From: John Woodgate
Subject: Re: low loss transformer availability?
Date: Mon, 6 Jan 2003 19:49:20 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 6 Jan 2003 19:56:26 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Winfield Hill
wrote (in ) about 'low loss transformer
availability?', on Mon, 6 Jan 2003:
>> John wrote...
>>> Winfield Hill wrote
>>>> For example, learning from Jerry Sevick, I designed a wideband
>>>> 16x transformer (RIS-294) that worked in two stages. First 50
>>>> to 12.5 ohms with 25-ohm coax, finishing with 12.5 ohms to 3.2
>>>> ohms using 6-ohm transmission line, made from two wide copper
>>>> strips insulated with a thin layer of Kapton tape. It handled
>>>> over 100W, was flat from 500kHz to well over 50MHz, and could
>>>> deliver over 10A peak into a 3-ohm load.
>>> What I had in mind was how long the cables would have to be to
>>> work at 3 MHz. '500 kHz' makes the answer even more interesting.
>> Not so very long, if one uses a large high-permeability core.
>> 'Course that can hurt on the high end. But I have found that
>> a 100:1 frequency range usually isn't too hard to achieve.
> John, I checked in our records.
Well, thank you for doing that.
> I used an unknown 1.4-inch dia
> toroid made with low-permeability material, and A_L = 155nH/T^2.
> My home-made coax (#14 magnet wire with a Scotch adhesive-backed
> copper tape shield) made 4 turns around the toroid, so L = 2.5uH.
> Being it was a 25-ohm coax, that should have given trouble near
> 1MHz, but in fact we had to go down to 500kHz to load the 50-ohm
> drive to the complete two-stage transformer. Despite the -3dB
> input, the 3-ohm terminated output was only down 20% at 500kHz.
> My data shows an overall flat response from 1MHz up, then +20%
> at 50MHz, and some kind of resonance near 80MHz.
I'm afraid you've lost me. This #14 wire with the foil shield was the 25
ohm line? I don't understand what the core does. Did you have any of the
50 ohm cable wound on the core? How was the 6 ohm 'cable' arranged?
Wound on the core?
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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