. The thinking is often “my balun is rated at 5kW, how can I damage it with a transmitter that is only 100W?” This article discusses heat dissipation from a small sealed plastic enclosure. This is … Continue reading Power dissipation of a sealed plastic balun enclosure
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
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)
The transformer is an autotransformer of 3+21 turns single layer close wound on a ‘stack’ of two Fair-rite 5943000601 cores (FT82-43?). Note that these were genuine Fair-rite stock, other #43 mix products in the market place may be significantly different (see Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues for … Continue reading Another small efficient matching transformer for an EFHW – 2 x 5943000601 (FT82-43) – VK4JJ build and measurement
This article documents the process of design, prototyping, measurement and final build of a 1:49 impedance ratio (1:7 turns ratio) EFHW transformer, exploring some alternative designs along the way, a collaboration between VK3PY and VK3TU with a little guidance. The transformer is wound on a Jaycar LO1238 35x21x13mm toroid of L15 material (L15 appears to … Continue reading Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement
(Guanella 1944) described a 1:4 balun, of a type often known as a current balun. From Definition: Current Balun, Voltage Balun: An ideal current balun delivers currents that are equal in magnitude and opposite in phase. A good current balun will approach the ideal condition. It will deliver approximately equal currents with approximately opposite phase, irrespective of the load impedance (including symmetry). Common … Continue reading A simple transformer model of the Guanella 1:4 balun
This article describes a low power digital directional wattmeter based on the design published by G8GYW at https://github.com/G8GYW/g8gyw.github.io . The complete wattmeter was purchased on Aliexpress for around $70, principally for the hardware as it was intended to replace the firmware. Above is the seller’s picture of the wattmeter, it has a different display to … Continue reading Digital directional wattmeter – based on G8GYW – part 1