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
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.
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
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
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.
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 is Ruthroff’s equivalent circuit, Fig 3 from his paper (Ruthroff 1959). Focusing on the left hand circuit which explains the balun as a transmission line transformer (TLT), and taking the node 1 as the reference, the loaded source voltage appears at the bottom end of the combined 4R load, and transformed by the transmission line formed by the two wires of the winding, and inverted, at the top end of the combined 4R load.
It is the transformation on this transmission line that gives rise to loss of symmetry.
Chris, NX0E, related experience with Dr E M T Jones at TCI where they made, among other things, TCI’s HF baluns. These baluns were compensated using capacitors, and we see that very occasionally in ham grade baluns.
The pigtails can be seen as a short transmission line of higher Zo, and although not uniform, it provides a model for understanding their effect.