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
Several correspondents refer to my article Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer using medium µ ferrite core for receiving use – 50:200Ω and suggest “I got it wrong, #73 is the proven material choice for such a thing, and a 2t primary is optimal”. … Continue reading Comparison of BN43-202 / 5t with BN73-202 / 2t for rx only on low HF – small broadband RF transformer – 50:200Ω
Guanella’s 1:1 balun and his explanation gave a LTSPICE model of Guanella’s 1:1 balun. The LTSPICE model was of a ‘test bench’ implementation of the balun which comprised an air cored solenoid of two wire transmission line, with a slightly asymmetric lumped load. This article discusses limitations of SPICE in modelling practical baluns. Guanella’s 1:1 … Continue reading Using SPICE on antenna baluns
Guanella’s 1:1 balun and his explanation gave Guanella’s equivalent circuit and analysis of an example air cored choke of the type shown by Guanella. The analysis was presented in an LTSPICE model of a ‘test bench’ implementation of the balun, and it showed that on a slightly asymmetric load, common balance was only good in … Continue reading Guanella’s 1:1 balun and his explanation – Zcm
A balun puzzle asked several questions of this VK5AJL balun which was cited online. Under what circumstances is the current into one terminal of the secondary significantly different to the current out of the other terminal of the secondary? Is this in fact a better current balun than voltage balun under some conditions? What? Is … Continue reading A balun puzzle – discussion
The project is design, implementation and test of a small common mode choke for use with an analyser for antenna measurements. The choke must have medium to high Zcm from 1 to 30MHz. It is intended to be used with analysers supporting SOL calibration, so effectively any impedance transformation within the fixture is compensated and … Continue reading Small common mode choke for analyser antenna measurements using 2843000202 (BN43-202)
One sees lots of articles describing inductors and transformers wound on rectangular cross section ferrite cores, and in explanations, the OD seems to be an important parameter but little consideration is given to ID. Inductance of an inductor on a rectangular toroidal core depends on many factors, and among them ID and OD. Inductance is … Continue reading Choosing a toroidal magnetic core – ID and OD
QST publishes a design by W0SJ for a nominal 50:450Ω EFLW matching device from 160-10m using the following circuit. The article is ‘in-brief’ as technical stuff that will not interest most hams is published privately on a members-only page. This article is based on the information in the QST article alone (ie not on the … Continue reading W0SJ matching transformer for an EFLW (Laird 28B1540-000)
I wrote recently of a flawed test of balance performance of an antenna system and an ATU, and some readers have taken up the issue, basically asking the question “then, how do you measure balance of a two wire line with a scope?” The first step is that you must define what you mean by … Continue reading Measuring common mode current with a scope
This article describes a current probe for use with a power meter calibrated in dBm (eg RFPM1 and RFPM2). For use with RFPM1 and RFPM2, both of which read to 16dBm max, it is convenient that the scaling factor for the probe is 0dBA/dBm, ie that those meters read dBA directly, implying a current range … Continue reading RFPM2 – current probe