I repaced the R134a refrigerant in my car aircon system with a hydrocarbon refrigerant, Hychill Minus 30 (HC-30).
Research had indicated that permeation of reduced barrier hoses was problem with HC refrigerants. The hoses in the car were Goodyear hoses with catalogue numbers, but I was unable to find data on them. Their diameter was comparable to standard barrier hoses, so I proceeded with the trial. Continue reading Post post implementation review R134a replaced with HyChill Minus 30
Recently I have had difficult reaching the local DMR repeater on 70cm, and needed to check that the antenna system had not deteriorated.
I took a baseline measurement with an AA-600 after some refurbishment work in Jan 2018, and was able to compare a current sweep to that baseline.
Above, a wide Return Loss sweep of the Diamond X-50N with feed line compared to the baseline (the thin blue line). Continue reading Diagnosing a possible antenna problem by comparison with a baseline
I am asked about my use of the term
Distortionless Lines from time to time, often in the vein of
they don’t exist, so why discuss them?
The concept derives from the work of Heaviside and others in seeking a solution to distortion in long telegraph lines.
The problem was that digital telegraph pulses were distorted due to different attenuation and propagation time for different components of the square waves.
Heaviside proposed that transmission lines could be modelled as distributed resistance (R), inductance (L), conductance (G) and capacitance (C) elements.
In each incremental length Δx, there is incremental R, L, G and C. Continue reading Do Distortionless Lines exist?
The article On the concept of that P=Pfwd-Prev discussed the question of the validity of the concept of that P=Pfwd-Prev, exploring an example of a common nominally 50Ω coaxial cable at 100kHz. The relatively low frequency was used to accentuate the departure from ideal.
This article digs a little further with analyses at both 100kHz and 10MHz.
A plot was given of the components and sum of terms of the expression for power at a point along the line.
Lets look at the power calculated from voltages and currents for the example at 100kHz where Zo=50.71-j8.35Ω and Zload=5+j50Ω.
Above, the four component terms are plotted along with the sum of the terms. Continue reading Transmission lines: departure from ideal Zo
On the concept of that P=Pfwd-Prev discussed the expression for power at a point on a line in terms of the travelling wave voltage and current components.
The expansion of P=real((Vf+Vr)*conjugate(If+Ir)) gives rise to four terms.
This article looks at the components of that expansion for a mismatched line for a range of scenarios.
- Lossless Line;
- Distortionless Line; and
- practical line.
We will override the imaginary part of Zo and the real part of γ (the complex propagation coefficient) to create those scenarios. The practical line is nominally 50Ω and has a load of 10+j0Ω, and models are at 100kHz.
A Lossless Line is a special case of a Distortionless Line, we will deal with it first.
A Lossless Line has imaginary part of Zo equal to zero and the real part of γ equal to zero.
Above is a plot of the four components of power and their sum at distances along the line (+ve towards the load). Continue reading From lossless transmission line to practical – Zo and γ
A reader of On the concept of that P=Pfwd-Prev asked if / how the scenario discussed could be modelled in SimSmith.
SimSmith uses different transmission line modelling to what was used in that article, but a SimSmith model of RG58A/U allows illustration of the principles and it will deliver similar results.
Let’s explore the voltage maximum and minimum nearest the load to show that VSWR calculated from the magnitude of reflection coefficient is pretty meaningless in this scenario.
Above is the basic model. I have created two line sections, one from the load to the first voltage maximum, and another to the first voltage minimum where I have placed the source. I have set Zo to the actual Zo of the line as calculated by SimSmith (56.952373-j8.8572664Ω), effZ as SimSmith calls it, so the Smith chart relates to the real transmission line. Continue reading SimSmith example of VSWR assessment
Some recent articles discussed some effects that in part are a result of Zo having a complex value (ie a non-zero imaginary part). Continue reading On working with complex Zo
The article On negative VSWR – Return Loss implications raised the question of the validity of the concept of that P=Pfwd-Prev.
The Superposition Theorem is an important tool in linear circuit analysis, and is used to find the combined response of independent sources. Superposition applies to voltages and currents, but not power. Continue reading On the concept of that P=Pfwd-Prev
A correspondent having read my series Measuring balun common mode impedance – #1 related difficulties with his Rigexpert AA-230Zoom.
The articles showed some techniques for measuring common mode impedance of a current balun.
The following examples are of a test choke wound on a BN43-202 binocular core, and the results are quite similar to what might be expected of a broadband HF current balun. The measurements were made with a Rigexpert AA-600.
Above, the measurement result using RigExpert’s newest software Antscope2. Continue reading Measuring balun common mode impedance – #3
The project is design, implementation and test of a small common mode choke for use with an analyser for antenna measurements.
The choke must have medium to high Zcm from 1 to 30MHz. It is intended to be used with analysers supporting SOL calibration, so effectively any impedance transformation within the fixture is compensated and the reference plane is the load side terminals of the device.
The candidate core is a low cost #43 binocular ferrite core that is fairly easy to obtain.
Above is a first pass check of the likely Zcm at 1.8MHz using a Fair-rite 2843000202 (BN43-202) binocular core. These chokes have relatively low self resonance frequency so a value for Cs is supplied that delivers self resonance at around 5MHz. Zcm at 1.8MHz needs 8-9t, 8.5t will be used (ie the twisted pair enters one end of the binocular and leaves the other end for convenient layout). (8.5t is not strictly correct, but it is a close approximation in this case.)
Continue reading Small common mode choke for analyser antenna measurements using 2843000202 (BN43-202)