Vitrovac tape-wound core T60009-E4006-W650

Let me know if you find something...

Jeroen Belleman

Ha, your cupboard is bare as well..

These

Forget these nanoamor parts, they only have a few sizes in stock and they are about $8 each. I think I have sourced a suitable replacement (at about 50 pence each!) - I'll post an update when I have procured a few and tested them.

I think you'll have trouble getting anything toroidal and amorphous below 9mm OD. There are various possible sources at the larger OD.

VAC had other 6.7mm numbers (9-E5006-W562,9-E4006-W563) that were 4mm H.

Coremaster in TW used to carry 3 parts around 6.7mm OD, between 2.3 and 4mm H, but they dropped unprocessed core sales.

You might be able to dig parts out of old ISDN transformers and filters, if you can find unpotted versions. Ferrites do just as good a job there at

Their unbeaten combination of high permeability and small size made it possible to construct RF transformers with a full decade of bandwidth more than is possible with ferrites. I've used thousands, despite the fact that I never produce large series of anything. I kept finding more and more applications and now I have only a few left over.

Jeroen Belleman

I think you'll find there are ferrite parts that will work in most practical applications.

The wide bandwidth you're talking about usually translates as 'low frequency', where part size reduction isn't just a magnetic issue.

In fact, people working in that area tend to boast about the size and weight of their equipment, as a quality factor.

RL

Well, the high-frequency end of an RF transformer is usually set by its size, the length of its windings. The low-frequency end depends on the overall even mode inductance. It should be evident that if you can get more inductance in a smaller size, the bandwidth gets better.

I have several applications that greatly benefit from wideband RF transformers.

I've made many transformers. Bandwidth with ferrites is always of the order of three decades. With Vitrovac's cores, I got four decades. For Guanella topologies, I even got six decades, maybe a bit more, my best VNA doesn't go beyond 6GHz.

Jeroen Belleman

Above 10MHz, amorphous material may as well not be there. At 6GHz, you're talking Alice in Wonderland, where transformers are concerned - even connectors don't go there.

RL

... anyways, I believe the issue is the difference between

RL

Yes, that is true. In some sense, the secret of wideband transformers is to keep the RF away from the core at high frequencies.

I measured this 6-decade bandwidth, roughly 6kHz to 6 GHz, on a Guanella 25 to 100 Ohm impedance transformer. Those are the easiest as RF transformers go, I admit. I patched together the curves of several instruments and setups to cover the range.

Jeroen Belleman

What amplitude do you expect on the 100R winding at 6KHz?

How many dB down at that same frequency ?

RL

He specified why the bandwidth is remarkable: a Guanella type uses transmission lines of matched delays, in series and parallel combinations -- combinations which differ at either end, hence allowing impedance ratios, and hence also needing a TL with some CMR, hence the core. (Only autoformers can be made, no isolation. Obviously there is _delay_ between all ports, so for example you can have matched delays from an unbalanced primary to complementary (balanced) secondaries, but you can't have perfect balance from one secondary port to the other, because there's delay between them; perfect, instantaneous balance would violate the speed of light.)

The limiting bandwidth is not the winding length, but the winding width: the cross-section of the TLs. And at the ends, how much space is required to connect them up in, and how much mismatch (in terms of impedance and delay) is incurred there.

Tim

At the low end?

That's all the amorphous material is propping up . . .

RL

Well, yes! Nobody claimed otherwise.

Jeroen Belleman

At...the high end.. the end that otherwise depends on length.

Tim

A new flier from MRC in Germany lists a 7.2mm OD part.

NO0704- in 3 different permeabilities.

RL