Do any free tools allow you to model RF transformers?

[G0HZU]

Like I say earlier in the thread If you just want basic n:1 transformers you can model these in RFSIM99 already because it has a crude transformer model.

However, I can't remember if the transformer model is any good...

But it is a fairly simple task to hand write a 2 port model for a (close to ideal) 4:1 Z transformer and RFSIM99 can cope with 2 port s parameter files.

eg here's about the simplest hand produced model I can think of for a 4:1 unbalanced to unbalanced transformer covering 100kHz to 30MHz. It's not a very sophisticated model but it will probably work very well over 2-30MHz when compared to a well designed TLT for this frequency range if you are just going to put a simple series tank between the two transformers. Port 1 is the low impedance port of the transformer. The transformer is almost ideal over the whole frequency range. In reality, a typical TLT will roll off down around 2MHz and will have some loss at higher frequencies. You can see that I've added a small amount of loss in the model, where the 0.795 should ideally be 0.8. There should also be some departure from ideal phase shift in the model but I've left the angles at 0deg and 180deg. This will probably just affect the tuning accuracy of the peak of the series tuned circuit a little bit up in the higher parts of the band.

# MHZ S MA R 50
0.1 0.6 -180 0.795 0 0.795 0 0.601 0
30  0.6 -180 0.792 0 0.792 0 0.601 0

It's only a starting point but I suspect that this model will be good enough for some early work in RFSIM99 for a 4:1 transformer. You could probably use it even if you cascaded two of the models to get a 16:1 transformer but it would probably be wise to produce a more sophisticated model for this, especially if you want to model a typical TLT down near 2MHz. The model above is too close to ideal down at 2MHz but it is probably going ot be very useful over most of 2-30MHz.

I've put the completed s2p file in a zip attachment below and you should be able to import this into RFSMI99 as a 2 port s parameter file. Try importing two of them and then place a series LC tank in between them and simulate it. It should show a preselector response.

[cdev]

Hi

So really we are really looking for is a cookbook?

That certainly was not on my list of items at all.

As noted in other posts. If you are looking for a cookbook, it's best to spell out what you are after in pretty full detail.

Bob

I edited my last post to make it clear what I would like to do, basically I am just beginning with this, would like to get my ham ticket and get much more serious about QRP, because Ive found I really enjoy making some radio thing work.

Its very relaxing for me. So i hope for a deeper understanding. I don't have any illusions about ever making it a professional anything, however, I enjoy things a lot more when i know a bit about what's happening with something - at least to get over the hump at the beginning, deeper knowledge means more of a flow experience - so its more fun.

[uncle_bob]

I edited my last post to make it clear what I would like to do, basically I am just beginning with this, would like to get my ham ticket and get much more serious about QRP, because Ive found I really enjoy making some radio thing work.

Hi

Ok, well, there are indeed specific designs that have been worked out already to handle most standard matching chores that you run into. There also are pretty good articles showing what these designs are and how they apply. The gotcha is that one set works at microwaves, another set at VHF, yet another at HF. If you are working below HF, the set of things you do changes a couple of times before you get down to audio.  Digging into each of them is fun and exciting stuff. You pretty much need to define a frequency band before you start. To
a lesser extent you also need to decide on power level.

Bob