Jeff, K6JCA, kindly sent me a paper, (Dunsmore 1991) which gives design details for a variation of the common resistive Return Loss Bridge design.
This article expands on the discussion at Return Loss Bridge – some important details, exploring Dunsmore’s design.
Above is Figure 3a from (Dunsmore 1991). Continue reading Return Loss Bridge – Dunsmore’s bridge
This article continues on from several articles that discussed the ARRL EFHW kit transformer, apparently made by hfkits.com.
This article presents a redesign of the transformer to address many of the issues that give rise to poor performance, and bench measurement of the prototype. Keep in mind that the end objective is an antenna SYSTEM and this is but a component of the system, a first step in understanding the system, particularly losses.
This is simply an experimental prototype, it is not presented as an optimal design, but rather an indication of what might be achieved if one approaches the problem with an open mind instead of simply copying a popular design. Continue reading ARRL EFHW (hfkits.com) antenna kit transformer – revised design #1 – part 1
Jaycar’s LO1238 ferrite toroid is readily available in Australia at low cost and quite suits some HF RF projects.
The published data is near to useless, so a long time ago I measured some samples and created a table of complex permeability of the L15 material which I have used in many models over that time. It did concern me that measured µi was about 25% higher than spec, which is the limit of stated tolerance. Keep in mind that this is Chinese product with scant data published.
I have measured some samples purchased recently, and µi is closer to the specified 1000, so I intend using this new data in future projects.
Above is complex permeability calculated from s11 measurement of a single turn on the LO1238.
Derivation of the expression for the unknown impedance in an s21 series through measurement arrives at the following expression:
\(Zu=(Zs+Zl)(\frac{1}{s_{21}}-1)\).
The diagram above is from (Agilent 2009) and illustrates the configuration of a series-through impedance measurement. Continue reading Probing the popular s21 series through impedance measurement using NanoVNA-D v1.2.29 cf NanoVNA-D v1.2.40
Fox Flasher MkII and several follow on articles described an animal deterrent based on a Chinese 8051 architecture microcontroller, the STC15F104E.
Fox flasher MkII update 7/2019 documented a rebuild of the enclosure etc.
This is an update after five more years operation outside.
Above is a pic of the device. The polycarbonate case has yellowed a little. Importantly the cheap PVA has not crazed, it is kept dry by the outer enclosure, and a hydrophobic vent helps keeps the interior dry.
The battery is a pouch LiPo single cell, it is in good condition. A previous trial with 18650 LiIon cells showed they were unsuitable for the environmentals.
Two previous articles were desk studies of the the ARRL EFHW kit transformer, apparently made by hfkits.com:
This article documents a build and bench measurement of the component transformer’s performance, but keep in mind that the end objective is an antenna SYSTEM and this is but a component of the system, a first step in understanding the system, particularly losses.
Albert, KK7XO, purchased one of these kits from ARRL about 2021, and not satisfied with its performance, set about making some bench measurement of the transformer component.
Above is Albert’s build of the transformer. Continue reading ARRL EFHW (hfkits.com) antenna kit transformer – measurement
It is often handy to have a reliable / known female UHF short and open circuit terminations when measuring using cables terminated in a UHF male connector.
This article describes a DIY solution.
Above is a diagram from Rosenberger showing the location of the ‘standard’ reference plane on UHF series connectors. Continue reading DIY UHF short and open circuit terminations
Derivation of the expression for the unknown impedance in an s21 series through measurement arrives at the following expression:
\(Zu=(Zs+Zl)(\frac{1}{s_{21}}-1)\).
The diagram above is from (Agilent 2009) and illustrates the configuration of a series-through impedance measurement. Continue reading Probing the popular s21 series through impedance measurement using NanoVNA-D v1.2.29
This article is principally a short commendation for Jupyter or Interactive Python for ham radio related projects for the quantitative ham. Python is a cross platform programming language that has a very rich set of libraries to support scientific and engineering applications, and a good graph maker.
The exercise for this demonstration is to decompose three measurements of currents on a two wire transmission line at a point into the differential and common mode components at that point, and to plot a phasor diagram of a solution to the measurements. Remember that common mode current and differential current in an antenna system are usually standing waves.
Above is a diagram explaining the terms used, I1 and I2 are the magnitudes of currents in each conductor measured using a clamp on RF ammeter, and I12 is the magnitude of the current when both conductors are passed through the clamp on RF ammeter, i12 is the phasor sum of the underlying i1 and i2. Continue reading Jupyter: one for the toolbox – decompose common mode and differential mode current components
The most common problem of broadband ferrite cored transformer designs for RF is insufficient turns which results in:
This article give a simple test for a transformer that will have a nominally 50Ω input or output winding
Without going into a lot of magnetic and transformer theory, a through test using a VNA of the core and just one winding configured as a 1:1 (50Ω:50Ω) autotransformer is revealing. If that combination of turns, core, frequency is not adequate, it is very unlikely any transformer
Above is a schematic of the test configuration, the DUT is the central element, everything else is supplied by the VNA. Continue reading A simple NanoVNA test of a ferrite core and winding to check its suitability in a 50Ω:xΩ transformer