Re: Binocular choke extras

On Fri, 21 Mar 2025 00:16:33 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

On 3/20/25 21:49, Joe Gwinn wrote:

On Thu, 20 Mar 2025 08:43:54 -0700, john larkin <jlArbor.com> 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
>

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
2004, and still have most of the stuff from that era, but have
forgotten many of the details.  There were a number of approaches,
each with advantages and disadvantages.  The recipe is in the Fibre
Channel standard, long forgotten.  Fast Ethernet used the line coding
et al pioneered by Fibre Channel.
 
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.

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

No, it's a man's name.  The letter "r" is a typo.

RICHARD E. MATICK

Transmission Line Pulse Transformers-
Theory and Applications

PROCEEDINGS OF THE IEEE, VOL. 56, NO. 1, JANUARY 1968

 
A good source is Motorola AN749 Broadband Transformers.

>
Ah, Helge Granberg again. A good one.

Yes.  AN762 on Linear Amplifiers was mentioned elsewhere in this
thread.

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.<https://doi.org/10.3390/mi15030332>
 
Joe

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

That seems awfully strict for non-native speakers of English.  Such a
rule would pretty much cripple SED.  And the ? mark could well be a
typo.

Joe