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From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: Binocular choke extras
Date: Wed, 19 Mar 2025 23:24:36 +0100
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On 3/19/25 22:40, Liz Tuddenham wrote:
> I've just taken delivery of a couple of ferrite 'binocular' choke cores;
> each one came with two thinwalled metal tubes and some bits of printed
> circuit board.  The tubes appear to go through the holes in the choke
> and the holes in the boards fit over the ends of the tubes, with copper
> areas that could possibly be soldered to them.
> 
> Does anyone know what purpose these serve?
> 
> 

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.

<https://www.communication-concepts.com/content/AN762/AN762_Application_Note.pdf>

Jeroen Belleman