Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: Binocular choke extras
Date: Fri, 21 Mar 2025 00:08:53 +0100
Organization: A noiseless patient Spider
Lines: 69
Message-ID: <vri765$6npc$2@dont-email.me>
References: <1r9gp9h.1k6o87n8sg91cN%liz@poppyrecords.invalid.invalid>
 <vrfg74$1oqut$1@dont-email.me>
 <1r9hgjn.1ngpfg1zut24qN%liz@poppyrecords.invalid.invalid>
 <n3aotjp01kud0d2mvk8r97hg22nf0fnoc9@4ax.com>
 <jidotjle8u04stdgudgtb7i5am44baat5s@4ax.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Fri, 21 Mar 2025 00:08:54 +0100 (CET)
Injection-Info: dont-email.me; posting-host="66451dd0ffae9f7a8a1f5e8fab4696bb";
	logging-data="220972"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+Xu3zngwxHAX/bZMnCzN4X"
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.13.0
Cancel-Lock: sha1:cXn548S8SjAc0NzDMmQ6QnxkHfc=
In-Reply-To: <jidotjle8u04stdgudgtb7i5am44baat5s@4ax.com>
Content-Language: en-US, fr-FR, nl-NL
Bytes: 4311

On 3/20/25 16:43, john larkin wrote:
> On Thu, 20 Mar 2025 10:49:08 -0400, Joe Gwinn <joegwinn@comcast.net>
> wrote:
> 
>> On Thu, 20 Mar 2025 07:30:58 +0000, liz@poppyrecords.invalid.invalid
>> (Liz Tuddenham) wrote:
>>
>>> Jeroen Belleman <jeroen@nospam.please> wrote:
>>>
>>>> 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.
>>>
>>> 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,
>> 2001, 289 pages, ISBN 1-884932-18-5, TK6565.T7 S48 2001,
>> 621.384'11--dc21.
>>
>> Joe
> 
> I have the Sevick book but it's not very useful.
> 
> We make super wideband tline transformers from micro-coax and pot
> cores.
> 
> https://www.dropbox.com/scl/fi/32s2rfcu4q4iq6l6v1eb4/Pot_Core_TXline.JPG?rlkey=6k7xusurck0jf1ky9n6ja2ebz&raw=1
> 
> https://www.dropbox.com/scl/fi/adcocf1rb7lnanj7zo9xp/TX_1.jpg?rlkey=m7prsxj94fa57ynqoep0ydgnl&raw=1
> 
> Or toroids, which are harder to make.
> 
> https://www.dropbox.com/scl/fi/xuqjzt3h1oq7uexwiu6c8/T750_1.JPG?rlkey=si165mntuu0h40zgsbi0qzxj7&raw=1
> 
> 

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