Binocular choke extras

This sounds very much like the transformers used in wideband RF power amplifiers. See for example Helge Granberg's application note 762. The tubes with a piece of circuit board form the single- turn low impedance winding, and a number of turns of insulated copper wire going through the tubes form the high-impedance winding. This makes for a good coupling factor and consequently good wideband operation.

Jeroen Belleman

That's the sort of thing I suspected. Each square pad surrounding the end of a tube is individually isolated but they could easily be joined to make a loop circuit with some wire straps.

I intend using this as a 1:1 balun and was worried that the conventional way of twisting the primary and secondary conductors together before threading them through the core would create a capacitive imbalance. If I use the tubes as a 1-turn secondary and thread the inner of the feed co-ax through them, this will give much lower capacitance imbalance.

This also sounds like it could be a transmission-line transformer; these are very wideband. The ferrite cores serve as RF chokes, ensuring the shield and center currents are exactly equal and opposite. It is _not_ an ordinary RF transformer, despite the name.

"Transmission Line Transformers", Fourth Edition, Jerry Sevick, W2FMI,

Joe

Thank you for all your interesting threads as of late, Liz.

It's difficult for me to follow this conversation. Maybe my followup simply repeats what you guys already said. The tubes are shields designed to fit inside the binocular core holes. You then soldier them together with a PCB at each end like so:

It becomes more interesting with coax:

Danke,

I have the Sevick book but it's not very useful.

We make super wideband tline transformers from micro-coax and pot cores.

Can also be used in directional couplers and baluns, which I suppose are just high frequency transformers by another name.

RL

Not at both ends! That is not going to work!

Jeroen Belleman

What you say makes sense in retrospect. Thank you for setting me straight. Although my visual versus verbal thinking tends to favor verbal, for some reason, images work better for me in regards to electronics. For instance, my mind magically sees a Smith chart as a shaped shifted Cartesian reactance plane, where infinities meet in the middle.

An asymmetrical relationship between verbal and visual thinking

Humans rely on at least two modes of thought: verbal (inner speech) and visual (imagery). Are these modes independent, or does engaging in one entail engaging in the other?

Danke,

In retro-retrospect what you say doesn't make sense. Is

What flummoxes me is why shielded coax is is itself inserted into a separately shielded sleeve?

Danke,

Yes, these are transmission-line baluns. The ferrite surrounding the coax acts as a RF choke, ensuring that center and shield currents are equal and opposite, so external fields cancel. The ferrite can be lossy; this actually helps, and suppresses resonances.

I dug deeply into the issue of transmission-line transformers circa

I was implementing such a transformer for use in Fibre Channel and Ethernet compliance measurements, and ended up with insulated semi-rigid coax hand-wound on a ferrite toroid.

Some people to search on include Sevick, Matrick, Ruthroff, and Guanella.

A good source is Motorola AN749 Broadband Transformers.

And the Chinese have been at work. This is open-access:

He, Ding, Zhentao Yu, Jie Chen, Kaiyuan Du, Zhiqiang Zhu, Pu Cheng, and Cheng Tan. 2024. "Modified Broadband Ruthroff-Type Transmission Line Transformer Balun for Isolation-Enhanced Passive Mixer Design" Micromachines 15, no. 3: 332.

Joe

It looks to me that the 3 sections of coax shield are in parallel with the metal tubes and their opposite end shorting bar, forming the low impedance single turn winding, to be connected at the unshorted end with the coax shield connections, hi-Z connections to coax center conductors extending from opposite end - 4:1 balun?

Glen

That one is OK. The tubes connect on one end, but not on the other. There's a gap between the sides in the bottom picture. It will work, though if I were to make it, I wouldn't bother using coax for the high-impedance winding.

Agreed. The coax shields are simply in parallel with the single-turn low-impedance winding formed by the tubes. Maybe it shifts the upper cut-off frequency a tiny bit upwards, but I'm not convinced it's worth the trouble.

Jeroen Belleman

Those are 1:1 baluns. It's not too hard to get stupendous bandwidths with those. Six decades of frequency should be quite easy. It gets harder when you want different impedances at the ends.

Jeroen Belleman

Who is MatricK? Link? Would that be about *matrix* transformers?

Ah, Helge Granberg again. A good one.

When I see 'λ/4' in a transformer description, I lose interest.

Jeroen Belleman

I call them transformers. We use them to isolate pulse generator outputs, and sometimes to get a voltage step-up.

There are windings and a magnetic core, so I'm OK with calling them transformers. A balun is just a specific kind of transformer.

I suppose one end has the shield connected to ground and the other end connects it to something that isn't ground?

Jeroen Belleman

The fast TDR I posted a week or two ago interrogates a balanced line made of two stainless steel rods and inch apart. Using a simple 1:1 ferrite sleeve balun, we measure ~150 ps edges.

Cheers

Phil Hobbs

Danke,

Some people enjoy calling txline transformers "ununs" when neither end is a balanced load against ground.

Is there a balbal?