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, enameled 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

nanoVNA-H – measure equivalent core loss resistance

A very common design of a n:1 transformer for EFHW antennas uses a 2t primary on and FT240-43 (or even smaller) ferrite core. In a process of designing a transformer, we often start with an approximate low frequency equivalent circuit. “Low frequency” is a relative term, it means at frequencies where each winding current phase … Continue reading nanoVNA-H – measure equivalent core loss resistance

End Fed Half Wave matching transformer – 80-20m – LO1238 variant

A reader of End Fed Half Wave matching transformer – 80-20m asked if a good transformer could be made with with a FT114-43 core. The original transformer above comprised a 32t of 0.65mm enameled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load … Continue reading End Fed Half Wave matching transformer – 80-20m – LO1238 variant

End Fed Half Wave matching transformer – 80-20m – 2xFT240-43 variant

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 enameled 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

Comparison of BN43-202 / 5t with BN73-202 / 2t for rx only on low HF – small broadband RF transformer – 50:200Ω

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