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.
Insertion VSWR is the VSWR looking into the balun with a matched load (termination) on its output, it is a measure of imperfection of the balun. It ought to be a specification item for low Insertion VSWR baluns, but it rarely given.
What is not mentioned in the above definition is the symmetry or balance of the load.
In the first article, the measurements at the input of around 7m of 50Ω line were adjusted to move the reference plane to the load end of the coax using the add/subtract cable feature of Antscope to de-embed the transmission line.
The second article used a FA-VA5 analyser and VNWA software to make the measurements and to some extent, de-embed the transmission line. In this case the transmission line was quite short at 370mm, and whilst the facility adjusted for propagation time, it did not adjust for attenuation though that was very small in this case and of little consequence. The FA-VA5 analyser and VNWA software combination would not suit the scenario in the first article as will be demonstrated.
This article examines the response to a 6m length of RG58 with O/C load at 30MHz.