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
This article describes a common mode choke intended to reduce RF interference with a VDSL service. The MDF is located where the underground cable enters the building. From here it rises vertically and travels some 25m across the ceiling to the VDSL modem. Last update: 19th March, 2020, 11:08 AM
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 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?
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
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
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
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
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