A symmetric compensation stub using coax

A low Insertion VSWR high Zcm Guanella 1:1 balun for HF – more detail #3 discussed compensation of the Insertion VSWR response of a balun which in that case was wound with coax.

A correspondent wrote of his project with a Guanella 4:1 balun where each pair was wound with a pair of insulated wires, and importantly the output terminals are free to float as the load demands. A Guanella 1:1 balun wound in the same way has the same characteristic.

To preserve balun choking impedance, it is best to preserve balun symmetry, and the use of a short open circuit coaxial stub across the output terminals for InsertionVSWR compensation introduces some asymmetry.

An alternative construction with coaxial cable that is more symmetric is shown above. Continue reading A symmetric compensation stub using coax

Last update: 26th March, 2019, 10:14 AM

Measuring trap resonant frequency with an antenna analyser – measurement of a real trap

Finding the resonant frequency of a resonant circuit such as an antenna trap is usually done by coupling a source and power sensor very loosely to the circuit.

 

Above is Fig 1, a diagram from the Rigexpert AA35Zoom manual showing at the left a link (to be connected the analyser) and the trap (here made with coaxial cable.

Above is the trap measured, the wires were connected as a bootstrap trap as in Fig 1. The coupling link is a 60mm diameter coil of 2mm copper directly mounted on the AA-600 connector, and it is located coaxially with the trap and about 10mm from the end of the trap.

Above is the ReturnLoss plot of the trap very loosely coupled to the AA-600.

Of course this technique will not work on a trap that is substantially enclosed in a shield that prevents magnetic coupling.

Equivalent circuit / simulation

The inductor has previously been carefully measured to be 3.4µH. We can calibrate a model of the coupled coils to the observed resonant frequency and ReturnLoss.

Above, the equivalent circuit. We can calculate the flux coupling factor k from the model, it is 2.3% so this is very loosely coupled to avoid pulling the resonant frequency high.

Above is the simulated ReturnLoss response over the same frequency range as measured.

Conclusions

It is practical to measure the resonant frequency of a trap by loosely inductively coupling an antenna analyser, depending on the structure of the trap and the capability of the analyser.

Practical measurements can be explained with a theoretical model of the measurement setup.

Last update: 21st March, 2019, 6:29 AM

Measuring trap resonant frequency with an antenna analyser

Finding the resonant frequency of a resonant circuit such as an antenna trap is usually done by coupling a source and power sensor very loosely to the circuit.

A modern solution is an antenna analyser or one port VNA, it provides both the source and the response measurement from one coax connector.

Above is a diagram from the Rigexpert AA35Zoom manual showing at the left a link (to be connected the analyser) and the trap (here made with coaxial cable.

The advantage of this method is that no wire attachments are needed on the device under test, and that coupling of the test instrument is usually easily optimised.

Why / how does it work?

So, what is happening here? Lets create an equivalent circuit of a similar 1t coil and a solenoid with resonating capacitor.

The two coupled coils can be represented by an equivalent circuit that is derived from the two inductances and their mutual inductance. The circuit above represents a 1µH coil and a 10µH coil that are coupled such that 3% of the flux of 5% of the flux of one coil cuts the other (they are quite loosely coupled, as in the pic above. Continue reading Measuring trap resonant frequency with an antenna analyser

Last update: 21st March, 2019, 6:30 AM

Comparison of R134a and HyChill Minus 30

I am considering replacing the R134a refrigerant in my car aircon system with a hydrocarbon refrigerant. The candidate is Hychill Minus 30 (HC-30).

This article is a limited comparison of the R134a and HC-30 from the point of view of pressure temperature behavior as it impact practical implementation and measurement.

Exploring HyChill Minus 30 laid down the basis of a CoolProp model of HC-30 for comparison with CoolProp model of R134a.

Fig 1

Above is a comparison of the pressure/temperature of HC-30 and R134a over the range of interest in a vehicle aircon. The typical high and low side HC-30 operating pressure bands are shaded. Continue reading Comparison of R134a and HyChill Minus 30

Last update: 26th March, 2019, 9:48 AM

Exploring HyChill Minus 30

I am considering replacing the R134a refrigerant in my car aircon system with a hydrocarbon refrigerant. The candidate is Hychill Minus 30 (HC-30), a Propane and Isobutane mix.

Fig 1

The p-H (pressure enthalpy) chart of HC-30 above was digitised to derive some comparison charts used for this study. The sampling process necessarily introduces some error, and although small, it causes ripples on graphs of some key values. Continue reading Exploring HyChill Minus 30

Last update: 19th March, 2019, 7:38 AM

Inherently balanced ATUs – part 4

Inherently balanced ATUs reported an experiment to measure the balance of a simulation of Cebik’s “inherently balanced ATU”, and following articles explored balance in some different scenarios, but none of them real antenna scenarios.

As pointed out in the articles, the solutions cannot be simply extended to real antenna scenarios. Nevertheless, it might provoke thinking about the performance of some types of so-called balanced ATUs,  indeed the naive nonsense of an “inherently balanced ATU”.
Continue reading Inherently balanced ATUs – part 4

Last update: 18th March, 2019, 8:21 PM

Broadband providers are not equal

We have had wired broadband service delivered to these premises for almost ten years, supplied by six vendors: Telstra Bigpond, iiNet, Amaysim, Southern Phone, Exetel, Sumo and then Kogan.

During this period, I have conducted routine download tests and recorded the speed. It is interesting to compare performance of the vendors.

This is an end to end file transfer test, and may depend on other organisations for part of the connection. In all cases, the server was provided by an Australian organisation, and probably located in Australia.

Telstra 8Mb/s

Telstra was a monopoly supplier of fixed broadband during this period of service, and it shows in the performance figures. Continue reading Broadband providers are not equal

Last update: 16th March, 2019, 10:03 AM

Inherently balanced ATUs – part 3

Inherently balanced ATUs reported an experiment to measure the balance of a simulation of Cebik’s “inherently balanced ATU”.

This article reports the same asymmetric load using the MFJ-949E internal voltage balun.

The third experiment

The test circuit is an MFJ-949E T match ATU jumpered to use the internal balun and resistors of 50Ω and 100Ω connected from those terminals to provide a slightly asymmetric load.

The voltage between ground and each of the output terminals was measured with a scope, and currents calculated.

Above are the measured output voltage waveforms at 14MHz. Continue reading Inherently balanced ATUs – part 3

Last update: 15th March, 2019, 12:19 PM

Inherently balanced ATUs – part 2

Inherently balanced ATUs reported an experiment to measure the balance of a simulation of Cebik’s “inherently balanced ATU”.

This article reports the same equipment reversed so that the common mode choke is connected to the output of the MFJ-949E.

The second experiment

The test circuit is an MFJ-949E T match ATU followed by A low Insertion VSWR high Zcm Guanella 1:1 balun for HF.  A banana jack adapter is connected to the balun output jack, and resistors of 50Ω and 100Ω connected from those terminals to provide a slightly asymmetric load.

The voltage between ground and each of the output terminals was measured with a scope, and currents calculated.

Above are the measured output voltage waveforms at 14MHz. Continue reading Inherently balanced ATUs – part 2

Last update: 15th March, 2019, 12:19 PM

Inherently balanced ATUs

Hams are taken by fashion and pseudo technical discussion more than objective circuit analysis, experiment, and measurement. Nowhere is this more evident that the current fashion for “True Balanced Tuners”.

LB Cebik in 2005 in his article “10 Frequency (sic) Asked Questions about the All-Band Doublet” wrote

In recent years, interest in antennas that require parallel transmission lines has surged, spurring the development of new inherently balanced tuners.

Open wire lines require current balance to minimise radiation and pick up, the balance objective is current balance at all points on the line.

Cebik goes on to give examples of his “inherently balanced tuners”.

Above, Cebik’s “inherently balanced tuners” all have a common mode choke at the input, and some type of adjustable network to the output terminals. Continue reading Inherently balanced ATUs

Last update: 15th March, 2019, 12:18 PM