John, Tony, Ryuji et al,

I’ve done a set of measurements of Inductance of the secondary winding of a WTST on both -61 and -43 mix.
My methodology was to use my RigExpert (good Ukrainian equipment) Zero 30 and in R-L-C configuration. I used known and confirmed values of C from 1740pF(I have some 1% SM) down to 8pF. For each known value of C I would find the resonance point where phase changes from +180 deg to -180deg. Knowing the resonant frequency and the C value allowed me to calculate inductance AT THAT FREQUENCY and plot the values. The first attached .png is an example of resonance.
The first attached plot, albeit very simple, is the 3t output of BN61-202 WTST and you will note that the inductance INCRRASES with frequency, whereas in the second plot of the 2t output of a BN43-202 RWTST, you’ll note the inductance DECREASES with an increase of frequency.
Now I’ve done these plots to specifically complicate the task of those who wish to model the QDC/QMX output transformers WTST and RWTST, of which I’ve included my functional model diagrams for LTSpice, noting that, in both cases, L values for each segment, should be calculated from the either of 3 turn or 2 turn value from the charts.

I hope now that we will see some real life modelling and not just guesses in values and performance.

Vy best 73s

Ross

















Sent from my iPhone 6

Thank you for sharing the report, Ross.

My previous comment got folded on the web view, so please click on Hide quoted text mark to see my response.

This is where you see what I was describing regarding the inductance vs freq. You want to look at the trace for mu'. The mu'' trace indicates the resistive loss component of the core.

Interesting. Do you adjust the number of turns on the core (and use thinner wires) to offset the lower permeability?

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I went to Owen Duffy's ferrite core calculator and obtained the magnetizing conductance. They are indeed much smaller than 0.02 or 0.04 at 5MHz and 30MHz with the range of parameters. So, despite the large differences in the initial permeability and AL values between 61 and 43 cores, the transformer seem to work just as well with the same number of turns.

Hi Tony,

If you use BPF in place of LPF, the component count doubles for the same order number (5 in the case of QMX) and you'll have to insert series caps into existing inductors, and then parallel inductors to the existing shunt caps. I think you would have to annex the filter if you really wanted to do that, and you'll have to make one BPF per band rather than a group of bands. The only advantage I can think of is that the receiver preselector will be entirely absorbed into the TX BPF. That's an interesting concept but I don't see a way to fit many bands into the tiny case.

Re: mystery resonance

I was suspecting (hoping) that the push-pull output transformer's mystery resonance is causing or at least worsening the deep notch I have in my receiver BPF at 25MHz. I changed from WTST to a standard Guanella transformer with separate drain supply RFCs (I had another reason to do that, but the RF behavior of this arrangement is a lot more straight forward than WTST) and did the receiver sweeps. The traces looked unchanged. My BN**-202 core looked dull black not shiny so I assume I got 61 version (I received mine about 2 weeks ago). So, I think the mystery resonance in the output transformer might be something to do with the other winding styles on 43 but I don't think that is an issue with WTST or straight Guanella transformer on 61.

Incidentally, as a primarily high band CW guy, I used 61 core in several of my antenna feedline transformers and they also performed well down to 60m and 80m so I'm familiar with this material. I've always thought that 43 was a bit over-popularized even where other cores would work better. But in reality if the transformer is well designed, the performance difference between 43 and 61 in HF bands may be rather small. Another good ferrite material is Laird 28. This core is somewhat between 43 and 61 (more similar to 43 though).

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JZ, did you look at the drain current and voltage while the transistor is off on that side? That's where the main difference is, in my analysis. I have done all my analysis on paper so I don't have the number to share with you, but if you model the transmission line transformer correctly, it will force RF current to go through the "OFF" transistor and may conduct through the body diodes or cause very high voltage depending on the timing of the switching/driving/etc. Another complication is the coupling of two transmission lines because they share the same core/magnetic circuit. This effect will be more salient at lower frequency especially with 43 core, but may be significant all across. Again, I would expect modeling these transformers accurately to be a quite challenging task.