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
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
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
This is a follow up to Thoughts on the ARRL EFHW antenna kit transformer.
The first point to note is that Amidon’s 43 product of recent years is specified identically to National Magnetics Group H material. It is significantly different to Fair-rite’s 43 mix.
Though the parts list specifies an Amidon #43 core, I note that W1VT posted recently: Continue reading Thoughts on the ARRL EFHW antenna kit transformer – improvements?
From time to time, ham radio operators may question whether a section of installed and used coax is still good or significantly below spec and needs replacement.
A very common defect in coax installed outside is ingress of water. The earliest symptoms of water ingress are the result of corrosion of braid and possibly centre conductor, increasing conductor loss and therefore matched line loss (MLL). Any test for this must expose increased MLL to be effective. Continue reading A quick and simple, but effective test of coax matched line loss