A Smith chart view of EFHW transformer compensation

I have written several articles on design of high ratio ferrite cored transformers for EFHW antennas. Having selected a candidate core, the main questions need to be answered: how many turns are sufficient for acceptable InsertionVSWR at low frequencies and core loss; and what value of shunt capacitance best compensates the effect of leakage inductance … Continue reading A Smith chart view of EFHW transformer compensation

(How) does this balun work?

I was sent a pic of a balun and asked to explain how it works. With no other detail than the pic, it is difficult to supply a complete answer. Nevertheless, an analysis of what is presented follows. Last update: 6th November, 2020, 5:39 PM

SND implications of variations on the untuned small loop at MF/lowHF

Three recent articles developed an explanation of the YouLoop-2T at MF/lowHF: Small untuned loop for receiving – simple model with transformer ; A transmission line 1:4 impedance transformer ; and Towards understanding the YouLoop-2T at MF/lowHF . The first and third articles explained the concept of signal/noise degradation (SND) statistic, and gave graphs of the … Continue reading SND implications of variations on the untuned small loop at MF/lowHF

WIA 4:1 current balun – further measurements

I mentioned in my article WIA 4:1 current balun that the use of a single toroidal core in the above graphic compromises the balun. This article presents some simple measurements and analysis that question whether the balun works as so many users think. The popularity of the balun derives from the work of VK2DQ and … Continue reading WIA 4:1 current balun – further measurements

4:1 current balun – identifying bad ones

Correspondents have informed me that the balun dealt with in article 4:1 current balun – review and fix and variants are very common. This article gives a checklist of common issues and some basic measurements using an antenna analyser that should reveal some issues without breaking into a sealed assembly. Introduction Baluns are commonly employed … Continue reading 4:1 current balun – identifying bad ones

nanoVNA-H – measuring an inductor – is it a no-brainer?

Let’s explore measurement of a test inductor with the nanovna. Above is the test inductor, enamelled wire on an acrylic tube. An online expert’s advice make this task look like a no-brainer: For a 100 nH inductor you are probably using an air wound coil so you won’t see that much change in inductance with … Continue reading nanoVNA-H – measuring an inductor – is it a no-brainer?

nanoVNA-H – rework of v3.3 PCB to v3.4?

nanoVNA-H v3.4 is out, and I don’t yet see significant problem reports. When I compare the circuit with v3.3 (which I have), apart from new battery charger IC etc, the changes are in three areas: decoupling power to the mixers; increasing the drive to the mixers; and higher attenuation of input on the rx port. … Continue reading nanoVNA-H – rework of v3.3 PCB to v3.4?

nanoVNA-H – measure 144MHz Yagi gain – planning / feasibility

This article documents a feasibility study of using the modified nanoVNA-H to measure the gain of a 4 element 144MHz Yagi, the DUT. The intended configuration is the DUT will be connected to the tx port (Port 1 or CH0 in nanoVNA speak), and a known ‘sense’ antenna connected to its rx port (Port 2 … Continue reading nanoVNA-H – measure 144MHz Yagi gain – planning / feasibility