This article is an expose of the internals of a common Chinese no-name 1-500MHz Return Loss Bridge available on eBay for around $50 incl post.
Above is the exterior of the device. Specs are sparse: P<23dBm, Directivity>36dB. Continue reading Chinese no-name 1-500MHz Return Loss Bridge
The so-called End Fed Half Wave antenna system has become more popular, particularly in the form of a broadband matching transformer in combination with a wire operated harmonically over perhaps three octaves (eg 7, 14, 21, 28MHz).
The broadband transformer commonly uses a medium µ ferrite toroid core, and a turns ratio of around 8:1. Flux leakage results in less than the ideal n^2 impedance transformation, and a capacitor is often connected in parallel with the 50Ω winding to compensate the transformer response on the higher bands.
David, VK3IL posted EFHW matching unit in which he describes a ferrite cored transformer matching unit that is of a common / popular style.
Above is David’s pic of his implementation. It is a FT140-43 toroid with 3 and 24t windings and note the 150pF capacitor in shunt with the coax connector.
The article End fed matching – analysis of VK3IL’s measurements gives the following graph showing the effects of compensation for various resistive loads. Continue reading End fed half wave matching – voltage rating of compensation capacitors
The net abounds with articles on broadband transformers (ie untuned) for matching End Fed Half Wave (EFHW) antennas to 50Ω. One of the aspects that is common to most designs is that the turns of the primary winding are wound ‘bifilar’ with the start of the secondary winding, indeed the twist pitch is often very short and articles often go into detail on how to make this magic thing.
The magic is that it is supposed to give closer to ideal behaviour of the transformers by way of minimising flux leakage.
The transformer above is styled on the common design, and it consists of a 2t primary and 16t secondary where the primary is wound bifilar, and a third 2t winding wound over the primary end of the transformer between the other turns. Continue reading On winding configuration of EFHW matching transformers
The sign of reactance – a challenge posed a problem, a set of R,|X| data taken with an analyser of a quite simple network and asked readers to solve the sign of X over the range, ie to transform R,|X| to R,X.
The sign of reactance – challenge solution gave a solution to the challenge, and The sign of reactance – challenge discussion provided some discussion about the problem and solution.
Some correspondents have asserted that the challenge (see above Smith chart) contains a response that is contrived for the purpose and not representative of real world antenna systems. Continue reading The sign of reactance – challenge reality check
The sign of reactance – a challenge posed a problem, a set of R,|X| data taken with an analyser of a quite simple network and asked readers to solve the sign of X over the range, ie to transform R,|X| to R,X.
It is widely held that this is a trivial matter, and lots of software / firmware implement algorithms that fail on some scenarios. Though the scenario posed was designed to be a small set that provides a challenging problem, it is not purely theoretical, the characteristics of the data occur commonly in real world problems and the challenge data is derived from measurement of a real network.
Above is a Smith chart plot of the measured data that was transformed to the R,|X| for the challenge. Continue reading The sign of reactance – challenge discussion
The sign of reactance – a challenge posed a problem, a set of R,|X| data taken with an analyser of a quite simple network and asked readers to solve the sign of X over the range, ie to transform R,|X| to R,X.
It is widely held that this is a trivial matter, and lots of software / firmware implement algorithms that fail on some scenarios. Though the scenario posed was designed to be a small set that provides a challenging problem, it is not purely theoretical, the characteristics of the data occur commonly in real world problems and the challenge data is derived from measurement of a real network.
Imported and rendered graphically in ZPlots we have:
The network measured is comprised from analyser, a 2.8m length of RG58/CU, a tee piece feeding a 50 resistor on one branch and on the other branch, another 2.8m length of RG58/CU with a 4.7Ω resistor termination.
The challenge is: what is the sign of X across the frequency range? Continue reading The sign of reactance – challenge solution
Over time, readers of The sign of reactance have suggested that determining the sign of reactance with an antenna analyser that does not directly measure the sign is not all that difficult, even for beginners. The article shoots down some of the most common algorithms as failures on simple cases.
This article gives measurements made from a simple network of two identical lengths of 50Ω coax, a 50Ω resistor and a 4.7Ω resistor. It is a network designed to offer a challenge to the simple algorithms, and it IS solvable analytically… but not with most algorithms and software,
Here is the data from measurement made with an AA-600 and then all – signs removed, so in fact the Xs column is |Xs|.
"Zplots file generated by AntScope" "Freq(MHz)","Rs","Xs" 9.000000,78.13,53.66 9.250000,82.12,51.10 9.500000,86.10,47.83 9.750000,89.46,44.00 10.000000,92.30,39.90 10.250000,94.53,35.39 10.500000,96.21,30.71 10.750000,97.17,26.14 11.000000,97.49,21.54 11.250000,97.30,17.12 11.500000,96.54,13.04 11.750000,95.47,9.14 12.000000,93.92,5.68 12.250000,92.16,2.70 12.500000,90.25,0.17 12.750000,88.13,2.50 13.000000,85.94,4.50 13.250000,83.67,6.15 13.500000,81.45,7.36 13.750000,79.29,8.38 14.000000,77.22,9.21 14.250000,75.21,9.78 14.500000,73.23,10.16 14.750000,71.44,10.37 15.000000,69.70,10.25 15.250000,67.99,10.23 15.500000,66.50,9.99 15.750000,65.10,9.68 16.000000,63.81,9.27 16.250000,62.65,8.72 16.500000,61.59,8.15 16.750000,60.55,7.54 17.000000,59.69,6.86 17.250000,58.97,6.20 17.500000,58.20,5.43 17.750000,57.66,4.68 18.000000,57.14,3.81 18.250000,56.77,2.98 18.500000,56.47,2.16 18.750000,56.22,1.22 19.000000,56.04,0.38 19.250000,56.07,0.50 19.500000,56.02,1.38 19.750000,56.12,2.29 20.000000,56.41,3.15 20.250000,56.68,4.03 20.500000,57.11,4.86 20.750000,57.51,5.72 21.000000,58.06,6.61 21.250000,58.77,7.45 21.500000,59.54,8.22 21.750000,60.47,8.95 22.000000,61.44,9.75 22.250000,62.52,10.34 22.500000,63.77,10.97 22.750000,65.11,11.55 23.000000,66.56,12.02 23.250000,68.11,12.38 23.500000,69.82,12.64 23.750000,71.75,12.82 24.000000,73.67,12.84 24.250000,75.96,12.67 24.500000,78.12,12.27 24.750000,80.40,11.72 25.000000,83.05,10.69 25.250000,85.56,9.68 25.500000,88.29,8.09 25.750000,90.92,6.21 26.000000,93.63,3.91 26.250000,96.17,1.13 26.500000,98.61,2.16 26.750000,100.68,5.92 27.000000,102.51,10.11 27.250000,103.87,14.90 27.500000,104.65,19.98 27.750000,104.71,25.32 28.000000,103.98,30.95 28.250000,102.58,36.48 28.500000,100.14,41.97 28.750000,97.08,47.32 29.000000,93.07,51.86
Imported and rendered graphically in ZPlots we have:
The challenge is what is the sign of X across the frequency range? Continue reading The sign of reactance – a challenge
Ellington describes in a Youtube video his high power matching transformer for an EFHW, he rates it suited to 500W CW.
Like almost all such ‘designs’, they are published without supporting measurements or simulations.
The transformer is intended to be used with a load such that the input impedance Zin is approximately 50+j0Ω, Gin=0.02S.
Analysis of a simple model of the transformer with a load such that input impedance is 50+j0Ω gives insight into likely core losses.
Continue reading Ellington 3 x FT240-52 matching transformer for an EFHW
This is a 2017 update of an article written originally in October 2005, earlier editions published on VK1OD.net which is now offline.
Over recent years to 2002, the number of issued amateur licences was declining, the trend was about 2.8% pa decline over the five years to 2002.
This has concerned some people, who took the view that the decline was a harbinger of the impending demise of Amateur Radio. Continue reading Australian amateur population trends 1998 – 2017
Following on from KL7AJ on the Conjugate Match Theorem, KL7AJ on the Conjugate Match Theorem – analytical solution asked the question Is a ham transmitter conjugate matched to its load?
The answer speaks to the relevance of Walt Maxwell’s Conjugate Mirror proposition to ham stations. Continue reading Is a ham transmitter conjugate matched to its load?